temperatures at which these elements would not of themselves combine. And it has been ascertained by myself, that common oxygen in contact with these metals, when they are in a finelydivided condition, turns tincture of guaiacum to a deep blue. Mercury also exhibits the same comportment; and since, from its fluid condition, contact between it, oxygen, and oxidizable substances is very readily and completely effected, we can produce many oxidizing actions better under the influence of this metal than even with gold, silver, &c. Freshly-prepared tincture of guaiacum shaken with chemically pure mercury and common oxygen is instantaneously coloured dark blue. Water rendered bluish by indigo solution is decolorized by similar treatment. Aqueous hydrochloric, hydrobromic, hydriodic, hydrosulphuric, and hydrocyanic acids, give up their hydrogen with greater or less rapidity to free oxygen when in contact with mercury, with the formation of chloride, bromide, iodide, sulphide, and cyanide of mercury. By shaking a solution of iodide of potassium with mercury and oxygen gas, iodide of mercury and potassium is produced along with free potash, &c. These and other oxidizing actions effected by means of mercury, show in the most evident manner the chemically exciting influence which this metal exerts upon common oxygen,-in other words, that mercury puts this gas in a condition in which it acts chemically, like the oxygen changed by electricity or phosphorus. From which fact we may certainly be allowed to draw the conclusion, that the catalytic actions of mercury which we have mentioned depend, just as do those of platinum, gold, phosphorus, &c., upon an allotropizing influence which this substance exerts upon common oxygen. . With respect to their capacity of producing a great change in the chemical condition of common oxygen, there is a tolerably numerous class of substances which are of the greatest importance in a theoretical point of view, and to which we must on that account devote our especial attention. These are such substances as associate themselves very readily with common oxygen, but in so doing change it in such a manner that it may be transferred with ease from this combination to other oxidizable substances; that is, it exhibits a relation quite similar to that which marks oxygen modified by electricity or phosphorus. By far the most remarkable substance of this kind is deutoxide of nitrogen (NO2), which even in the cold and in the dark unites with two equivalents of common oxygen to form the so-called hyponitric acid. Of this acid we know that it very readily gives up half its proportion of oxygen to a great number of oxidi zable substances, that is, it comports itself as an eminently oxidizing agent. It readily decomposes indigo-blue dissolved in sulphuric acid, turns tincture of guaiacum to the deepest blue, separates iodine from iodide of potassium, changes aqueous sulphurous acid immediately into sulphuric acid, a solution of yellow prussiate of potash into red, &c., and NO2 is eliminated in these reactions. From these facts it is clear that the two equivalents of oxygen which are taken up by the deutoxide of nitrogen act in many cases just like oxygen allotropized by electricity or phosphorus, on which account we may also assume that hyponitric acid is nothing else than ozonized deutoxide of nitrogen, or NO2+28. But if this assumption is admissible, it follows, further, that deutoxide of nitrogen possesses in a very high degree the property of ozonizing oxygen. And since NO2 not only transforms O into Ŏ, but also unites with this Ŏ as such, deutoxide of nitrogen may be looked upon as the most decided exciter of oxygen (Sauerstofferreger) and carrier of Ŏ (Ŏ-träger); and hence it is that it plays such an important part in certain oxidizing processes; for example, the conversion of SO2 into SO3 by means of atmospheric oxygen. The first degrees of oxidation of manganese and iron are distinguished by the readiness with which they are oxidized by common oxygen to peroxide of manganese and peroxide of iron. And of the oxygen united with the protoxide of manganese or of iron, it is well known that it comports itself in many cases like the Ŏ associated with NO2. Peroxide of manganese even alone turns tincture of guaiacum blue, and peroxide of iron does so when it is dissolved in an acid; peroxide of manganese decomposes solution of indigo just as dissolved peroxide of iron does; peroxide of manganese oxidizes sulphurous acid; peroxide of iron and its salts do the same. In short, both these oxides comport themselves as oxidizing agents like hyponitric acid, for which reason we may compare MnO and FeO to NO2, and consider them, like this, as exciters of oxygen and carriers of Ŏ. If protoxide of manganese or protoxide of iron were liquid or gaseous instead of being solid, they would probably ozonize common oxygen as rapidly and energetically as NO2. Different from NO2, FeO, MnO in degree, indeed, but not in kind, is the comportment of certain other metallic oxides; and in this respect we must notice oxide of barium, which, although perfectly indifferent to common oxygen in the cold, unites with it to form peroxide of barium at a moderately high temperature. That the oxygen taken up by the BaO is in the Ŏ condition, needs, I think, no further proof; and it is clear that BaO, like NO, &c., can ozonize or allotropize common oxygen. It is known that KO, NaO comport themselves quite similarly to BaO. Oxide of lead also, in the cold, is quite indifferent towards com mon oxygen; but at a higher temperature it changes, partially at least, into peroxide, which unites with the remainder of the oxide to form red lead, and the oxidizing actions of the peroxide of lead show clearly enough that one equivalent of oxygen in this compound is in the ozonized condition. We may therefore ascribe to oxide of lead also the property of transforming, under appropriate circumstances, O into Ŏ, and of being the carrier of this Ŏ. I have already shown, years ago, that the oxygen ozonized by electricity or phosphorus combines with PbO to form peroxide even in the cold. [To be continued.] XXXIX. On Electric Pauses. By Professor RIESS*. A SINGULAR effect connected with the discharge from the conductor of a machine was