REPLIES TO QUERIES.

In their answers, Correspondents are respectfully requested to mention, in each instance, the title and number of the query asked.

[74034.]-Tempering Tools for Turning Chilled Rolls.-"E. M.'s" reply to "J.J.'s" query is ridiculous. What "J. J." wants is a good caststeel tool, and not cast-iron tools. How on earth is a cast-iron tool going to cut cast-iron in a turning lathe? If "J. J." wishes to temper and harden, heat them slowly to a blood-red, and hold them edgeways on the bosh till quite cold.

ROLL-TURNER.

[74055.]-Electrical Resistance — Probably "Hysteresis," p. 252, would go on his way better if he understood that what is called electric resistance is a pure fiction. The real thing is conductance, and this evidently depends upon the sectional area, be it a wire or a battery cell-that is, size of plates, &c. Double size or area and of course you double the capacity to transmit current. What is called resistance is simply the arithmetical reciprocal of conductance, which enables us to divide instead of multiplying. The true resistance in electricity, as in mechanics, is the friction, which generates heat, and is as C2 in any given conductor.

C

=

electricity at the wrong end, and have not sufficiently mastered fundamental principles. The E R in Ohm's law, C = includes external and inR' ternal resistance. The law states that: "With any given conductor of which two parts are kept at constant potentials, there is a constant ratio between the numerical measure of the potential difference and of the strength of the current which traverses the conductor. This constant ratio depends only on the form, material, and temperature of the conductor, and is usually called its resistance. Different conductors may be compared numerically in respect of resistance, just as in respect of mass, capacity for heat, or any other physical property.' By choosing suitable units of potential difference, current strength, and resistance, we can express Ohm's law thus:-Let E be the potential difference, the current strength, and R the resistance; then E = R or ECR. In the case of a battery cell, E denotes the difference of potential between the terminals when open, and R will be the total resistance made up of the internal resistance of the liquid of the cell and the external resistance of the conductors. If we denote the former of these by r and the latter by R, and E E.M.F., we have C = If any number, n, of elements be joined in series, there is n times the E.M.F.; but at the same time n times the internal resistance and [74055.]-Electrical.-It is impossible for me to the formula becomes n E If the resistance r answer the many questions propounded by n R + r "Hysteresis" in a manner that shall be satisfactory is very small, it may be neglected in comparison to him, unless he either performs the experiment with R, and then we havewhich was suggested, himself, or else is willing to admit that the said experiment, viz., "the gradual immersion of the copper plate into the exciting fluid, the zinc remaining only slightly immersed, that is, a battery of several elements produces no with a corresponding increase of current," is greater effect than a single element. If, however, followed by the results stated by me. Presuming, the external resistance is very great, r is very great that although he cannot overcome his repugnance compared with R, and the latter may be neglected, to perform this experiment, yet he does not deny the truth of the result, I would ask him how it is, the formula being C = that is, the strength, that although I immerse only 1 square inch of zinc within certain limits, is proportional to the number surface, yet I get an increase of current correspond-of cells. If the plates of an element be made m ing to the increased surface of copper immersed? times as large, there is no increase in the E.M.F., When "Hysteresis" has answered this question, I for this depends on the nature of the metal and the will show him how to apply the answer to the liquid; but the resistance is m times as small, for resolution of his own difficulty. As to the measurement of the internal resistance, as described by the section is m times larger, the formula being "Hysteresis," why, no one ever performs it in such a way, so the argument falls to the ground. The same applies to dynamo output. S. BOTTONE.

SIGMA.

[74055.]-Electrical.-May I, as a student of electricity, and as one who has been for some time in the same difficulty as "Hysteresis," presume to get him out of his dilemma? This correspondent, speaking of a reply given by our esteemed friend, Mr. Bottone, says: "What I called in question was his statement to the effect that, by increasing the size of the plates, the internal resistance was reduced in an inverse ratio. I hold that this is not correct, &c." Now, Mr. Editor, your correspondent gives us an

E
R+r

C = =

NE

=

E

C =
n R R'

Hence, an increase in the size of the plate-or, what is the same thing, a decrease in the internal resistance-does not increase the strength to an indefinite extent: for ultimately the resistance of R vanishes in comparison with r, and the strength continually approximates C = "Hysteresis" may find all this in any textbook. He must bear in mind that an ampère is not a unit of quantity, but is the current strength produced in a total resistance of admirable illustra-1 ohm by an E.M.F. of 1 volt. Like every great induction of science, the proof of Ohm's law rests on an infinite series of observations. It has, however, borne the most rigorous tests of absolute accuracy that have been applied to it.

tion that will, I think, when examined, prove the fallacy of his own questions. He says: "I have a chromic-acid cell sufficiently large to contain two sets of plates 4in, square. Each set of plates, when tested separately, give a current of 25 ampères. When the two sets of plates are connected in parallel, they give a current of 50 ampères." He then asks why the resistance is reduced to one half when connected as above. If we take a pail of water and knock a circular hole in the bottom one inch in diameter, there is obviously resistance to the water leaving the bucket to the extent of the bottom of the bucket minus the one-inch hole. Let us knock another one-inch hole, and we shall reduce the resistance to the extent of the diameter of the second hole; and if we had water flowing from that pail or bucket at the rate of one pint per second with one hole, we should certainly with two holes get two pints per second. If we take batteries in place of buckets, the argument holds good. A cell has a tendency to run down, and the more you facilitate this tendency the quicker the cell will do so. The larger the plates of a cell, the more surface there will be for the current to fly to, which is the same thing as making a larger hole in the bucket. The two sets of plates will, therefore, give less resistance because offering more surfacesurface of plate corresponding to size of outlet, and of course, the outlet being larger, more (double in this case) current will flow. This is why the resistance halves itself when the other set of plates is added, and this is why double the current flows. Suppose we had to force through a lin. pipe to the height of 100ft. one ton of water, the best way to

SM.

any rule to answer the question propounded by the querist; but the matter is simple enough. The calculation can be made for both sets of conditions, and then the result of one deducted from the other-the smaller from the larger-will give the loss due to friction. The rules, such as they are, will be found in the textbooks, and if the question is really of much importance, the querist might refer to Hughes's "Treatise on Waterworks," Lockwood and Son. In the case given by the querist, the loss from friction must be small, and, in fact, the question is not worth discussing.

