2.63 grs. (half the quan-) liquor. 1125 3 minutes 5 hours zinc precipitated, but not 5.26 grs. in 250 grs. water 1000 5 minutes 5 hours Only partially precipitated. Influence of Dilution with Water. 1.32 grs. in 250 grs. water 4140 3 minutes 5 hours (Precipitate complete with- Precipitate complete. In comparing the results contained in this Table with those of the previous ones, it will be noticed that zinc is more easily precipitated from its combination with chlorine, and in presence of an excess of hydrochloric acid, than when it is combined with sulphuric acid. Still, in either case, and even in presence of a very large excess of acid, zinc is precipitated, and in many cases completely. Before undertaking a series of experiments to discover a new method of separating quantitatively zinc and copper, the author thought it advisable to examine the various processes which have been proposed of late years, and these are the results: He first made a series of experiments with a process which has been recommended by Messrs. Rivot and Bouquet, and which consists in adding an excess of ammonia to an acid liquor containing the above two metals, and then adding caustic potash in slight excess. The liquor is to be heated to 158° Fahr. until the whole of the ammonia is expelled, the copper being thrown down in the state of black oxide, whilst the oxide of zinc remains in solution; but Mr. Calvert has always found, even in employing diluted liquors and a very slight excess of potash, that a certain proportion of hydrate of oxide of zinc, dissolved in the caustic potash, was dehydrated, became insoluble, and precipitated with the oxide of copper, thereby increasing its relative proportion, and rendering the results incorrect. The two methods having failed in his hands, although he had taken all the necessary precautions recommended to carry out those processes successively, he next had recourse to the methods proposed by M. Flajolot. The first consists in adding to a boiling solution of zinc and copper, rendered slightly acid by sulphuric acid, hyposulphite of soda, until no more black protosulphuret of copper precipitates, filtering, and determining the copper by oxidizing the sulphuret with nitric acid in the usual way, and throwing down the copper. The zinc is precipitated with carbonate of soda. The second process given by this chemist consists in estimating the copper by precipitating it in the state of protoiodide by a solution of iodine in sulphurous acid. Both these processes of M. Flajolot gave very satisfactory results, and can be adopted when a complete analysis of an alloy of zinc and copper is required; but as these methods require too much time when rapid analyses are desired, the author next tried M. Pelouze's method, which consists in rendering the liquor containing salts of zinc and copper alkaline with an excess of ammonia, and pouring very gradually into it a standard solution of monosulphuret of sodium, which first precipitates all the copper as black sulphuret, leaving the zinc in solution. As this latter metal yields a white sulphuret, it is easy to ascertain when all the copper is precipitated. This method is * For further details see 'Chemist,' vol. i. p. 411. so easily and rapidly performed, that he thought it advisable to test its accuracy, and the following results leave no doubt as to its exactitude and value. The zinc is determined by difference. Taken. Obtained. Description of Dr. CLARK'S Patent Process for softening Water, now in use at the Works of the Plumstead, Woolwich, and Charlton Consumers' Pure Water Company, together with some Account of their Works. By D. CAMPBELL, F.C.S. According to the author, the process of Dr. Clark for softening water may be applied with advantage to water from the chalk strata, water from the New Red Sandstone, and waters which contain carbonate of lime in solution from any strata. It is briefly described as follows; namely, by adding a quantity of milk of lime to the water, it takes carbonic acid holding carbonate of lime in solution; and forms a precipitate of carbonate of lime, throwing down at the same time the quantity of carbonate of lime held in solution by the carbonic acid, and thus rendering the water soft. The works and operations for carrying out the process were fully described by diagrams. One peculiar feature in the water after it had been softened, and which was not anticipated by Dr. Clark when he first took out his patent, is, that it does not show the slightest sign of vegetation, though exposed to the sun and light for upwards of a month, whilst the water before softening cannot be kept above a few days without producing Confervæ; and if this be not immediately removed, decay commences quickly, and small insects are soon observed, which feed upon the decaying vegetable matter; and the water soon assumes a bad taste. This is continually the case when the water is kept in large reservoirs, and its removal occasions considerable trouble and expense. The author had endeavoured to explain the reason of this marked difference between the unsoftened and the softened water; and he was nearly satisfied that the vegetating principle in the water was more especially due to the carbonic acid holding the carbonate of lime in solution than to the volatile matter, or, as it is sometimes called, organic matter. The process is applicable to many towns already supplied with water from the chalk and from the New Red Sandstone, and if properly applied will be found to pay the expense of its working, and confer a great boon upon the populations, the enlightenment of whose corporations may induce them to adopt it. On the Preservation of the Potato Crops. By Chevalier DE CLAUSSEN. At the meeting of the British Association in Hull, two years ago, the author proposed sulphate of lime as a means of preserving the potato. He has since, by successive experiments, convinced himself that it is entirely efficient. He wets them with water acidulated with sulphuric acid (1 part acid, 500 parts water), and before they are dry throws over them powdered sulphate of lime, or plaster of Paris, by which process they are covered with a thin film of sulphate of lime. If the potatoes