observed by Gross, and described under the name of "Electric Pauses," in the year 1776. The same effect was accidentally observed by Nairne during his investigations on the best form of lightning conductors, and described in Hutton's 'Abridgement of the Philosophical Transactions' for 1778. The phænomenon consists in the disappearance and reappearance of the electric spark when the discharging distance is gradually augmented. Prof. Riess has recently repeated these experiments, and describes the following arrangement made use of by himself as an easy and sure means of obtaining the effect referred to. To the conductor of an electric machine a brass arm was screwed, and united by a ball-and-socket joint with a brass bar 8 inches long and 2 lines in thickness, which carried at its end à brass ball 1 inch in diameter. The arrangement is shown in fig. 1. At the edge of a table a glass rod was fixed which Fig. 1. carried a metal collar at its top, through which the brass rod * Abstracted from Poggendorff's Annalen, vol. xcix. p. Fig. 2. 2 inches thick could be moved up to contact with the brass sphere, or withdrawn from it to a distance of 6 inches. The collar was connected by a wire with a general discharging train, and with the same train the rubber of the machine was also connected. On the end of the brass bar a truncated cone of brass was screwed, which is shown in section in fig. 2, and the dimensions of which were ab 81, bc 24, cd 7, and de 1 lines. The conical portion of the piece was at first more complete, but was gradually blunted with great care, until the phænomena now to be described showed themselves. This portion of the work is tedious, but it is indispensable. When the conductor was charged positively by the continuous turning of the machine, the following series of sparks was e d C obtained by the gradual augmentation of the distance between the cone and the sphere. SS Distance of the Electrodes in inches. 11 1층 1호 2 21 3 31 4 45 The continuous passage of sparks took place at the distances marked S; single sparks occurred at the place marked s; and where neither of these letters occur no sparks were observed. Hence in this experiment sparks an inch and 24 inches in length were obtained, but no spark of a length intermediate between those. The pause-distance, as it has been named by Gross, extended to 2 inches, and retained this magnitude almost unchanged in all repetitions of the experiment. When the machine was in very good action, single sparks were observed of an inch in length; but to balance this, none were seen of the length of 2 inches; the pause-distance had, so to say, shifted its position without changing its magnitude. When the electrodes are viewed from a point not too near them in the dark, while they stand at the shortest pause-distance asunder, a very short and slender negative brush is observed at the end of the cone, and on the adjacent surface of the sphere a bluish glowing spot. When the electrodes are gradually separated to a greater distance, the brush remains almost unchanged, but the glowing spot increases considerably in magnitude. If while they remain within the pause-distance the hand or any other conductor be caused to approach the electrodes, the pause is annulled and the sparks pass. When a small plate was fixed about 3 inches below the electrodes, sparks of all the lengths above stated could pass: the pause was not observed. The arrangement of the electricity upon the surface of the sphere, produced by the approximation of the cone, is to be regarded as the primary cause of the phænomenon under consideration. It is known that by the proximity of a conductor connected with the earth, the electric arrangement in an electrified body is essentially changed; so that, theoretically considered, a point of an electrified sphere, for example, may, by the approximation of one unelectrified, be made to assume any density whatever. When the cone connected with the earth is caused to approach the sphere in the above experiments, the nearest point of the sphere assumes the greatest electric density, and from this point all round the density diminishes upon the surface of the sphere, according to a certain law. Let us fix our attention upon the convex surface of a small segment of the sphere (kuppe, calotte), on which the density is not less than that which is necessary to cause the electricity to stream outwards. The density at the highest point, and also the size of this segment depend on the shape and the relative magnitudes of the sphere and cone, and also on their distance asunder. If the cone were a thin sharp point, the density upon the nearest point (9 lines distant) of the sphere must be very great; but the magnitude of the superficial segment alluded to must be very small, inasmuch as M. Riess could observe no light upon the sphere, although the conductor at the same time was losing the greater portion of its electricity. When, on the contrary, the frustum made use of in the experiment stood near the sphere, the density at the highest point of the spherical segment was not very great in comparison with the mean density of the sphere, a fact established by experiment with the torsion balance. The size of the segment must, however, have been considerable, as it appeared luminous on being electrified by the machine. While the density of the segment became smaller as the distance of the cone from the sphere was augmented, the greatest breadth of the luminous segment (an inch) was found by M. Riess, not at the smallest distance of the electrodes (9 lines), but at a distance of an inch and a half. This arrangement of the electricity on the sphere gives the explanation of the pause phænomenon. By the continuous action of the machine, the sphere receives from the conductor a definite amount of electricity in a certain time, and with it a density sufficient for a spark 4 inches in length. If during this time the quantity of electricity delivered by the machine be diminished by streaming into the air, then the density imparted to the sphere suffices only for sparks of less length. The streaming out takes place at all points of the sphere where the density exceeds a certain value, and is the more active the greater is the density. If a sharp metallic point be brought |