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resinous electricity, others charged with vitreous electricity, and intermediately some neutral spaces, which are the bright ones. The limits of these transparent clouds may be found by means of a kite or a balloon.

18th. The condensation of these transparent clouds forms secondary opaque clouds charged with their respective electricities. A new elevation in the temperature produces a new division in the electric charges. The first vapours produced are more resinous than the preceding ones, the last are less so; they are vitreous in relation to the superior vapours and resinous in relation to the inferior. It is after these successive condensations and evoporations that the superior vapours acquire stronger and stronger resinous tensions, and that those near the ground become more vitreous. Intermedi. ately there are some of different degrees, which are maintained separate by the difference of their specific weight.

19th. In proportion as the vapours, by this series of transformations, are charged with an increasing electricity, their molecules repel each other: they are also more repelled from the earth or attracted towards space; and they rise to heights greatly superior to those which correspond to their specific weight. These opaque or transparent clouds, charged with different degrees of resinous electricity, (some of which in relation to the tension of the globe, which serves as a standard, are resinous, and others vitreous,) neutralize each other when they approach, in consequence of the condensations which the depressions of temperature and the diminished terrestrial repulsion cause them to undergo. When there are other strata of clouds interposed, exchanges are made, which vary with their mode of agglomeration and their conduction. These exchanges produce sudden explosions if the margin of the clouds contains much free electricity; or rather continuous explosions if the conduction is feeble, and if the discharge takes place along the contiguous masses.

20th. A discharge at one point being followed by a new equilibrium, occasions others; it is thus that meteors succeed each other, and may become numerous at certain epochs; it is thus that simultaneous meteors which succeed each other at short intervals are observed in countries distant from each other, meteors which have been frequently taken for the same, on account of the apparent simultaneousness of their existence.

21st. After these restorations of equilibrium, or electric discharges, the vapours being less repelled, gravity regains its proper influence; they descend, become condensed, and at last dissolve into rain.

22nd. Rain proceeding from resinous clouds is more abundant than that proceeding from vitreous clouds; the winds are likewise more sudden and violent, and it is under the induction of masses of resinous clouds that tempests and inundations arise.

On certain Delineations produced by Electricity. By G. KARSTEN. In the 6th volume of the "Reportorium der Physik." VEITH, Berlin. Translated by W. G. LETTSOM, Esq.

[From "Poggendorff's Annalen," vol. lvii. p. 492.]

[1842, page 180.]-DR. RIESS describes a species of electrical figures to which he gives the name of "electrical breath figures." My method of obtaining these figures in the most perfect state, is to charge a Frankin's table, one of whose coatings was moveable, and then to discharge it after that coating was removed; as in that case the figure that had been observed on the passage of the fluid was again revived, on the plate being breathed upon. Certain places on the plate had therefore had impressed upon them the property of not becoming wetted on exposure to aqueous vapour. The analogy existing between these figures and the pictures produced by Moser, struck me so forcibly, that I instituted experiments for the production of the latter figures by means of electricity. For this purpose I laid a coin on a piece of plate-glass, which in its turn rested on a metal plate in connection with the ground, and then let sparks from the conductor of the machine fall on to the coin, from which they instantly darted off to the metallic plate. After 100 turns of the machine, the plate of which is 20 inches diameter, I removed the coin the plate of glass appeared to have undergone no change whatever; but upon breathing on it there was seen an impression of the coin, perfect in its minutest details**

The following questions now arise:-Is the image that is thus called forth produced by traces of electricity still adhering to the plate of glass? Has it been caused in a similar manner to those of Moser, that is to say, by light? Can similar images be obtained likewise upon metal? What are the conditions for obtaining these pictures with success? In what way can they be fixed?

The first of these questions I must answer decidedly in the negative: immediately after it is electrified, the plate, it is true, does manifest a trace of electricity; by wiping it, however, with a cloth, or by letting it stand for a considerable time, this trace of electricity disappears altogether, yet the image is given with great precision; indeed even though the plate is well rubbed, warmed, and breathed upon, it is a hard matter to get rid of all traces of the image, and this indeed is often troublesome in performing the experiments. Another argument against the supposition that a trace of electricity can be still adhering to the plate is this, namely, that the picture is not weakened or effaced on directing the opposite electricity on to it; besides, both kinds of electricity produce precisely similar effects.

* I can bear out this from actual inspection, with the addition that on looking through these breath-figures, the raised parts of the coin correspond with the darker portions of the image, whereas on looking down into them, the reverse is the case.-Edit, of the Annalen.

What however is quite decisive upon this point is, the circum-stance that (by observing certain precautions that I will explain directly,) I have also obtained these images on polished metal plates, in which there can be no question of any adhering electricity. The actual presence of electricity is therefore not the cause of these images.

It cannot be so readily decided whether their origin is due to causes similar to those that develop Moser's picures, or whether they are to be attributed to a peculiar influence of electricity. What militates against the first of these views is, that the process is completed in an extremely short time compared with what is required for the production of Moser's pictures; a few turns of the machine suffice for impressing the outlines of the medals on the glass, and the time that is required for 300 turns, thus giving the quantity of fluid required for the production of images on metal plates, is comparatively speaking, only very limited.

But to this it may perhaps be objected that the intensity of the light is so considerable, that this short time is sufficient for producing the picture. To this we may reply, that shocks from a battery, the light from which is beyond all question considerably brighter than that of sparks, do not produce so distinct a picture as sparks do. Besides, I insulated the medal by means of sealing-wax, and retained it at the distance of a line from the glass, so that the sparks passed over at once from its edge on to the plate of metal; yet, nevertheless, I obtained an image, and this without there being, even in the dark, any visible display of light whatever between the medal itself and the glass plate.