NUN. DOR.

[74125.]-Boiler.-The gauge copper would do; but such questions are really only to be answered by actual trial as to what will be a safe pressure. Fill the boiler with water; apply the fire, and load the safety-valve to what you require. If the valve lifts without the boiler showing leaks, you may safely work at whatever pressure is indicated by the gauge. The water should be at normal temperature, and the boiler should be quite full-the expansion of the water as it is warmed will then "test" the boiler.

T. M.

face condenser. But, without more details, I do
[74126.]-Condenser.-Apparently this is a sur-
not see how anyone can explain, except that the
water from the turbine passing through the pipe
the thing, surely he can see how it acts.
condenses the steam. If the querist has access to
T. M.

[74130.]-Electrical.-It would be necessary to examine these instruments to be able to say how the connections should be made. The information given in query is too indefinite. R.

[74138.]-Valve.-There is surely no great diffi culty in doing what this querist wants; but of what utility is it, and who but himself can be interested in such a device? MECHANICUS. [74140.]-Projection of Light.-In Tyndall's work "On Light," Longmans, or, no doubt, in the back volumes of this paper. What is meant by "detailed record" of experiments on the projection of beams of light through attenuated vapours? R.

a

provides an outlet for the water, his wheels will, [74149.]-Hydraulic Motor.-If "Blayney" the Backus motor illustrated some years ago, and no doubt, work; but he should take a hint from not make such a thing from a disc of pine 3in. thick, R. with buckets 2 in. long.

[74165.]-Eau de Benzoin.-Is this some fancy name for a preparation of perfumery? Benzoin is soluble in alcohol to a considerable extent. Benzoic acid is obtained from a variety of sources; but, as to the eau de benzoin, more particulars must be given. Benzoic acid can be extracted from the gum by Scheele's method with slaked lime and water; but I suspect the querist wants, not "water," but, similar to "lavender water," an spirits, then. alcoholic preparation. Dissolve benzoin in rectified NUN. DOR.

with a coco-nut husk and oxalic acid, swill with [74170.]-Polishing Thin Brass.-Rub over water, and then finish with rouge on a leather.

QUIBUS.

[74173.] Sausage-making Machinery.Any of the firms who make machines for "trade purposes," as they are called, will supply this querist. If in London, he should take a walk round the meat-market, or apply to some of the firms advertising in this paper. T. M. culating horse-power has been given many times. 174177.]-Horse-Power.-The method of calIt is, roughly, 2A.R.S.P.-that is, multiply the area of the piston in inches by the number of revolutions per minute, by the length of stroke in multiply that by 2, and divide by 33,000, and there feet, and by the pressure in pounds, and then is the estimated horse-power. The "indicated" H.P. can be obtained only by the indicator.

66

T. M.

[74081.]-Banjo (U.Q)-As this has apparently escaped "Jo's" attention, perhaps I can give the desired information. The head can be cleaned with indiarubber, or, better still, by loosening the straining screws and sponging with a damp sponge. To put on a new skin, first take the banjo to pieces by disconnecting the shaft from the hoop, unscrewing the straining screws, and taking off the wire ring and straining rim. Then damp the skin, which should be about 3in. larger diameter than the hoop, until soft and pliable. Now lay it flat on the table, right side up, and placing the wire ring on the skin, turn the edge of the skin over the ring and under the straining rim. When you have succeeded-and it is rather troublesome until you get the knack- [74221.]-Woollen - Cloth Wearing.-Your place the whole on the hoop of the banjo, clipping correspondent "L. R." objects to the test of with four of the straining screws. Now get a light tearing to prove the capability to stand hard wear. hold of the rim with the remaining screws, pulling That many common "materials are difficult to up the skin with the slack edge as tight as you can tear is well known, and corduroy, moleskin, and as you work round; but do not on any account sailor's rough navy serge are pretty tough proofs of attempt to tighten the skin by means of the screws this. Your correspondent apparently infers that any more than is absolutely necessary. Now put the fact that they are "common" proves their nonthe head aside to dry, and be careful to keep it wearing qualities. I can only say that after 30 away from the fire. When sufficiently dry, tighten years' experience I have found that when I selected the screws and draw the rim down to its normal a cloth rather for its appearance than its untearposition, cut off the loose edge of the skin, and put able nature, I have made an expensive mistake. the banjo together again. After a few days' use Some very fine and costly cloths tear easily, and the skin will slacken a little, and you can then screw they wear badly as well. If your correspondent it down a bit more. Always use the best American will follow my example, and buy cloth only which skins. The dimensions of the English concert cannot be torn either way by any amount of force, banjos by the best makers are as follows:-12in. he will find it will wear almost as well as leather. diameter hoop, 20in. finger-board; 13in. diameter hoop, 19 in. finger-board; bridge about 24in. from tail-piece. I shall be most happy to give M. H." F. G. WILLATT. any further information in my power, if he re(74055.] Electrical. — I am afraid that quires it. "Hysteresis " and others have begun to learn [74122.]-Turbine.-I do not know that there is

double the flow would be to double the diameter of

our pipe (other things in unison). This would halve the resistance, and the best way to double the flow of a current from a cell is to double the plates or put on another cell in parallel, which, of course, halves the resistance.

BANJOKER.

999.

[74272.1-Cycle Tires.-Get about lb. of tire cement and melt over the fire or spirit-lamp in a tin can. When melted, spread it over the inside of the rim with a tin spoon; afterwards spreading evenly with a hot iron rod or poker. When evenly

[74312.1-Petroleum for Lighting.-It is not worth while pointing out that "Oil-Gas," p. 253, does not quote quite correctly, for he overlooks the force of the word "satisfactory," which is of more importance, as it includes price as well as practicability and convenience. Pintsch's system is well known, and is perfectly successful. I retain my opinion about the systems of "laying-on" gas from petroleum, and I am acquainted with most of those introduced since the time when Mr. Silber read his paper before the Society of Arts. That was, though, a method of supplying the oil itself through pipes. It is illustrated and fully described in the number for January 6, 1871. Other methods can be found in the volumes which have been published since then, so that the querist now knows where he can find all about the subject.

