Page images
PDF
EPUB

sulphate and sulphuret of lead, of oxyd of antimony, and sulphuret of antimony, which we cannot here detail, Mr. Smithson proceeds to consider the geometrical form of the triple sulphuret.

Of the 17 figures given of this mineral by Count Bournon, in the second part of the volume of the Transactions for 1804, Mr. Smithson considers none as consistent with nature. The primitive form of this mineral is said, in the account quoted, to be a rectangular tetrahedral prism; but according to Mr. Smithson's measurement it is cubic. In demonstrating the truth of this assertion, Mr. Smithson pays little respect to the well known abilities of. Count Bournon, with whose skill in the field of mineralogical science the world is well ac quainted. The tenor of this part of Mr. Smithson's paper is. certainly not becoming a philosopher of his general respectability. Part of the errors into which the Count has fallen are owing to his being a follower of De Lisle, who, being ignorant of the mathematical calculus used by other crystallographers, was sometimes led to assume a fundamental form, different from that which the superior geometrical knowledge, of Hauy has shewn to be the primitive form. We were much surprised to find in Mr. Smithson's paper such a barbarism as "powder of Algaroth."

IV. On Oxalic Acid. By Thomas Thompson, M. D. F. R. S. Ed. Read, Jan. 14. 1808.

The principal object of this elaborate essay is to shew the great benefits which may be derived from the theory of Dalton, with regard to the modes of ascertaining the relative weight of the elementary particles of compound bodies by arithmetical calculations, and to point out its application to chemical science and to the practical operations of the laboratory. In the present instance, Dr. Thompson has very ingeniously applied this mode of analysis to the chemical examination of oxalic acid, and its combinations with different bases.

After having established the relative proportions by weight of the elements that enter into the composition of oxalic acid, Dr. T. observes, that the knowledge of these, though important, is by no means sufficient to convey a clear idea of this compound. It does not shew in what respects this acid differs from other vegetable acids, from alcohol, from sugar, and from various other bodies possessing very different properties, although they are composed of the very same ingredients, arranged only in different proportions. Hence the number of the elements that enter into the composition of the body must be determined by arithmetical or algebraic computations, in

order to form a true notion of its constitution. Numerous and decisive experiments have proved that elementary bodies always enter into combinations in determinate proportions by weight, or in multiples of them; and these may be represented by numbers. Namely, the numbers which correspond to the 4 elements, oxygen, azote, carbon, and hydrogen, and which are the following: oxygen 6; azote 5; carbon 4, 5; hydrogen 1. In all compounds consisting of these materials, the proportions of the different constituents may always be represented by these numbers, or by multiples of them. Thus: water consists of 1 part, by weight, of hydrogen, and 6 of oxygen; each particle may therefore be considered as composed of one atom of hydrogen, united to one of oxygen. Carbonic oxyd, which contains 4, 5 in weight of carbon, and 6 of oxygen, is composed of 1 atom of carbon, combined with 1 of oxygen. Whereas carbonic acid, containing 4, 5 in weight of carbon, to 12 of oxygen, has 2 atoms of oxygen united to 1 of carbon. Carburetted hydrogen has 2 of oxygen to 4,5 of carbon. Olefiant gas, hydrogen to 4,5 carbon. Nitrous gas, contains 5 in weight of azote, to 6 of oxygen. Nitric acid, 5 of azoté, to 12 of oxygen. Nitrous oxyd, 10 of azote, to 6 of oxygen.