are already attacked partially with the disease, they must be left from six to twelve hours in the acidulated water before the sulphate of lime is used; but in case they are free of disease, a few minutes are sufficient. It is very possible that sulphate of lime, with an excess of sulphuric acid added to the soil in which potatoes grow, may be useful; but he has not made any experiment to this purpose. He has ground to suppose that chemical combinations in contact with animal or vegetable products have a tendency to preserve them, in the same way as the combination of oxygen and zinc preserves iron, and that this is one of the causes why the combination of water with the sulphate of lime preserves potatoes and other vegetables; and that in the same time the small quantity of free sulphuric acid destroys the fungus which causes the disease. On the apparent Mechanical Action accompanying Electrical Transfer. By Mrs. CROSSE. Dr. Playfair stated, that at the last meeting of the Association, Mr. Crosse, who is recently dead, had read a communication on some phænomena which took place in the electric current, and it was objected on that occasion, that it was possible the gold which was carried over might have been impure gold; and that it was owing to a solution of copper that was in the gold that these mechanical phænomena ensued. Mrs. Crosse, with a desire to show the accuracy of her husband's experiments, had since his death repeated the experiment with pure gold, and obtained the results mentioned in the communication. Extracts from a Letter from the Rev. A. S. FARRAR, of Queen's College, Oxford, on the late Eruption of Vesuvius (read by Dr. DAUBENY). The writer sketched the recent history of the volcano down to the late eruption. A new crater was formed in December 1854 by the sudden giving way of a portion of the summit of the great cone, which, however, revealed little of the internal structure of the mountain, though it discharged only gas. The eruption commenced on May 1st, 1855, from ten craters which broke out in one long line down the north side of the cone. The lava continued to flow for twenty-eight days, and destroyed much valuable property, passing down the ravines between the Monte Somma and the Observatory, and pursuing its course in the plain to a distance of six miles. Professor Palmieri has taken meteorological observations at the Observatory near the Hermitage. The magnets were affected for two days previously to the outburst of the lava, with remarkable oscillations analogous to those observed in 1851, during the earthquake at Melfi. The development of electricity was strongly marked, of a nature always positive, and yielding different results when studied with a fixed conductor, and the same made moveable according to Peltier's method. The Neapolitan Professors Scacchi and Palmieri intend to publish their observations. Mr. Farrar concluded with an account of M. Deville's Chemical Observations on the gases emitted by the fumaroles, as recorded in the 'Comptes Rendus' for June and July, 1855. On an Indirect Method of ascertaining the presence of Phosphoric Acid in Rocks, where the quantity of that ingredient was too minute to be determinable by direct analysis. By Professor DAUBENY, M.D., F.R.S. The method employed was to sow on a portion of the rock, well-pulverized, and brought into a condition, mechanically speaking, suitable to the growth of a plant, a certain number of seeds in which the amount of phosphoric acid had been determined by a previous analysis. It is evident, that whatever excess of phosphoric acid over that existent in the seed was detected in the crop resulting, must be referred to the soil in which the plant had grown, and hence would serve to indicate the existence of that quantity at least in the rock. Now when chalk, oolite, magnesian limestone, red sandstone, and other rocks in which organic remains are usually present, were made the subject of experiment, the existence of phosphoric acid in the rock was always detected by the foregoing method, the phosphoric acid in the crop exceeding the amount of that in the seeds sown. But when the slates that lie at the bottom of the Silurian system, such as those of Bangor and Llanberris in North Wales, were tested in the same manner, the almost entire absence of phosphoric acid in them was inferred from the scantiness of the crop, which in each instance contained scarcely more of phosphoric acid than had been present in the seeds from which it had been derived. Nor was this owing to any mechanical impediment to their growth; for when the rock was manured with phosphate of lime, a crop was obtained from it as large as in the preceding cases. These experiments tend therefore to show that the rocks above named really were deposited where no living beings existed; for although the absence of organic remains in them might be accounted for by metamorphic action, the heat which obliterated the latter would exert no influence upon the phosphoric acid which all animals and vegetables contain, and which therefore would still remain in a rock made up in part of their exuviæ, even if it had undergone fusion. Dr. Daubeny suggested that this method of investigation might throw some light upon the much-disputed question, whether any rocks are known which were autecedent to the commencement of organic life; and also, in a practical point of view, might be useful by showing, whether manuring with phosphate of lime was likely to be serviceable in increasing their agricultural value. The second subject adverted to in this communication related to the reputed existence of phosphoric acid in certain rocks of Connemara in Ireland, which Sir Roderick Murchison had referred to the Silurian epoch. These limestones, although totally destitute of organic remains, and possessing all the characters of primitive limestone, being crystalline and interstratified with quartz rock and mica slate, often contain, according to a recent analysis, a large per-centage of phosphoric acid; and this statement, Dr. Daubeny, from a hasty examination which he had made of them upon the spot, was disposed to credit, so far at least as relates to the presence of traces of this