SAML. RAY.

[74330.] Medical Electricity. I am extremely sorry that I have only just seen the query of "Anxious," in the issue of May 1st, or I should not have delayed this answer so long. It seems to me that this case is a very hopeful one for the application of the induced current, and I think that "Anxious" would do best to apply it by means of the wire brush, drawing numerous small sparks from the affected part with the fine wires of the brush attached to the positive pole, holding the brass handle of the negative in the hand, take as strong a current as he can bear, and dabbing the brush over the weak part freely for ten minutes night and morning-this treatment to be stuck to for some months. To attempt the overcoming of the resistance due to the injured nerve (which is in the armpit), it would be useful also to apply on alternate days a galvanic current of about 10 milliampères from the spine, between the shoulders to the bend of the elbow in front; the negative pole on the spine. The battery made by Schall, of 55, Wigmore-street, which he calls his "Patient's battery," is the best I know of for this purpose. GERARD SMITH.

you needn't start to build a cycle. It is practically
all turning work, there being very little fitting.
Centres would be a very bad thing, and would
never give satisfaction, as they would always be
"firing"; the pressure on so small a surface being
too great for lubrication to remain between the
surfaces. Balls are decidedly the best, and cones
come next. If querist wishes more information, let
him write and say what style and weight of machine
he wishes, and I shall be very glad to help him.

J. E. A.

[74380.] Amber and Chloroform. Mr.
Bottone concludes his directions for making this
varnish as follows:-"Do not approach a light
to the room where this is going on, or else an
alarming explosion may take place." This is a
mistake. It is not possible to set fire to chloroform
in the air, nor will it burn from a wick. A lighted
match plunged into chloroform vapour is extin-
guished, and the vapour is not ignited. J. T. M.

like to ask our valued contributor, Mr. Bottone,
[74380.]—Amber and Chloroform.-I should
who replies to this query in the last number of
"Ours," under what circumstances the "alarming
explosion," presumably caused by chloroform
vapour, against which he cautions the querist so
solemnly, would be likely to happen? If he really
thinks that such a danger exists, he had better try
the following experiments, the results of which
will perhaps astonish him. They are common
lecture demonstrations of the properties of chloro-
form, and I have tried them repeatedly:-1.
Saturate a bit of wadding with chloroform and
hold it on a stick in the flame of a candle. It will
not take fire until all the chloroform has evaporated.
2. Pour a little chloroform into a hot beaker, so as
to fill it with vapour, then lower a lighted taper
into it. The vapour will extinguish the flame.
Plunge a lighted match into a little chloroform in a
cup. The match will go out as if thrown into
water. In fact, so far from being dangerously
inflammable, chloroform requires a good deal of
coaxing to make it burn at all under any circum-
stances; and this is one of the great points in favour
of its use as a solvent and for other purposes, as
most other liquids whose properties resemble it in
other respects, such as ether, benzol, &c., are highly
inflammable and, therefore, dangerous.
Bristol.

C. E. FRANK.

3.

Craigholm, Upper Clapton, N.E. [74394.]-Dark Slide.-I omitted to mention in [74349.]-Problem.-Permit me to point out my reply to this query that there are many forms that the reply of "Simonides" on page 254 is of dark slide in use, and that the form chiefly in rather misleading, for it implies that ordinary use in England-viz., those that open up like a treatises on algebra contain methods of solving book for the insertion of the plates are not suitable cubical equations. This is very far from being the for building up in the cheap fashion I proposed. case, and the person who hunted through even The form I thought of at the time is much used on advanced textbooks for the information would lose the Continent, and in it the slide is solid, and the his time. Even such a standard work as Todhunter's plates are inserted by pulling out the shutter almost "Algebra for Colleges and Schools" does not give to the end, slipping in the plate, which is caught at any instructions concerning solving the higher the top by two thin pieces of brass placed over each equations, excepting those equations which may be corner; these are permanently fixed. At the solved like quadratics. The theory of the higher bottom there are also two strips of brass, but they equations is a distinct branch of mathematics, and revolve on a pivot. When the plate is to be put in certainly cannot be found in "any treatise on they are turned aside, the plate is slipped in, the algebra." WM. JOHN GREY, F.C.S., brass slips are turned round to lie over the corner of Analytical Chemist. the plate, and caught in a slit made in the groove [74353.]-Malthouse Cowl.-To develop all lie in. The plate is thus kept in position, so that immediately above the groove made for the plate to the parts of a malthouse cowl properly would re- when the shutter is again drawn for exposure the quire a whole page of the "E. M."; besides I have not time to do it. If you advertise your address in plate does not fall out. Personally, I prefer this next week's issue, I shall be happy to forward slips of cigar-boxes and gluing and pinning them form; and for making on the cheap by building up sketches of patterns for malthouse cowl, or any-together (instead of cutting the grooves out of the thing else you find any difficulty with. E. A. A.

Newcastle-on-Tyne.

[74357.]-Ear-Plugs.-Thanks for replies; but the material I seek is one which, when heated to, say, 130° (or not too hot to be borne), will be plastic enough to take accurately the form of the opening of the ear, and on cooling will set firm enough to retain its shape with some degree of elasticity, and without becoming hard. I have seen toy-heads, or, rather, faces, made apparently of some such material, which I used to think was a preparation of indiarubber, but am told is a compound of glue, sugar, starch, &c. Can anyone tell me the precise ingredients, and how mixed? Cotton-wool alone is too pervious to sound, and does not retain shape so as to be ready for use when required in the small hours" almost without waking. Μυ Νυ.

[74371.]-Door-Alarm.-The most reliable dooralarm to continue ringing the whole time the door is open is one with the platinum spring, as per illustration, which requires no explanation. They

solid), it is very suitable.
Plymouth.

B.Sc.

