known, and, indeed, all circumstances accord in pointing out this as the principal source of the heat evolved.

A striking confirmation of the explanation now given of these exalted effects of common and alloyed zinc, is derived from an investigation of their power of forming voltaic combinations of more or less intensity. Being combined two and two, and examined by the galvanometer, it was found that the order was as follows: distilled zinc, lead zinc, tin zinc, iron zinc, zinc of commerce, and copper zinc: thus arranged, the most positive are first, or each is positive with those following it, negative with those preceding it. When combined into voltaic pairs with copper, distilled zinc, lead zinc, and tin zinc, were most powerful, then zinc of commerce, and iron zinc ; copper zinc was last, and very inferior to the rest. It appears, therefore, that the kinds of zinc which exhibit least action in diluted sulphuric acid are those which form the most powerful voltaic combinations with such metals as copper, silver, platina, &c., and this might be expected: for the disengagement of hydrogen on the surfaces of the zincs does not arise from a direct chemical action, but from the action of the minute electric currents established between the molecules of the zinc and the heterogeneous metal present in it; whereas the current, sensible to the galvanometer, is produced by the direct action of the acid on the positive element of the pair of plates used. This direct action is stronger on the pure zinc than on the zinc mixed with less oxidable substances; and the less these heterogeneous substances are oxidable, the less positive should the zinc be*. This distinction will probably explain many apparent

Is not the diminished power of the alloys in forming voltaic combination with more negative metals due rather to the circumstance of their finding the negative element ready for them, under more favourable circumstances, than that which, in the form of a copper plate or platina wire, is purposely added by the experimenter; than to any material diminution of the direct chemical action? The heterogeneous metal originally in the zinc forms a voltaic combination with it, having great extent of surface, because of its minute division, in excellent contact, and at the smallest possible distance; and therefore must divert the course of much of the electricity which in pure zinc finds its exit into the fluid only by the negative element purposely added.

We refer our readers to a similar effect to the above remarked by Messrs. Stodart and Faraday, in their paper on alloys of steel, and which they also referred to voltaic action. 'If two pieces, one of steel, and one steel alloyed with platina, be immersed in weak sulphuric acid, the alloy will be immediately acted upon with great rapidity, and the evolution of much gas, and will shortly be dissolved, whilst the steel will be scarcely at all affected. In this case it is hardly possible to compare the strength of the two actions. If the gas be collected from the alloy, and from the steel, for equal intervals of time, the first portion will surpass the second some hundreds of times. A very small quantity of platina alloyed with steel confers this property upon it; increased the action considerably; with and To it was powerful; with 10 per cent. it acted, but not with much power; with 50 per cent. it was about equal to steel alone.' These alloys were very perfect; that which was most active in acids did not render a platina wire more negative than ordinary steel, and the cause, as was suggested at the time by Sir H. Davy, is referred to electrical action, the view taken being described at length in the paper in the Phil. Trans. for 1822, p. 262.

anomalies, and serves to show how difficult it is to judge of the true intensity of chemical action exerted upon a substance by liquids in contact with it *.

19. CRYSTALLIZATION OF BISMUTH.

M. Quesneville, fils, says, that by the following process, magnificent crystals of this metal may be obtained. Bismuth is to be fused in a crucible, fragments of nitre added from time to time, and the heat raised so as to decompose the nitre, and the whole mixed by agitation. Continuing the heat and the addition of nitre in this way for some hours, a time arrives when a little of the metal agitated in the air exhibits magnificent green and golden-yellow colours, which it retains when cold. If the metal displays only rose, violet, or indigo colours, and when cold is a white mass without colour, it is certain that good crystallization will not occur. When the metal is in right condition, it is to be poured into a ladle previously heated; and to prevent the surface cooling faster than the bottom, it should be covered, or a hot shovel held near it. The cooling should not be too slow, for then the metal crystallizes layer by layer, and offers no fine forms; it is necessary that the cooling be rather sudden. When the upper crust has formed, it should be pierced by a hot coal, and not by percussion (which disturbs the crystals), and the remaining liquid metal decanted. In about half an hour longer the rest of the crust may be broken, and the interior will be found magnificently crystallized, the crystals being more beautiful as the above conditions have been more carefully followed t.