From the knowledge of this curious law, it is difficult to avoid concluding that each of these elements consists of atoms of determinate weight, which combine according to certain fixed proportions, and that the numbers above given represent the relative weights of these atoms respectively. Thus, an atom of oxygen weighs 6, an atom of hydrogen 1, &c. Water is composed of one atom of oxygen, and one of hydrogen; carbonic acid of two atoms of oxygen and one of carbon, &c. This theory belongs to Dalton. The paper before us affords numerous examples in illustration of the atomic gravity of various saline bodies; and the same law, it is perhaps needless to state, holds good with respect to other bodies. Numbers may be added to the acids, and their bases in saline compounds; which figures, or their multiples, will represent all their combinations respectively. Thus, in sulphate of barytes a particle of sulphuric acid weighs 33, of barytes 67. Muriatic acid 18, of soda 24, &c. And these numbers may be conceived to represent the relative weights of an integrant "particle of each of these substances, compared with hydrogen as unit. From these data, Dr. Thompson was led to believe that the weight of an integrant particle of oxalic acid is 39,5, (p. 88.) and hence that it consists of 4 atoms of oxygen, 3 of carbon, and 2 of hydrogen; and that oxalic acid ought to contain 61 of oxygen, 34 carbon, and 5 of hydrogen, numbers which indeed approach sufficiently near to the former state

=

ments. With regard to the decomposition of oxalic acid by heat, let us suppose 3 particles of oxalic acid to be decomposed at once, and to resolve themselves into the 12 of oxygen+9 of carbon + 6 of hydrogen: the products will be 4 particles of carbonic acid 8 oxygen + 4 carbon, weighing 66; 2 of carbonated hydrogen = 2 carbon + 6,5 hydrogen, weighing 13; 2 of carbonic oxyd 2 of oxygen + 2 carbon, weighing 21; 2 of water 2 of oxygen + 2 of hydrogen, weighing 14; 1 of charcoal = 1 charcoal weighing 4,5 = 4,5. This sum of these respective materials coincides with the composition of 3 particles of oxalic acid, and their respective weight to hydrogen, namely 118, 5. If we refer these statements to 100 parts of acid, and join together the 2 gaseous products, the decomposed acid ought to afford 55,70 carbonic acid; 28, 69 carburetted hydrogen; 11,81 of water; and 3,80 of charcoal; and the results actually obtained by Dr. Thompson were carbonic acid 59,53; carburetted hydrogen 24, 28; water 11, 51; and charcoal 4,68. It is impossible to expect a more correct correspondence between the theory, and the quantities of the ingredients thus obtained by experiment. Dr. Thompson has extended his inquiries in a similar manner to the composition of sugar, and to the formation of oxalic acid and they are attended with equal success. But we can,

:

not enter farther into detail.

Altogether, we think this paper very valuable; and doubt not that Mr. Dalton will congratulate himself on having such a powerful convert to his theory. The simplification of which its application admits by using the initial letters of the several component parts, as h for hydrogen, c for carbon, &c. is much in its favour. Though the printer's adoption of the w, for the omega which was meant to designate oxygen, is droll enough. We will not anticipate what we hope soon to state more fully relative to Mr. Dalton's curious theories: but we may just remark here, that since it has been customary to refer specific gravities, specific heats, &c. to one substance, namely water, we think, notwithstanding its being a compound body, it may be found expedient to be retained for the standard of the relative weights of the atoms, or, as they will now be termed, the atomic gravities of bodies, rather than introduce a new substance, viz. hydrogen, as the comparative unit.

V. On Super-acid and Sub-acid Salts. By William Hyde Wollaston. M. D. Sec. R. S. Read Jan. 28. 1808.

In the paper on oxalic acid, Dr. Thompson has ingeniously shewn that the quantity of acid in the super-oxalates of potash and of strontia is just double the quantity which exists in the neutral oxalates. Dr. Wollaston, in the paper before us, shews that the same law prevails in other super-acid and