Donard" a sketch of one of these figures which I have made for a friend. It is supposed to be an athlete practising with Indian clubs. The figure and stand are lft. high, the arms, from shoulder to beginning of clubs, 3in. The clubs are 2in. wide at the broadest part, and 8in. long. The head, body, legs, and stand are cut out of one piece of beech, the face being carved with a penknife, the arms and fists out of another piece, and the clubs are thin, flat pieces of holly. These are not set "full front," but slantwise, like the sails of a windmill. A saw-cut of lin. deep is made in the fists, and the upper part of clubs fixed therein with glued pegs. Between shoulders and body are interposed two small boxwood skate-wheels, turned quite flat on both sides; these are to act as washers, and get the clubs well away from the stand. hole is bored horizontally through the shoulders, a greased piece of stair-rod put through, and the arms wedged and glued firmly on the ends thereof

in the position shown. Another stair-rod (fixed in
a wooden plug in a length of iron gaspipe as s
support) passes up the centre of the figure as a
pivot, a short piece of the same rod being first
driven in and glued to the top of the aperture to
make the balance better. The pivot runs well
above his waistband. In the back of the stand is
this keeps the figure with its face to the wind. The
fixed a thin piece of holly, shaped as in sketch;
two arms should be so balanced that one is the
least shade heavier than the other, so that when at
or quite horizontal. The original of the sketch
rest they will not remain either quite perpendicular
will go through a most energetic performance on
very slight provocation. I used enamel paint to
beautify him.
B. HARCOURT.
[74410.]-Fluorescence.-Try passing the solu
tion through a filter composed of granulated animal

carbon.

F. M. ROGERS.

[74414.]-Wooden Mill-Wheels. Stove the cogs, and soak them for a few hours in linseed oil; beech plank until thoroughly dry; then cut out the cog up the wheel, and then pitch and trim-or, better still, put a cutter through them.

F. M. ROGEES. [74415.]-Soldering Iron.-The best flux is spirits of salts killed with zinc. Tin the cast iron with pure tin and mercury, and the bit with solder, and solder with the latter."

[74396.]-Annuity.-I read your query as meaning that £6 per annum will be paid by the husband during his life, for the purpose of leaving his wife an annuity at his death. If this is so, then, taking money at 3 per cent. (you gave no rate, but 3 per cent. is safe, and if it realises more during the period, all the better, I take it, for bills are generally spoiled in drawing out by being the widow), the annuity should be £46.5908.

Manchester.

W. E.

J. W.

[74418.]-Tempering Mill Bill. The mill

too much heated in the fire. If the steel be burned, stand well when heated to blood red, and plunge they will never stand work. I have found them into rain-water.

[74398.]-Waste-Grease Utilisation.-If not committed to soap-making, and have a local use MILLER. therefor, why not try, say, £100 outlay in setting up small plant for making gas for illuminating or other [74426.]-20c.p. Dynamo.-To MR. BOTTONE. purposes, and perhaps the best is the apparatus by-As you do not refer me to the particular type of E. Mansfield and Sons, 140, Great Clowes-street, machine, and as I have described several hundreds CHANCERY LANE. in these pages, it is impossible for me to give a satis can be purchased from any vendor of electrical apfactory reply. I can only give you general data. 174405.]-Visibility of Light.-CORRECTION. If the machine is of the Siemens H type, it must paratus, price 28., or "Afflor," if he is possessed-The eighth and ninth lines ought to be: "He run at 3,000 revs. per minute; if of the ring or drum of any mechanical ingenuity, could make one himtype, about 2,000. If the armature is Siemens type, self at a very small pecuniary outlay. the wire is wound in the channel; if of the ring H. FENTUM PHILLIPS. type, it is easier to wind if the ring has cogs; if of [74361.]-Safety Bicycle.-Unless you are a the drum type, the two heads must have pegs bit of a mechanic and have a good lathe at hand, inserted to prevent the wire slipping. You will find

would also be able to see a rock rising 12ft. out of
the water at the distance of 5 miles 1,320 yards."
The omission of 12ft. destroys the sense of the

sentence.

[74407.]-Model Sailor.

ECNAL.

I send "Sliev

[74466.1-Watchmaker's Wages in Melbourne in 1889 were £3 to £4 per week. For all information as to wages in Melbourne (Australia), "Colonial Report Annual, No. 4," published by Eyre and Spottiswoode, 1891, price 44d.

see

ROSICRUCIAN. [74467.]-Engine Query.-The cause of that low, grunting sound in "J. J. P.'s" cylinder is the piston-springs being loose. The expansion valve answers the same purpose as the baffler on an engine. When an engine has a link-motion, you never hardly see an expansion-valve attached, but in verticals and horizontals you very often find one. ROLL-TURNER.

[74468.]-Electric Lighting by Battery.1st. Best battery: a set of Fuller cells charged with chromic acid or my depolariser. 2nd. 30 cells of gal. each. 3rd. Cost of 30 cells, if home-made, 58. each, or £7 10s. S. BOTTONE.

[74468.]-Electric Lighting. The best battery is undoubtedly that composed of secondary cells; but they require charging by a dynamo. The next best for your purpose will be a Fuller or two-fluid chromic-acid battery. The number of cells depends upon the capacity of the lamps.

SM.

[74468.]-Electric Lighting. If "Triton" will please refer to reply 74276, in the issue for May 1st, he will find a similar query answered fully. No battery is absolutely free from fumes, but I do not think the slight fume given from the bichromate cell would affect your plants. There is no mistake, however, about it being an expensive method of obtaining the electric light.

F. ASKEW.

[74469.]-Colouring Outside Cement-work. -Morse's patent calcarium, obtainable in a variety of colours of various prices, from 15s. to 388. per cwt.; 150 square yards outside work, two coats to the cwt. Eos.

