bones, as the bone must become soft before it swells; which softness is owing to defect of the secretion of phosphorated calcareous earth. The swelling of the bone compresses a part of the brain, called the spinal marrow, within the cavity of the back-bones; and in consequence the lower limbs become paralytic, attended sometimes with difficulty of emptying the bladder and rectum. M. M. Issues put on each side of the prominent bone are of great effect, I suppose, by their stimulus; which excites into action more of the sensorial powers of irritation and sensation, and thus gives greater activity to the vascular system in their vicinity. The methods recommended in distortion of the spine are also to be attended to. [To be continued.] V. On Oxalic Acid. By THOMAS THOMSON, M. D. F.R.S. Ed. Communicated by CHARLES HATCHETT, Esq., F.R.S. [Concluded from vol. xxxi. p. 253.] IV. Composition of Oxalic Acid. THE knowledge of the relative weights of the elements which compose oxalic acid, though of importance, is not sufficient to convey a clear idea of this compound, and in what respect it differs from tartaric acid, alcohol, sugar, and various other bodies possessing very different properties, though composed of the very same elements in different proportions. It has been ascertained, by numerous and decisive experiments, that elementary bodies always enter into combinations in determinate proportions, which may be represented by numbers. For example, the numbers which correspond to the four elements, oxygen, azote, carbon, and hydrogen, are the following: Oxygen C 4 6 5 4.5 Now, Now, in all compounds consisting of these ingredients, the proportion of the different constituents may always be represented by these numbers, or by multiples of them; thus, the composition of the following substances may be thus stated: 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 six, an atom of hydrogen one, &c. Water is composed of one atom of oxygen, and one atom of hydrogen; carbonic acid of two atoms of oxygen, and one of carbon, &c. This curious theory, which promises to throw an unexpected light on the obscurest parts of chemistry, belongs to Mr. Dalton. I have elsewhere illustrated it at considerable length*. The same law holds with respect to the salts. The acid and bases always combine in determinate proportions. We may affix numbers to all the acids and bases, which numbers, or their multiples, will represent all the combinations into which these bodies enter. Some of these numbers are given in the following table : * See System of Chemistry, iii. 424, &c. 3d edition. These These numbers may be conceived to represent the relative weights of an integrant particle of each of these substances; formed on the supposition that an atom of hydrogen weighs 1. It follows equally from this law, that the acids and bases combine particle with particle, or a certain determinate number of particles of the one with a particle of the other. One of the most important points in the investigation of compound bodies, is to ascertain the number which denotes the weight of an integrant particle of each of them, that of an atom of hydrogen being 1; because this number, or a multiple of it, represents the weight of each, which enters into all combinations; and because it enables us to estimate the number of elementary atoms of which each is composed. From a careful comparison of the table of oxalates, given in a preceding part of this paper, with the weight of the different bases already determined, it appears that the weight of an integrant particle of oxalic acid must be represented by the number 39.5. Now, what number of atoms of oxygen, carbon, and hydrogen, go to constitute an integrant particle of oxalic acid? We have assigned the relative weights of each of these atoms, and we have ascertained the relative proportions of the respective elements of oxalic acid. From these data it is easy to solve the problem. An integrant particle of oxalic acid consists of nine atoms combined together, namely, four atoms of oxygen, three of carbon, and two of hydrogen. 4 atoms of oxygen weigh 4 x 6 = 24 which together make up the weight of an integrant particle of oxalic acid. According to these proportions, 100 parts of oxalic acid is composed of For these weights, and the method of determining them, I refer the reader to my System of Chemistry, 3d edition, iii. 619. The numbers which I have there assigned are, I am persuaded, rather too low. numbers which do not indeed exactly correspond with the result of the preceding analysis, but which approach sufficiently near it to give the reasoning employed considerable probability at least, if it does not lead to certainty. We may now examine the decomposition which takes place when oxalate of lime is exposed to heat. Let an atom of oxygen be w, an atom of carbon c, and an atom of hydrogen h. An integrant particle of oxalic acid may be represented by 4 w + 3c + 2 h. We may represent the composition and weight of an integrant particle of each of the substances into which oxalic acid is decomposed by heat, by the following symbols and numbers: We may now conceive three particles of oxalic acid to be decomposed at once, and to resolve themselves into these substances, in the following proportions: We see that such a decomposition is possible. It remains only therefore to see whether the weights of these substances, which result from this hypothesis, correspond with the preceding analysis. Now, 4 particles 4 particles of carbonic acid weigh 4 × 165 = 66 2 X 10.5 = 21 Reducing these proportions to 100 parts of acid, and joining together the two inflammable gases, the numbers come out as follows: 55.70 we actually obtained 59.53 Carbonic acid Inflammable air 28.69 24.28 11.51 4.68 100.00 It is impossible to expect exact correspondence between the theory and hypothesis, till the numbers representing the weights of the elementary atoms be ascertained with more rigid accuracy than has hitherto been done. I satisfied myself with taking the nearest round numbers, which are sufficient at least to show an evident approximation to the proportions obtained by experiment. V. Composition of Sugar, and Formation of Oxalic Acid. When a compound body is decomposed, and resolved into a number of new substances, the products are almost always simpler, or consist of integrant particles, composed of fewer atoms than the integrant particles of the original body. Thus, though oxalic acid is composed of nine atoms, none of the products evolved, when that acid is decomposed by heat, Hence it is probable that sugar is a more compound body than oxalic acid, because nitric acid resolves it into a variety of new compounds, one of which is oxalic acid. It may be worth while to examine the action of nitric acid on sugar, and the formation of oxalic acid, more closely than has hitherto been done, as the investigation will furnish some data for estimating the composition of sugar. contain more than three atoms. Two |