sub-acid salts, and that all similar facts are but particular instances of Dalton's general theory respecting the chemical elements of bodies; namely, that when two elements unite to form a third substance, one atom of one joins to one atom of the other singly; and if either be in excess, it takes place in a ratio of some simple multiple of the number of its atoms. The following facts are advanced by Dr. Wollaston in illustration of this important doctrine. The gas obtained by muriatic acid from 4 grains of carbonate of potash, which salt had been previously exposed to a red heat, was exactly equal in bulk to that quantity evolved from 2 grains of crystallized potash; hence the alkali after exposure to a red heat had parted with exactly half its quantity of gas. Saturated and sub-carbonate of soda yielded the same results. When 20 grains of carbonate of potash were heated with 25 grains of sulphuric acid to dryness, and lastly exposed to a red heat, the super-sulphate of potash produced was found to require very nearly 20 grains of carbonate of potash for saturation. Two separate and equal quantities of super-oxalate of pot. ash being taken, and one of them decomposed at a red heat, the remaining alkali exactly neutralized the excess of acid of the other portion. In like manner, nitric and muriatic acids can only take half the alkali from super-oxalate of potash; the salt which crystallises after solution in either of these acids, is a quadruple oxalate containing 4 times as much acid as would neutralise the residual alkali. The alkali of 30 grains of this salt must be obtained, by exposing it to heat, in order to neutralize the excess of acid in 10 of the same substance. The limit to the decomposition of super-oxalate of potash is like that to the decomposition of sulphate of potash by nitric acid, for nitric acid only withdraws one half of the potash, and the remainder of the salt is converted into a super-sulphate. To learn whether oxalic acid was capable of combining with potash in a proportion intermediate between the double and quadruple quantities of acid, Dr. Wollaston neutralized carbonate of potash by oxalic acid, and added a sufficient excess of acid, so that it might unite and crystallise in the ratio of 3 to 1; but the first crop of crystals obtained was the common binary oxalate, and the remainder, being properly selected, consisted of crystals of the quadruple oxalate. To account for this incapability of disposition of these bodies placed within the sphere of action to unite in the proportion of 3 to 1 by Dalton's theory, the neutral salts according to Dr. Wollaston, may be considered as 2 of potash + 1 of acid; the binary oxalates as = 1 potash + acid, or 2 of potash + 2 acid, and the quadroxalates as

1 potash + 2 of acid, or 2 potash + 4 of acid: but

as this explanation admits a double share of potash in the neutral salt, it is not satisfactory. Hence Dr. Wollaston is inclined to believe, that the arithmetical relation alone is insufficient to explain the mutual action of the elements of compound bodies; and he ingeniously remarks, that we may be obliged to acquire a geometrical conception of their relative arrangement in all the three dimensions of solid extension.' The most simple hypothesis suggested with regard to this subject is, to suppose that the limit to the approach of the particles is the same in all directions, and that their virtual extent. is spherical. In this case, when different kinds combine singly, there is but one mode of union. If the combination takes place in the ratio of 2 to 1, the arrangement is effected at opposite poles of that to which they unite. If they combine in the ratio of 3 to 1, they may be arranged symmetrically at the angles of an equilateral triangle in a great circle surrounding the single atom. If there are 4 particles to 1, a stable combination will take place, if the 4 particles are arranged at the angles of a regular tetrahedron. This geometrical arrangement of the primary elements of matter, Dr. Wollaston remarks, is altogether conjectural, and must not be confounded with the results of the facts stated before; these are sufficiently distinct and satisfactory, at least with regard to the existence of the law of simple multiples, though the nature of the geometrical arrangement may perhaps remain for ever unknown.

This paper furnishes additional evidence of the truth of an observation we made in our third volume (p. 1100), respecting the mutual relationship and dependence of several sciences. Some philosophers have endeavoured to sever chemistry from mathematics; but recent discoveries will render their attempt futile. Dalton and Smithson have the merit of correcting the processes of the chemists by the aid of arithmetical com putations; and Dr. W. now shews that geometry may not merely be useful in the developements of crystallography, as had been evinced by Hauy, but in explaining the phenomena of chemical combination. At such an era in the history of chemistry,we look with solicitude to the future labours of Dalton and Wollaston; as they are the only English philosophers, that we recollect, who are as well versed in mathematical as they are in chemical investigations.

VI. On the Inconvertibility of Bark into Alburnum. By T. A. Knight, Esq. F. R. S. Read Feb. 4, 1808.

In this paper, Mr. Knight endeavours to prove that bark, formed as we have described at p. 22 of the present volume, remains in the state of bark, and that no part of it is converted VOL. V. Kk

« PreviousContinue »