is of a deep brown colour, and the salt obtained by evaporation is nearly black. It does not appear to crystallize.

These are all the acids of which I have been able to note the action with the per or deutoxide of manganese. I have followed Berzelius in calling peroxide that one which might perhaps be more correctly termed sesquioxide, as its formula is Mn; but as it is very similar to the analogous oxide of iron, also termed peroxide, and as it is the highest oxide of manganese which forms combinations with acids, it seems best to apply the term of peroxide to this, and super or binoxide to the black oxide of commerce.

If time should favour me, I propose to pursue the above subject, as it is probable that much remains to be determined concerning the compounds of manganese, before we can say with propriety that we are acquainted with the metal.

Philadelphia, May 8th, 1841,

PREPARATION OF CALOTYPE PAPER.

To the Editor.

SIR, Experiments with the papers of Messrs. Talbot and Hunt, described at pages 382-6 of your last November number, led me to the formation of a paper which I think will be found more sensitive to luminous influence than the calotype. An exposure during two or three minutes, at the distance of a few inches or a foot from a single dip candle, suffices to produce a very evident darkening. Should you deem the description of this paper worthy of a place in the Annals, I shall feel honoured by its insertion.

For the sake of brevity, I may state that it is prepared in the same way as the calotype referred to above, with the following exceptions:-The first wash of the nitrate of silver to contain 1.20grs. of that salt to 1oz. of water. The paper so wetted to be quickly dried. Apply the iodide solution to one side only. When the paper is wanted for use, wash it with a solution of ferrocyanate of potash, 100grs.,-1oz. of water: then dip it into rain water. Next apply a "gallonitrate" of double the strength used by Mr. Talbot, and again dip into water. It may be used dry or wet. The impression is brought out by a second wash of the same gallonitrate, but the paper should not be warmed. It is fixed by the use of, firstly, a wash of hyposulphite of soda; secondly, the before-used iodide of potassium. It is better to soak the drawing in the hyposulphite. I am, Sir, Your very

obedient servant,
G. J. T.

P.S. Either the red or yellow prussiate of potash may be employed. I use the latter.

MISCELLANEOUS.

Messrs. Spencer and Wilson's Patent for Engraving by Voltaic

Electricity.

[WE have received a letter from Mr. Spencer in reply to our remarks at page 880, vol. vii, in which, we are glad, to find that the patentees had not been so negligent in guarding against infringements on their patent rights, as, from the tenor of that version of the specification which appears in Newton's "Repertory of Arts, &c.," every reader would be led to suppose..-EDIT.]

Alluding to the specification, Mr. Spencer says, "We state several methods by which the object may be accomplished; but as a type of the whole, we say, that the metallic surface to be corroded is to be connected with one end of a slip of metal or wire, while the other end, is in like manner made to communicate with the negative element or plate of a single pair. A piece of copper or other metal is to be placed opposite the surface required, to be operated on; and it is in like manner made to communicate, by means of a wire, with the zinc or positive element of the same arrangement. This we have illustrated by a drawing, showing how the process is to be proceeded with. The drawing shows two separate vessels, each containing two plates, and letters of reference are on each, in order that all should be legally correct. We also show how the process may be effected, by making the surface to be corroded, or etched, act as the positive element of a single pair, by connecting it with a piece of platinum or other metal, having a less affinity for oxygen than the one to be acted on. Although our specification is not voluminous, we have, in fact, shown every method known, to the public, of performing this process. We have also shown how any number of plates may be etched at one time, and not loose any of their weight, and yet not be in metallic contact with any one of the poles of the battery."

The papers on atmospheric electricity, published in the present volume, were taken from slips of the " Liverpool Albion," and supposed to be sent by Mr. Spencer himself. The following note was omitted:-"The paper was read and discussed, on the evenings of the 22nd and 29th of November of the past year, before the Literary and Philosophical Society of Liverpool. It is the author's intention to publish the whole, in a considerably enlarged form, it being at present very much abridged to suit the time occupied by the evening sitting of a scientific society, as well as the necessarily limited space of the columns of a newspaper. The author's object in the present publication is, that, previously, he may be corrected or justified in his views, by other observers."

On the Employment of a Solution of Bichromate of Potassa in

Voltaic Batteries.

THE bichromate of potassa has been used for a long time by Mr. Mason, of High Holborn, London, in connection with charcoal, in

the production of flame by voltaic batteries; and a solution of this salt has been recently employed by Professor Leeson, in lieu of a solution of sulphate of copper in what is termed the sustaining voltaic battery. The metals of the battery are copper and zinc; the latter amalgamated, and separated from the former by a porous diaphragm. The bichromate solution receives the copper, and a solution of sulphuric acid receives the zinc.

We have not yet heard of any exensive voltaic arrangement in which the bichromate of potassa has been employed; nor, from its great price, is it likely to enter largely into this kind of service. Mr. Mackrell has made a few comparative experiments with twelve pairs of double coppers of the Wollaston form, and amalgamated zinc, in which the latter was amalgamated, and immersed in sulphuric acid solution enclosed in a brown paper case. The liquids in which the copper was immersed were-1st, solution of sulphate of copper; 2nd, solution of bichromate of potash; 3rd, solution of nitrate of potash; 4th, solution of nitrate of soda. All these were saturated. The results of these experiments is said to give a preference to the nitrate of soda, both in the chemical, magnetic, and calorific cl es of phenomena. We do not see this verified by the list of res. The sulphate of copper was most active at first, and the bichromate of potash appears to be second in the list, and the nitrate of soda the least active of the whole and it was not until the expiration of two hours and twenty minutes that the nitrate of soda had any advantage; and what appears singular enough, in Mr. Mackrell's experiments, the battery used with this salt is stated to have an improved action up till four hours and twenty minutes, at which time it produced three cubic inches of gas per minute, from acidulated water, although it only produced '92 of a cubic inch at the end of the first eight minutes!!! The quantity of gas liberated by the sulphate of copper battery was only four cubic inches per minute for the first quarter of an hour; and the whole quantity in four hours' work, is twice that by the bichromate battery, and about two and a half times that given by the employment of the nitrate of potash or the nitrate of soda. In the magnetic and calorific effects, also, the sulphate of copper has a decided preference, for the first hour, at least; but the table of results is far from showing a regularity of action.

[NOTE. It may be interesting to many of our readers to be informed, that we have found pencils of coke or cinder far superior to any other article in the production of light by voltaic action; and to prevent patent dabblers from taking advantage of it, we at once recommend it, either separately or in conjunction with other matter, as a source of illumination for both general and particular purposes. With a series of six pairs of cast-iron and amalgamated zinc, we make a massy piece of iron dance in a coil carrying the current.EDIT.]

ANNALS OF ELECTRICITY &c. VOL. VIII. PL 2.

M'Joule on the Electric Origin of the Heat of Combustion.