[74472.1-Cuticle of Leaves.-The best method to obtain cuticles of leaves is by soaking the leaf in soft water (rain-water). Time will vary very much, according to specimen; hard specimens, such as Hoya carnosa, may take a month or longer. When specimen appears to be soaked enough, take one out and try with a needle at the base of leaf; if cuticle comes up readily go on (if not, again immerse). Gently clear it at the extreme edge. Now lay it flat on a three by one slip, and with a pair of forceps gently put it up towards the tip. Hold the lower portion of the leaf on to the glass with a needle or forceps. As soon as you have got cuticle off, place in clean water, brush with a camel-hair pencil; if required stained, and colour is bad, bleach in chlorinated soda solution; stain with aniline or logwood, and mount in the usual way-balsam or glycerine.

UNANSWERED QUERIES.

The numbers and titles of queries which remain unan

swered for five weeks are inserted in this list, and if still
unanswered are repeated four weeks afterwards. We trust
our readers will look over the list, and send what information
they can for the benefit of their fellow contributors.
Since our last, "Banjoker" has replied to 74081.

Path of Neptune, p. 52.

73936. 73942. With 73951. 73980. 73970. 73972.

The Callograph, 52.
Shouldered Pins or Rivets, 53.

Defective Keyseater, 53.
Small Clock, 53.
C.L. Tanks, 53.

74161.
74171.
74172.
74174.

double-fluid bichromate battery, since so much
depends on the distance of plates apart, resistance
of porous cells, temperature, and resistance in outer
circuit. The E.M.F. of the Fuller cell, which is of
this type, is very nearly two volts, and with the
ordinary quart-size, filled with white porous pots,
the resistance is quite 0.25 of an ohm; so that the
current on the short-circuit may be as high as 8
ampères. In practice, such a cell rarely gives more
encircling the porous cells, by diminishing the
than 5 ampères on the short-circuit. Carbons
resistance, certainly increase the current.
zinc plates lft. square, and two carbons lft. square,
a good porous cell, plates not more than lin. apart,
I expect the internal resistance would not exceed
of an ohm; so you might get 20 ampères on the
short-circuit. If you ask "Hysteresis," he may be 74129.
able to tell you the current you should get from 74133.
1sq.ft. of zinc.
S. BOTTONE. 74153.
[74480.]-Size of Battery Plates.-You mis-
take the meaning of the word "ampère." It does not
signify quantity, but current strength, and is the
flow occurring in a circuit when an E.M.F. of 1 volt
traverses a resistance of 1 ohm. If you have a cell
giving 1 volt pressure, and your total resistance is
I ohm, you get 1 ampère, whether your zincs be lft.
or 1 mile square. The only difference is that the
smaller cell ceases to develop electricity sooner than
the larger cell. For instance, consider the case of
two secondary cells. A small cell weighing 401b.
will give 1 ampère for 15 hours through 1 ohm. A
cell weighing 2401b. will give 1 ampère for 700 hours
through 1 ohm. If you make the resistance less,
you get more current. Thus, throughohm it
would only last 350 hours, and if through 10 ohms
it would last 7,000 hours. You want to know,
apparently, the number of coulombs. Well, the
combustion of 1 gramme of zinc in a cell sets free
343 litre of hydrogen; 1 litre of H weighs normally
08957 gramme; and 0000105 gramme
= 1 coulomb. A coulomb is the quantity of elec-
tricity carried by 1 ampère during 1 second. SM.

[74481.]-Secondary Currents. I have not
such practical acquaintance with transformers as
would enable me to answer this question, and as I
am leaving home for a fortnight in a few hours, I
cannot spare time to work out the principles.
current and voltage; but the ratios would depend
Doubling the alternations would materially affect the
on the construction. The arrangement of iron and
wire must be suited to the intended "frequency."
SIGMA.

--

[74481.] Secondary Currents. Let the primary wire be of such a size as to carry the current without any appreciable rise in temperature. Let the section of the secondary wire be of such a size as to carry freely the desired induced current without heating. Let the number of turns in the primary coil bear the same proportion to the turns in the secondary coil, as the voltage of the primary current is to the voltage of the secondary current desired. In practice, transformers are constructed to run at about 100 alternations per second. Any great increase or decrease in the rate of alternation is accompanied by a production of heat. This, of course, has no reference to the ratio of voltage, which remains the same, but it points to waste of current.

[74484.]-Logarithms.-To R. WYNYATES.The logarithm of 1 being zero, that of is less than zero, or is negative. It is in fact 0.30103, as may be seen, if we apply the rule that log. of fraction R. G. MASON, Manufacturing Optician. log. of numerator - log. of denominator. 69, Clapham Park-road, Clapham, S.W. But it is found that there are inconveniences in the use of negative logarithms, and convenience is con[74473.]-Poison for Cats.-The most effective sulted by writing the above logarithm in the shape poison for cats or any other mammals is Prussic acid-1+ (1-0-30103), which is what is meant by applied by means of a syringe inserted in the mouth 1-69897. Similarly, log. is written I-95424; but of the cat. Nothing can be quicker than this. this means 1+ 0.95424, or - 0.04576, the true SM. value. LATRIS. [74474.]-Sprengel Pump.-There is a reason why glass is used-because it is the best material [74484.]-Logarithms.-The method to which "R. W." says he has tumbled is the correct one. for the purpose, and the easiest to work. If you used metal, you could not watch the action of the mercury, and you could not clean the pump with sulphuric acid. You could not get iron tubes with as smooth a bore-as glass.

SM.

[74475]-Naval.-There is no such post as you mention in the Navy. In the merchant service, yes, but I don't know any particulars.

In order to multiply 360 first by the logarithm 1-95424, and then to divide the product by the logarithm 169897, we must reduce these two logarithms to amounts that are both entirely negative. This is easily done by subtracting in each case the mantissa from the characteristic, and we get the entirely negative quantities -04576 and -30103. Now, since these are both negative we may neglect the signs and multiply 360 by 04576 [74477.)-Solvent for Wood.-Your query is and divide the product by 30103 (as "R. W." has too vague. State what you want to do. SM. [74478.)-Colouring White Wine.-You can colour with burnt sugar. I do not think it wise to make public methods of flavouring, as people are only too ready to adulterate.

the

E. R. N.

SM.

[74479.]-Autographic Ink.-If you mean by

Autocopyist" machine, use a saturated solution of alum with colouring matter in it, e.g. indigo. You might do it with transfer ink, and have it lithographed from stone. SM.