There would be thus nothing left for us but the so called dark or invisible rays of light; but even these do not, that we are aware of, produce such intense effects as those in question, and we should therefore be forced to assume that in the electrical light or electric fluid there is a marked and special abundance of that species of rays which induce those superficial changes of which we are here treating. As there is at present, however, no ground for such an assumption, we must, as the matter now stands, attribute the effect in question to some peculiarity in electricity.

With respect to the conditions to be observed for insuring success with these pictures, what I have been able to ascertain with certainty up to this time is as follows. First. A good deal appears to depend upon the quality of the glass; the pictures are produced with equal distinctness on thick and on thin glass excepting when coins are applied to both sides of the plate, in which case they act as coatings. With thin glass many plates may be laid upon each other, and on each there is given a recognizable impression of the medal, though indeed gradually becoming lest distinct. Difference in the chemical composition of the glass produces a marked difference in the pictures, for, other circumstances being alike, I have obtained pictures of very unequal goodness upon glass of different composition. It

appears to be immaterial whether the knob from the conductor is brought into contact with the coin, or whether the sparks strike down on to it. The sharpness of the impression is, on the other hand, very materially increased when the sparks strike off freely from the coin into the external plate of metal; and in those cases where the fluid escaped, slowly, from the medal, the images were indistinct.

The best images that I obtained on metal plates I got when I laid a piece of oiled paper between the plate and the medal, by which means the transmission of the electricity was somewhat retarded; images were however also produced when the medal was in immediate contact with the plate. I cannot take upon myself to say for certain that the nature of the metal of the coin itself has an influence in the matter, but it appeared to me that those composed of the best conductors produced the clearest images. As has been already remarked, strong shocks from a jar or a battery do not bring about the same effects as single sparks, at least with a battery one must give quite as many turns of the machine (and with a jar indeed more) to obtain a picture of equal precision. There may be several reasons for this, partly from a residual charge remaining both in the jar, and also in the battery, and this causing a diminution in the actual amount of electricity imparted; partly also from the effect of the machine being lessened the nearer the jar, or the battery approaches to a charged state. Positive and negative electricity appear to be equally effective in their results, but I have not yet performed experiments enough to settle this point.

With regard to fixing the pictures, I have, as yet, succeeded but very imperfectly on this head. The pictures upon the plates of glass were, it is true, developed by an exposure to the vapours of mercury and iodine; they, however, disappeared as soon as they were removed from the apparatus. The pictures on the metal plates, on the other hand, were fixed by the iodine and mercury vapours, not however uniformly or with distinctness; this, however, may be owing party to a want of dexterity in the manipulation, and partly to the faulty construction of the apparatus.

From the necessity of interposing an imperfect insulator when obtaining the most satisfactory results upon metallic plates, it occurred to me to try to produce pictures by means of the galvanic current; as yet, however, I have not by this means obtained more than the trace of an impression. There is no doubt however that successful results will follow from a suitable modification of this process. Should the continuation of my experiments lead to further results, I will not fail to communicate them to you.

On the Determination of Azote in Organic Substances by the Process of Messrs. Varrentrapp and Will. By M. REISET.

M. REISET has submitted the new process of analysis of MM. Varrentrapp and Will to a careful examination, with the view of

ascertaining how far it may be relied upon as a means of correctly estimating the quantity of azote contained in organic bodies. He says, the fundamental conditions essential to place the new method of analysis beyond all objection, are, first, that the whole of the azote contained in the azotised substance shall be transformed into ammonia; and, secondly, that the azote of the air contained in the combustion tube, shall not, in any case, contribute to the formation of ammonia. The experiments of Berzelius, and more recently those of Varrentrapp and Will, have shown that the first of these conditions is completely fulfilled. All azotised substances, with the exception of those containg ozote in the state of nitric acid, transform the whole of their azote into ammonia under the influence of the alkaline mixture, at an elevated temperature. The combinations of cyanogen even, furnish ammonia as easily as a mixture of sal ammoniac and lime.

With regard to the possibility of the formation of a certain quantity of ammonia at the expense of the atmospheric air contained in the tube, MM. Varrentrapp and Will have made the following experiment to meet this objection. A mixture of azote and hydrogen, such as arises from the decomposition of ammonia by copper, was passed, at a red heat, 1st, over a mixture of calcined cream of tartar and lime; secondly, over a mixture of recently prepared lamp-black and calcareous soda; and thirdly, over the simple mixture of lime and soda. In none of these cases were they able to detect the least quantity of ammonia formed.

This experiment was considered sufficient, by these authors, to establish the accuracy of the indications afforded by their process, and any excess of azote which may appear in the result of the analysis, they ascribe to impurities in the substance analyzed, or in the chloride of platinum.

These conclusions appear to me not to be sufficiently established, for although a mixture of azote and hydrogen produced no ammonia under the circumstances of MM. Varrentrapp and Will's operation: does it therefore follow that a non-azotized substance, or one very rich in carbon, when burnt with the alkaline mixture in contact with atmospheric air, never yields ammonia?

This question was rendered the more interesting, in consequence of the announcement, some time ago, by Faraday, that non-azotized substances, such as sugar, acetate of potash, oxalate of lime, tartrate of lead, &c., when calcined with hydrate of potash, of soda or baryta, always afford a sensible quantity of ammonia. It is evident, on reading the paper of this able chemist, that the re-agents employed by him were perfectly pure, having been prepared by himself with great care.

It remained to be determined with accuracy whether the facts observed by Mr. Faraday might have some influence on the results of the process of analysis of MM. Varrentrapp and Will.

The following experiments appear to me to leave no doubt on this point:

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