20. ON DISCOLOURED CHLORIDE OF SILVER.-(M. Cavalier.) Chloride of silver blackened by sun-light is perfectly well known. M. Cavalier obtains it in a similar state by dissolving the recent chloride in ammonia, and passing chlorine gas into the solution; the usual decomposition of ammonia with elevation of temperature, evolution of azote, &c., takes place, and ultimately the liquid becomes turbid, and the chloride of silver appears first as a grey, and then, when the ammonia is entirely decomposed, as a violet precipitate.

This precipitate dissolves entirely in ammonia, and is precipitated in a perfectly white state by pure nitric acid. If 20 grains of it be decomposed by zinc in dilute sulphuric acid, it yields 15 grains of silver, exactly the quantity yielded by similar treatment from 20 grains of white chloride. Hence the difference of the chloride in these two states cannot be referred to difference of composition, but solely to some variation in molecular arrangement ‡.

Bib. Univ. 1830,

p.

391.

Jour. de Pharmacie, 1830, p. 554. Jour. de Pharmacie, 1830, p. 553.

21. COMPOSITION OF FULMINATING GOLD.

M. Dumas has analysed the fulminating gold prepared by precipitating solution of chloride of gold by ammonia, the process adopted being that of burning it with oxide of copper. He found 100 parts to yield

Metallic gold
Nitrogen
Chlorine

73.00

9.88

4.50

87.38

by further experiment and reasoning, it was deduced that there were besides, 2.2 parts of hydrogen and 10.42 of oxygen. These elements are considered as being thus arranged:-gold 73; azote 5; ammonia 6; chlorine 4.5: water 11.5; and the proportions of the ultimate elements are given as 6 atoms of gold; 12 of azote; 2 of chlorine; 42 of hydrogen; and 9 of oxygen. It is finally viewed as a compound of 2 atoms of ammoniacal azoturet of gold, and 1 atom of ammoniacal subchloride of gold, with enough water to convert the azote into ammonia, and the gold into oxide of gold.

Oxide of gold digested in ammonia forms another fulminating compound. This compound analysed gave 2 atoms of gold; 4 of azote; 12 of hydrogen; 3 of oxygen *.

22. WHEWELL'S WRITTEN NOMENCLATURE FOR CHEMICAL

COMPOUNDS.

Extract from Professor Whewell's Essay on Mineralogical Classifi cation and Nomenclature :

Professor Whewell's mode of designating the combinations of chemical elements is different from that of Berzelius and of Beudant, but the alteration seems to be absolutely necessary. According to their method, the first combination of elements into binary compounds is indicated by writing the symbols together, without any connecting sign; as if they were algebraically multiplied: and the number of atoms of each element is denoted by figures, written as indices

of powers generally are. Thus, C+ 2 they would represent by Cc, and 3C + 2S by C S2, &c. Now this notation is in the highest degree inconvenient, besides violating all symmetry and analogy.' For when the substance is indicated by 2 AS + CS, there is no

2Ä

longer any obvious identity with 2 A+ 3C + 4S, which is the real result of the analysis.

Ann, de Chimie, xliv. p. 167.

Alum KS2+2ÄS2+48· Aq 2·(Ä+3S)+K+2S+48 : Aq.

Coefficients are, in all cases, used instead of indices.

23. PARA-TARTARIC ACID.

M. Dulong read to the academy a letter from M. Berzelius, relative to numerous chemical compounds, which being similar in the nature and proportion of their elements, yet differ in property from each other. M. Berzelius had been particularly engaged with the acid found in tartar by M. Gay Lussac, which has been called Vosges acid (Thannic acid.) He shows that this acid, though differing from ordinary tartaric acid in many properties, has exactly the same composition.