[74480)-Size of Battery Plates.-It is almost AN imitation " ground-glass de by flowimpossible to formulate a rule, even approximate, ing the plates or sheets with a milk emulsion-that of the amount of current which can be got from a is, a mixture of milk and gelatine.

QUERIES.

[74485.]-Automatic Musical Instruments.To "A. S. L." AND OTHERS.-Can you tell me if there is any automatic instrument made to work with paper Dualsyreno organ? This has 46 notes, but Mr. Wenham's bands which has a larger compass of notes than the home-made ones have the full compass of five octaves or more. Are there none sold that have as many as an ordinary piano? I should prefer the whole scale on the automatic part, and only 46 notes on the manual part, instead of the reverse, which is now the case.-R. A. R.

BENNETT.

[74486.-Emery Wheels for Gulleting Saws. way of treating emery wheels for gulleting saws! We use -Would any reader of the "E. M." give me the best

steel chisels to hack them round, and find we can't get them true. Is there any better method than that! Also, is there any way of getting rid of the stink!-EGNOL

AMAS.

[74487.]-Oak Water Stain.-Would any of your kind readers let me know how to make oak water stain as vandyke brown. Please state quantities, and how made. sold in shops? They contain ammonia and umber, or ANXIOUS.

above, supplied by a well known medical man. The [74488.]-Medical Voltaic Belt.-I have a belt as plates of copper and zinc are laid together, the one overlapping the other about 3-16in., then a felt pad (also overlapping), then two more plates, then a pad, and so on round back. They are then connected at ends by wires to two plates, copper and zinc, which touch the skin again in the groin, but do not touch each other. I want to know if the skin is sufficient to cause a contact between the plates, as the pads keep them from touching each other anywhere; also if the current would pass from plate in and if there would be much current-the plates are bare one groin through the skin to plate in the other groin; to the skin.-No Sia.

reader kindly give me working drawings of half-plate [74489.]-Bellows Body Camera-Would some bellows body camera, with extending base board, to fold to protect focus screen, the back of camera to move backward for focussing, and the front to be rigid?-PHoro.

[74490.]-Electrical.-Would any of your readers kindly answer the following question given in the Advance stage of the Science and Art Department for this year? "The outside of a gold-leaf electroscope is covered with a network of brass wire. The electroscope is lowered into the inside of an insulated metal vessel How are the leaves affected without touching it. (1) when a charge of positive electricity is given to the vessel? (2) when the brass network is momentarily connected with the earth?" What book should I get to study from for the Honours Examination in Electricity. A. BENJAMIN.

query 73812, page 38, says "he has often melted up old 174491.J-Battery Plates.-"Sm.," replying to battery plates"-I presume, to extract the gold therefrom. There is a process known as "scaling" them-ie, ex tracting the absorbed gold without destroying the plates. If "Sm.," or any other contributor to "E. M," knows how this is effected, will he please instruct?-AMALGA MATOR.

[74492.1-Air and Rain Deposits-Will one of our chemical correspondents kindly answer the following question? If an open tank, with some provision for the exclusion of birds and other animals, were exposed to the air and rain in the open country a few miles distant from any town for, say, a year, and the water it might then contain be entirely evaporated, what, in all probability, would the residue consist of upon being analysed?-B. R.

[74493.]-Bronze.-Can any reader give me a recipe for making a rich, brown bronze for brass-work?-SCOTIA. [74494.]-Dynamo Design.-To Ma. ASKEW OR MB. BOTTONE.-Would you please explain why it is that the resistance of the shunt in dynamos varies so much! According to Silvanus Thompson's "Dynamo-Electrie Machinery," the resistance of the shunt winding for the field-magnets should be at least 324 times as great as that which Mr. Askew gives in answer to question 74294, of the armature; but in the small dynamo the details of May 1, the resistance of the shunt is only 25 times that of the armature, and in many other small machines! drum); but in some instances of larger machines t have noticed the same thing (both in Siemens H and

exceeds 400 times the armature resistance. Is there s eliding scale of resistance from small machines to large ones? or please give rule for finding resistances of shunt in machines of, say, 50 watts to 1,000 watts. Also, will you give details of magnetic resistane s of small machines, say the one described in May 1st E. Mas above: the length, area, and permeability of (1) field-magnets, (2)

armature, and (3) the length and area of the air space? greatly obliged if you would inform me whether it will
Also the ampère turns required for each resistance?-effect the efficiency of dynamo if I wind it No. 18 and
J. H. W.
20 B.W.G.? The sizes should be 040in., and 032, as
[74496.)-Submarine Atlantic Cables.-How given in S. 4. Would it spoil dynamo if used as motor!
-A. M. KAVANAGH.
many submarine cables are laid from this country to
New York and other parts of America, and how many
wires do each contain? Also the names of companies
working above!-RISON.

[74497.)-Railway Signalling.-To MR. STRETTON.-Kindly let me know what system of signalling is used on the leading French and German railways. Are semaphores and interlocking in use? Can you refer me to a book on the subject ?-AIGBURTH.

(74498.)-Small Solenoid.-Many thanks to Mr. Bottone for his ready answer to my query (No. 74392), but he has not quite stated what I want. I should like him to state what ampères and voltage such a coil will take, so that I can know what size of dynamo it would require to work about 100 of such coils in parallel or series. I should also like Mr. Bottone to give the rule used in the winding of solenoids, as I have a lot of books (three of his included), and there is not one that gives a rule for the winding of the above.-BERMUDA.

BURST.

[74511.)-Black Varnish.-Can any reader give me a recipe for a quick-drying black varnish-one that will dry in about five minutes? At present I make use of tinge. I have tried ivory black instead of vegetable, but French polish and vegetable black, but it has a brown it seems to want grinding, which I cannot do. Would the addition of blue make it a deeper black? If so, what blue ? -H. H. F.

