rictional, has been the great drawback on their being more extensively used by the faculty.

Seventh. The great portability of my machine makes it very convenient for travelling, as there is a mahogany case which slides upon m against b, where it locks at n; there is a closet in the case, into which all the apparatus, figg. 2, 3, 4, 5, pack. EDWARD M. CLARKE, Magnetician.

No. 9, Agar Street, West Strand, London.

LV. On the Iodides of Gold. By JAMES F. W. JOHNSTON, Esq., A.M., F.R.S.E., &c. &c., Reader in Chemistry and Mineralogy in the University of Durham.*

WH

I. Proto-iodide of Gold. Au + I.

HEN iodide of potassium in solution is added in excess to a solution containing terchloride of gold, a precipitate is obtained of a greenish yellow colour, while the supernatant liquid becomes dark-coloured from the excess of iodine held in solution. If the terchloride be in excess, the precipitate has a blueish gray colour, being a mixture of the yellow powder with iodine, or with the teriodide of gold. If the precipitate be heated in the dark-coloured mother liquor, it diminishes in quantity, and on cooling gradually separates in minute golden yellow crystalline scales of great beauty, exhibiting apparently triangular and square faces, and not inferior in lustre to iodide of lead crystallized from a similar hot solution.

This beautiful yellow compound consists chiefly of protoiodide of gold. According to the analysis of Pelletier (Ann. de Chim. et de Phys., vol. xv. p. 116) it contains 34 per cent. of iodine. Exposed to the air and light, it is gradually decomposed, and more readily when moist, giving off iodine. At 150° Fahr. it begins to give off iodine; at 230° Fahr., it undergoes almost total decomposition, losing only one per cent. additional when heated to 400° Fahr. Two portious prepared at different times, lost when decomposed by heat, 33.96 and 34.43 of iodine respectively. After exposure to the air for ten days it lost only 9.6 per cent.

A compound of one atom of gold with one of iodine should contain 38.83 per cent. of iodine. The low temperature at which the compound is decomposed rendering it probable that the crystallized portions analysed by Pelletier and myself might contain metallic gold, I collected first a heavier brighter portion which collects at the bottom when the precipitate is heated in the mother liquor: it lost when dried and heated

* Communicated by the Author.

valleys which stretch between the Kyárda-dún and the valley of Pinjór, in the Siválik or sub-Himálayan belt of hills, associated with bones of the fossil Elephant, Mastodon, Rhinoceros, Hippopotamus, &c. So far as our researches yet go, the Sivatherium was not numerous. Compared with the Mastodon and Hippopotamus (H. Sivalensis, Nobis, a new species characterized by having six incisors in either jaw,) it was very rare.

Northern Doáb, Sept. 15, 1835.

LVIII. Observations on the Construction of Voltaic Batteries; with a Description of a Battery exhibited at the Royal Institution of Great Britain, June 3, 1836, in which an uniform and powerful current is sustained for any period required. By FRED. WM. MULLINS, Esq., M.P., F.S.S., &c.*

HAVING for some years devoted all the time I could spare

from other avocations to researches in voltaism and electro-magnetism, I frequently experienced considerable inconvenience from the impossibility of keeping up an equally powerful current of electricity for a period sufficiently long to answer my purposes; and in one particular instance, which I shall more especially refer to in a future paper, as connected with a very important discovery, the obstruction to the inquiries I was then making was so great, that I resolved, if possible, to conquer the difficulty, and conceived that notwithstanding the disappointments that had previously attended similar attempts, some means might still be discovered by which those consequences of chemical action on the metals employed in the galvanic circuit, and which Sir Humphry Davy and other distinguished philosophers had decided to be the chief cause of the decline of electric power, might be prevented, or, at all events, considerably diminished. I therefore commenced a series of experiments on this subject, in the course of which it struck me that a conducting substance interposed between the two metals would effectually protect both metals from the injurious effect of the gases and oxides formed while the battery was in action, while the electric current would find a free passage, and a surface of copper, or whatever other metal performed its functions, in the fittest state to receive it from the electrolyte. I had been previously in the habit of using membranous substances as conductors of voltaic electricity, in a course of experiments in which I had been engaged with the view of obtaining a new mode of developing voltaic power; and having found that thin membranes, when moistened in alkaline or acid solutions, af

Communicated by the Author. An abstract of Professor Daniell's paper on the Constant Voltaic Battery, recently constructed by him, will be found in our last volume, p. 421.

forded a free passage to the electric fluid, I concluded that my object would be fully attained by their employment in the voltaic circuit. I accordingly prepared a very thin calf's bladder, and having placed in it a coil of thin sheet copper, with a small quantity of solution of sulphate of copper, I immersed both in an earthenware pot containing a cylinder of zinc fitting close to its inner surface, and distant from the surface of the copper an inch and a quarter, and a sufficient quantity of diluted sulphuric acid, in the proportion of 5 of the acid to 100 of water; and on testing the power of this battery with the voltameter, I found that the first deflection suffered very little diminution for several hours, though I had made no alterations in the fluids used, nor in any way disturbed the arrangement (in this experiment the pot used was only two and a half inches in diameter and three deep). In a second experiment, made with the same battery and with the same solutions, having connected it with an electro-magnet of the horse-shoe form, four inches in length and five eighths in diameter, the magnet sustained 50 lbs. attached to the keeper for three hours. Having thus proved the possibility of obtaining a continuous and equally powerful current for a long period, it next became a question whether the power could not be still further increased and prolonged by the use of other conducting liquids in contact with the same quantity of metallic surface; and after a long course of experiments upon the nature of chemical action on metals in voltaic connexion, and the comparative effects of different electrolytes of different degrees of strength, the results of which I consider sufficiently important to form the subject of another paper,-I found that of the various acid, alkaline, and saline solutions tested, muriate of ammonia in the proportion of 5 parts of the saturated solution to 100 of water, gave me the best conducting fluid, combined with the least injurious action on the zinc surface; in fact, so slight that, after several days of constant action, the zinc plate, which was amalgamated, was scarcely corroded or reduced in thickness.