ingredient in the limestones referred to*. Should this fact be substantiated by further investigations, it will not only confirm Sir R. Murchison's previous opinion as to the age of these limestones, but will also show that they are likely to be of value as manures, by reason of the phosphoric acid which they contain. On the Action of Light on the Germination of Seeds. By Professor DAUBENY, M.D., F.R.S. An opinion has gone abroad, and has found a place in several standard treatises †, that as the luminous rays favour the development of the growing plant, so the chemical rays promote the germination of the seed. The authority upon which this statement rests, seems to be that of some experiments instituted by Professor Robert Hunt, who, whilst employed in investigating the chemical action of light upon inorganic bodies, and its application to photography, turned his attention likewise to the influence of the same agent upon plants. One circumstance alone, however, might raise a doubt as to any direct effect having, in the instances reported, been produced by the several solar rays, namely that, so far as can be collected from the statement given, all the seeds tried by Mr. Hunt were buried in the ground to the usual depth. Now I found that a depth of two inches of common garden soil was quite sufficient to intercept the rays of light, so as to prevent the slightest chemical action being exerted upon highly sensitive paper placed beneath it. The improbability, therefore, of a ray of light acting through such a medium induced me to institute a set of experiments, in which the seeds were placed on the surface of moist earth exposed to the action of particular portions only of the solar spectrum. Although the results obtained are rather of a negative than of a positive description, and have likewise been in some measure superseded by the researches already published by Dr. Gladstone, yet as the experiments have been repeated during the last summer, and lead uniformly to similar results, they are communicated, as justifying the conclusion to which I had arrived, that no positive influence of a direct kind in promoting germination can be traced to the chemical rays of light, when compared with other portions of the sunbeam. Six sorts of seeds were in general employed in these experiments, and the number of radicles and plumules of the several kinds which had protruded each day were duly registered. The media employed for isolating certain rays, or at least particular portions *These limestones have been since examined more carefully by Dr. Daubeny, and the quantity of phosphoric acid present in them found to be much smaller than that reported in the analysis referred to. See Proceedings of the Ashmolean Society for Oct. 29, 1855. + See in particular Mrs. Somerville's work on Physical Geography. of the spectrum, are enumerated in the table annexed, by reference to which it will be at once seen, what specific luminous influence was exerted upon the seeds by each of those coloured glasses or fluids which are named in the brief statement of the experiments which follow. I am indebted to Mr. Maskelyne, the Deputy-Reader of Mineralogy at Oxford, for having examined the various media employed, and defined by reference to Frauenhofer's lines the exact quality of the rays transmitted by each, as is stated in the Table. (See Plate VI In the first set of experiments a south aspect was selected, and the following seeds were experimented upon, viz. But as none of the two first came up, the real number operated upon may be estimated at 69. Of these 46 radicles and 18 plumules came up under violet light. 44 radicles and 18 plumules came up under green glass. 41 radicles and 19 plumules came up in one instance 41 radicles and 5 plumules came up in another instance} in darkness. 36 radicles and 26 plumules came up under cobalt-blue glass. 32 radicles and 17 plumules came up under amber glass. 29 radicles and 7 plumules came up under ruby glass. 23 radicles and 5 plumules came up under orange glass. Accordingly, in this series a slight superiority seemed certainly to belong to the violetcoloured medium over the rest, in relation to the number both of radicles and of plumules which appeared; whilst in respect to the quickness of their germination, the violet and green media were a-head of the rest, although the plumules did not follow the same order. When, however, the same experiments were repeated in a north aspect, the same law did not hold good, for out of 69 seeds, 52 radicles and 22 plumules appeared under green glass. 49 radicles and 17 plumules appeared under blue glass. 47 radicles and 14 plumules 47 radicles and 21 plumules appeared in darkness. 44 radicles and 17 plumules appeared under transparent glass. 39 radicles and 23 plumules appeared under violet light. And with respect to the quickness of germination, it appeared that the green stood first in order; that the seeds under blue and violet glass and in absolute darkness came up next in order, and with nearly equal rapidity; that those in full light were next in order; whilst orange, ruby, and yellow were about equal, but somewhat later than the rest. It did not appear, therefore, from this last series of experiments, that violet light favoured germination at all more than any other species of light; nor indeed that any kind of ray was injurious to the process, so long as its intensity was not too great, as may be inferred to have been the case in the first set of experiments, where the seeds were exposed to the full rays of the sun in a southern aspect. I therefore, in my subsequent experiments, selected uniformly a north aspect for the germination of the seeds; and in order still further to test the point as to whether the quality of the light had anything to do with the process, I placed as before upon the surface of the soil, in boxes, ten seeds of each of the four following plants, viz. peas, beans, kidney-beans, and a species of sunflower (Helianthus annuus), all of which germinated. Now in this case 37 radicles and 25 plumules appeared in the dark box; 34 radicles and 24 plumules appeared under transparent glass; the whole number of seeds operated upon being only 40, |