I have a small coil that I use for medical work. Could [74512.]-Small Medical Coil.-To MR. BOTTONE. you please give me any particulars as to how to recharge, and the best and strongest, and to last longest, of materials for No. 2 Leclanché cells, as my wife is a great sufferer from rheumatism in legs-in fact, all over. She is really unable to get about, but it is her knees most, and I find nothing does her so much good as electric battery. As a reader, would you be so kind as to tell me, as they cost so much to keep having new ones, and I am a working man. as my wife takes very strong cells, as hers is a bad case? L. O.

[74513.]-Electrical.-How can I get the litharge used in accumulator plates hard, so as it will not break up when being charged? Will a dynamo, 200c.p.. giving 40 volts and 14 ampères, charge twenty accumulators joined in series, the plates being 5in. by 4in., and sixteen in each cell; and how many 20c.p. lamps they would light, and how long, after being fully charged?-YOUNG ELECTRICIAN.

[74514.]-Quick-setting Putty.-Can anything be added to ordinary putty to make it dry hard in, say, a week? I want to use it in places where it will be nearly an inch deep. That usually sold would take at least six months.-F. SEARCH.

[74499]-Paper Pulp.-Is it possible to mould paper pulp into any shape or form, without it being run through the drying cylinders-if so, how?-R. V. RROCKLE[74500.]-Incandescent Platinum Wire.-To MR. BOTTONE.-I am obliged by your reply, and should be very glad to hear where the series of "classical experiments" by Mr. Preece are to be found. My object is to establish an electric cigar-lighter on a circuit carrying 48 volt lamps, the actual voltage being generally about 49 when the battery of 25 cells is discharging, as the leads are rather long. Two kinds of these lighters are to be seen in the shops, one with an internal resistance of some kind, and the other with a lamp, taking about two ampères in series with the lighter. In both cases, the wire, which is threaded through a porcelain disc, is very thin, and by no means presents an adequate incandescent surface for the intended purpose. It would be an advantage to use thioker platinum wire, with two or three lamps of low voltage in series, so as to have about four to six ampères passing. What do you recommend? How many ampères does No. 27 8. W.G. of platinum require?-iron mould. On removing from mould and exposing to

AJAX.

[74501.]-Out-off of Steam in Cylinder.-What is the most popular cut-off of steam now employed, and what number of strokes does the piston of a 3in. cylinder, 6in. stroke, give per minute?-H. P.

[74515.]-Tinning.-Will any of our readers describe
how they tin iron and copper stampings, &c., to get
them bright and smooth! They tell me they use some-
thing besides the ordinary flux-viz., killed spirits and
salammoniac-to make the tin run. Is it so ?-TINNER.

making small tablets of soap in the following manner:
174516.]-Discoloured Soap.-I have lately been
Tallow. 100 parts; 25 bo. c. soda, 50 parts; water, 50
parts (about); brought to the boil, and run into clean
the air for about 24 hours, the surface of the soap, par-
ticularly the edges, turns to a dirty brown colour. Could
any reader inform me of the cause of this, and how I
might remedy it? I may mention that that surface which
is not in direct contact with the air retains its natural
colour. Would it be of any use to inclose the tablets in a
fairly airtight chamber till the soap was dry!-SAPO.

[745 2.-Reducing Emery Stone.-Can any of "Cars" inform me of the best and most economical method of reducing emery stone of large pieces to com- [74517.]-Chances.-The shares of a building society mercial sizes in grain, say from No. 8 to 80 and 90's, and run from 1 to 499. Is an appropriation conducted as also state the best works on the trade?-EMERY. follows quite fair to every member?-Into one bag, (74503.]-Microscopic.-How can I split selenite which may be called the unit bag, are placed ten balls, into films which will give a uniform colour when used numbered from 0 to 9; another, which may be called the with the micro-polariscope? I have tried a thin knife and bag, are placed five balls, numbered from 0 to 4. The tens bag, is similarly filled; into a third, or hundreds water, but the films obtained are variegated in appear-winning number is that formed by three balls, one being drawn from each bag, beginning with the hundreds and ending with the units. For instance, 4, 3, and 2 would mean a win for No. 432, 032 for No. 32, 002 for No. 2, and so on. Doubts have been expressed whether holders of units, tens, and hundreds shares (one, two, and threefigured numbers) are quite equally dealt by. Will your mathematical readers please give their verdict!-STARR

ance. -SALICINE.

[74504.]-Nickel in Steel.-If some of our chemical friends would kindly assist me in determining the percentage of nickel in a sample of steel sent me by a friend, eaid to contain that metal, I should feel obliged. Please say, if possible, the usual percentage. - A YOUNG ANALYST.

BowKETT.

(74505.)-Milk Analysis Certificates.-Can any
of your readers inform me in simple language how the [74518.]-Influenza.-To "THE LYDNEY DISPENSER."
numerically small differences in amount of total solids"-Would you kindly give the proper treatment for the
found by analysis are translated by our public analysts above, together with the symptoms whereby one can dis-
into the large proportions of "added water" given in tinguish the approach of the epidemic? Kindly state the
their certificates.-O. JOHNS.
exact doses and alternations of same (in tinctures)?-Ax
HOMEOPATH.

[74506.]-Piston Rings.-I have a 10H.P. semiportable engine, by John Fowler and Co., Leeds, high pressure. Some time ago one of the rings broke in the piston block, and my engineer has made one wide ring instead of two, and not very well fitted. The cylinder being the least bit out of the round, it loses a deal of steam, and the engineer says it will wear to that. What I wish to know is, would it not be better with two rings in, and whether or not cast-iron rings are best to use in the cylinder, for that is what he has put in. I must tell you that the boiler is a large one, but still has a tendency to prime its water ever since he has put the ring in.-W.

PRIOR.

[74508.]-Condensing.-Will any kind reader give me instructions how to condense the steam from a 3in. cylinder engine! I have no convenience for water-bave it all to carry for my boiler about 100 yards. Will it be possible for me to condense the exhaust so as to pump again into boiler! A rough sketch would oblige.-W. M. [74500.]-Oil-Gas for Engine.-I am unable to get coal-gas on account of distance from town supply, and as I want about H.P. I should like to use gas-engine. I have lathe and tools, so could make the engine, but I am fixed as to the gas. I have heard that a good gas for above purpose can be obtained from ordinary lighting oil, and shall feel obliged for instructions, with rough sketch of generator. Will "Jock" or "Jack of All Trades" please assist? I do not care to use benzoline or gasoline on account of their dangerous nature, even with careful treatment. The oil I get for my lamps is a very lear oil; I put some of that into an old oil feeder and eated the bottom of the can over a candle. I was able to get a nice white light almost immediately at the spout with a match. Is this suitable?-ANGUS BRUCE.