It next became important to examine what connexion existed between the power produced and the distance between the zinc and copper; and it appeared natural to conclude that the more remote the surface of the copper from that of the zinc, the less would be the effect produced on completing the circuit; but, as I was aware that great diversity of opinion existed upon this subject, with the view of fully satisfying myself with respect to the best mode of construction of voltaic batteries, I prepared an apparatus by means of which I was enabled most accurately to measure the increase or diminution

Teriodide of Gold with Iodides of Sodium and Ammonium.— These salts are prepared by digesting solutions of the respective iodides on the teriodide. They both crystallize in black four-sided prisms, having much lustre, those containing ammonia being generally flattened. They are both deliquescent, that of sodium so much so that it is obtained in crystals with great difficulty; that of ammonia only in a moist atmosphere. I have not ascertained whether or not they contain any water of crystallization.

The teriodide dissolves also in solutions of the iodides of barium and strontium, giving similar dark-coloured solutions. A solution of the iodide of iron likewise takes it up in considerable quantity, and forms with it a crystallizable compound.

The solution in hydriodic acid has the same dark red colour. Set aside to spontaneous evaporation, it deposits minute black prisms, which, on exposure to the air, acquire a beautiful purple tint, probably from loss of iodine. Whether these are merely crystals of the teriodide, or a compound with hydriodic acid, I have not ascertained. The former is the more probable.

The

Like the solutions of the terchloride, those containing the teriodide are also decomposed by the addition of caustic ammonia. The precipitate is of a brown colour, more or less dark, sometimes almost black, and, like fulminating gold, it detonates when heated, giving off iodine and ammonia. dark precipitates are obtained by pouring liquid ammonia into an excess of the teriodide; the lighter, by dropping a solution of the teriodide into caustic ammonia, and agitating at each successive addition. They are decomposed by hot nitric acid, evolving iodine, and leaving a mixture of proto-iodide and metallic gold.

Durham, August 30, 1836.

LVI. Experimental Researches into the Physiology of the Human Voice. By JOHN BISHOP, Esq., &c. &c.

[Continued from p. 209.]

THE lungs having been supplied with air by the muscles of inspiration, the ligaments of the glottis are drawn into the vibrating position.

The air in the chest and trachea being now condensed by the muscles of expiration, a portion of the glottis yields to its pressure, and the edges are curved upwards so as to be nearly parallel to the axis of the vocal tube, leaving between them an aperture through which the air passes. The tension and elasticity of the vocal ligaments tend to restore them to the plane

of the vibrating position, whilst, at the same time, the air is acting in an opposite direction.

The vibration of the edges of the glottis thus produced, by communicating to the adjacent air an alternate state of condensation and rarefaction, the sounds of the voice are accomplished.

The relative length of the vibrating surface of the glottis is regulated conjointly by the pressure of the column of air in the trachea, and the tension and resistance of the vocal liga

ments.

A certain degree of condensation of the air is therefore requisite, the maximum varying with the proportion of the area of the chest to that of the trachea. It is upon these hydrostatic principles that the small muscles which close the glottis are capable of resisting the whole force of the respiratory muscles*.

If a person possessing a deep bass voice be directed to expel his breath in a manner not quite sufficient to yield the lowest possible note, on applying the ear to his mouth a clicking motion is perceived. If the tension and velocity of the air are now increased, the clicking ceases, and a continued sound is produced, but of an exceedingly grave pitch. During the previous state, Dr. Young+ observes, "a delicate ear may detect the vocal chords vibrating twenty-six times in a second, or about two octaves below the A of a common bass voice."

The intensity of the voice in the same medium‡, and under similar collateral circumstances, depends on the pressure of the column of air in the trachea, and the range of motion performed by the vibrating edges of the glottis.

The true vibrating surface of the glottis is the mucous membrane. The vocal chords confer on it the tension, resistance, position, and probably other conditions necessary for vibration. Aphonia often results from undue relaxation of this membrane.

When we consider the fundamental pitch of the human voice, and compare the length of the vocal ligaments with that of stringed instruments, or the length of the vocal tube with that of wind instruments, we must at once perceive that the

*The force of the expiratory muscles is about a pound on every square inch of the surface of the chest.

+ Nat. Phil., vol. ii.

Acording to Derham, the human voice has been heard at the distance of ten miles at Gibraltar. Boussingault, in his ascent of Chimborazo with Colonel Hall,'at the height of 6004 metres, found the voice scarcely audible. inhaling hydrogen gas also greatly enfeebles the voice. The intensity of the tone varies reciprocally with the density of the air under similar collateral circumstances.