Similar difference in properties without difference of composition is found in phosphoric and pyro-phosphoric acid; in stannic acid or deutoxide of tin, obtained from tin by nitric acid, or obtained from Libavius liquor by precipitation.

To associate and yet distinguish substances under these peculiar circumstances, M. Berzelius proposes to prefix the Greek term para to the name of that body which occurs most rarely, or which is obtained with the most difficulty, thus:-Phosphoric acid, and paraphosphoric acid; tartaric acid, and para-tartaric acid; stannic acid, and para-stannic acid, &c.*

24. PREPARATION OF PIPERIN, BY MR. CLEMSON.

The pepper should be ground and digested in alcohol of specific gravity 0.832, or 0.817 at a smart distilling heat; an alembic, with its water bath, is at once convenient and economical; the whole should be agitated from time to time, and the fluid changed if necessary. I know of no better indication of the entire extraction of the piperin, than the want of taste in the marc or insoluble residue; although acridity (as has been represented) is by no means a property of piperin. The alcoholic solutions being united, should be reduced over a water bath. The distillation ended, there will be found in the bottom of the alembic a deposit composed of a great deal of piperin, and a black acrid resino-oleaginous substance; the separation of this latter compound from the piperin is difficult in the extreme; so much so, that I have seldom or never seen the preparation free from acridity, which not only destroys, but produces a contrary effect to that desired, when employed as a remedy. The greater part of this viscous oil may be separated by cold alcohol, piperin being much less soluble in

* Jour, de Pharmacie, 1830, p. 622,

this menstruum, when cold, than when warm, and much less than the oil. The latter portion may be entirely separated by the addition of a little lime to the warm solution of piperin with the oil, and leaving it to crystallize in the same vase; the piperin, when cold, may be separated at leisure: by re-dissolving the crystals thus procured, adding a little animal charcoal, and filtering when hot, a solution will be obtained, which, upon cooling, will afford crystals of a canary white, regular and free from acridity. Mr. Pontel has advised the use of caustic potash, and the effect is certainly very marked. The solution should be weak, for caustic potash has a tendency to alter the nature of the substance, and instead of procuring piperin, I once formed a compound that very much resembled soap, and all subsequent attempts to procure the substance in crystals failed; moreover, I have always observed, that those crystals obtained by the aid of potassa had more or less of a reddish tinge, and were very brittle. Piperin, when pure, crystallizes in right square prisms, occasionally presenting an anomaly, the crystals, particularly those obtained through the means of potassa, being hollow, or containing an interior decrement, the four vertical sides being entire, and showing the form of the crystal; they are insoluble in water, soluble in cold alcohol, and more so when warm; insoluble in acetic or other acids. Piperin has been employed latterly in Italy as a febrifuge*.

25. ON SALICINE BY MM. PELOUZE AND JULES GAY LUSSAC. Salicine, when pure, forms white crystalline prismatic needles. It has a bitter taste and somewhat of the odour of willow bark. One hundred parts of water dissolve 5.6 parts of salicine at 67° F.: at 212° F. it appears to dissolve in any proportion. It is equally soluble in alcohol, but ether and oil of turpentine take up no portion of it. Concentrated sulphuric acid gives it a fine red colour, like that of bichromate of potassa. Muriatic and nitric acids dissolve it without producing any colour. It is not precipitated from its solution by infusion of nut-galls, gelatine, neutral or subacetate of lead, alum, or emetic tartar. It does not saturate lime-water when boiled with it in excess it does not dissolve oxide of lead: it fuses a little above 212° F., losing no water, and crystallizes upon cooling. If the heat be rather higher, it acquires a lemon-yellow colour, and becomes, when cold, brittle as resin.

Salicine, burnt by means of oxide of copper, yields a gas entirely absorbable by potash. The mean of two analyses gave the following as its composition:

Carbon
Hydrogen

55.491 2.028 proportions.

Oxygen. 36.325 1.000

Its composition may, therefore, be represented by two volumes of olefiant gas, and one volume of oxygen †.

* Silliman's Jour. xvii. p. 253.

Ann. de Chimie, xliv. p. 220.