[74519.]-Canvas Hose.-I have some canvas hose
which I am desirous of using as belting; it stretches so
much in dry weather, however, as to be very troublesome,
Can any correspondent kindly tell me of any material with
which I can paint or dress it, so that variations in the
quantity of moisture contained in the atmosphere will
not affect it? -HOSE PIPE.

inform me how to clean an ebony piano. It is almost
[74520.]-Ebony Piano.-Can any reader kindly
to get the marks out as they (on rubbing) only smear,
new; but if it gets finger-marked it is almost impossible
which makes it worse than before.-MICAWBER.

[74521.]-Acrolene.-How can I condense the fumes
(acrolene CH40) evolved in subjecting glycerine to a
high temperature? Is there any other way of preparing
it, and what is it soluble in ?-IGNORAMUS.

[74522.]-Telephones. - To MR. BOTTONE.-Will you kindly tell me how to connect up a telephone which has Stanhope marked on case? It is an instrument with four terminals, with telephone hung on hook in centre, faults are most likely to occur in this instrument, and which acts as a transmitter as well as receiver. What how many batteries of Leclanché type should I require for the signal bells for a distance of about 600 yards!J. B. L.

[74523.]-Tuning the Ocarina.-Will some one kindly inform me how to proceed to tune an ocarina that I have made should I use a tuning-fork and start from the lowest note?-J. W.

(74524.]-Water-Wheels.-Given two water-wheels, one double the diameter of the other, and having the same quantity of water flowing upon each of them at the top per minute, which wheel will do the most work in given time? Friction not considered.-J. M. HUDDERSFIELD.

a

(74525.]-Faulty () Accumulator.-Will Mr. (74510.]-Dynamo.-To MR. BOTTONE.-I am making the following matter? I bought at Messrs Woodhouse Bottone or some other electrical correspondent help me in dynamo to give 60 volts 10 ampères, described in and Rawson's establishment an E.P.S. accumulator, Scientific American Supplement by G. Hopkins, the F.M. to 8 volts, to work for 16 hours. As I only wanted to use it be wound with 121b. No. 18 American W.G., and arma-half an hour a day, I calculated the accumulator would ture with 2 No. 20 A.W.G. Now as I find difficulty in getting these exact sizes in covered wire here, I would be it had been used barely five minutes a day, the charge work for 32 hours; but at the end of a fortnight, although

NOTICES TO CORRESPONDENTS.
J. A. M. (very good), to 1253 by Biene.
CORRECT Solutions to 1252 by D. Mackay, to 1254 by

D. MACKAY.-Thanks for the problem. We hope to start three more tourneys shortly, particulars of which will be duly announced.

received (second versions). The competition for the
W. JAY and LINK.-Games leading up to Problem 1248
prize offered by Mr. Lambert for the shortest game lead-
ing up to this position is now closed. The competitors
are W. Jay (37 moves), Link (47 moves), and G. W.
Middleton (49 moves). The prize is, therefore, awarded
to W. Jay. The moves are as follows:-

Kt-K R 3.
1. P-K R 4, P-K 3. 2. R R 3, B-R 6. 3. P-Q Kt 4.
4. B-Kt 2, P-R 4. 5. B-Q 4, B-B 8.
6. R-Q Kt 3, P-R 5. 7. Kt-Q R 3, R-R 4. 8. K-tB 4,
R-K Kt 4. 9. Kt-B 8, P takes R. 10. P-R 4 P-Kt 4.
11. P-Q R5, P takes Kt. 12. P-R 6, P-B 6. 13. P-R 7,
B-R 3. 14. P-R 8 (R), P-K B 4. 15. P-Kt 3, P-B 5.
16. B-R 3, R-B sq. 17. Kt-K 5. B-B 5. 18. P-K 4, Kt-
R 3. 19. B-R 7, Kt-Q B 4. 20. R-R 4, Kt-Q 6 (ch).
21. P takes Kt, R takes P. 22. K-K 2, P-B 6 (ch).
23. K-K 3, R-B 5. 24. B-K B 5, K-K 2. 25. Q-R sq,
Kt 8, P-R 3
28. R-K B 8, R(B5)-Kt 5. 29. Kt-Q8. Kt B 2. 30. B-
P-Q 4. 26. Kt-B 6 (ch), K-Q3. 27. P-Kt 5, Q takes P.
81. B-K R 7, Q-P takes P. 32. Q-R 2,
85. Q-R sq, P-B 4.
Q-R 6. 33. Q-R sq, P-Kt 4. 34. Q-B 2, K-Q 4.
36. Q-R 2, P-Kt 7. 37. Q-R 8q,
P-Kt 8 (Kt).

H. F. HOSKEN AND BIENE.-You are right: the position in 1253 is impossible.

P. H. WILLIAMS.-Thanks for problem. It shall be examined and reported on.

BIENE.-The author omitted to put a B P at Q 5 in his diagram of 1253. There is still, however, the second solution which you have indicated.

THERE is but one way to get the full value of a machine, and that is to keep it in good repair, clean, well oiled, and taken care of. Nothing ruins machinery like neglect.

THE first patent granted by the United States Government bore date July 31, 1790, and was issued to Samuel Hopkins, for a process of making potash and pearlash. It was signed by George Washington. Only three patents were granted in the first year. They average 75 a day now.

COLONEL KOSLOWSKI has discovered a fresh-water lake to the south of the Sea of Aral in the depresrunning from the marshes, which are overflowed by sion known as Aibu-ghir. It is fed by a stream the Amu Daria, to the north-east. The lake appears to be part of the former great Aralian basin, drying of this region. which has become isolated through the progressive