[AUG. length; the ends next the skin are almost always considerably finer, and the outer ends generally coarser, than the rest; but this difference is greater in some kinds of sheep than in others, and as far as I have observed, it is less in the Merinos and their crosses than in other sheep: there is also far less difference in the different parts of the same fleece in these breeds than in others; still however this difference is very observable, although it is probable that some part of the sheep might be found, which in all cases might fairly be considered as affording nearly the average of the whole fleece; and I imagine that the part of the back about the loins is the most likely to be possessed of this property; so that the middle of the fibres of this part of the fleece might be assumed, in the finer kinds of wool, as affording a fair measure for the whole. III. Scale of the Eriometer. The theory, which suggested to me the construction of the eriometer requires some corrections in its immediate application, which depend on circumstances not completely understood at present, therefore, I shall only employ, for the determination of the true value of the numbers of its scale, an experimental comparison of its indications with some microscopical measurements, which Dr. Wollaston has been so good as to perform for me, with an admirably accurate micrometer of his own invention. The dust or seed of the lycoperdon bovista he finds to be of an inch in diameter: this substance gives very distinctly 3.5 on the scale of the eriometer; and 3·5 × 8500 = 29750. The globules of the blood measured; and immediately afterwards, when examined in the same state by the eriometer, indicated about 64; and 6·5 × 4900 31850. A wire of platina, obtained by a very ingenious method, peculiar to Dr. Wollaston, measured; and when coiled up, gave n. 9 of the eriometer; and 9 × 3200 = 28800. The mean of a considerable number of comparative observations on fibres of wool, between n. 20 and 30, afforded also 28800 for a product. A mean of these experiments gives very nearly for the unit of the scale of the eriometer. Some former investigations had led me to attribute to this unit a value somewhat smaller, especially for the lowest numbers; and I had obtained a formula, and made a table, for ascertaining the true dimensions of any substance measured by the instrument, according to the result of these investigations; but since my later experiments seem to have superseded the mode of calculation which I had adopted, I think it unnecessary to insert the table. Having sufficiently ascertained the true value of the indications of the eriometrical scale, I shall now enumerate the mea Human blood diluted with water, 5; after standing some Vigonia wool.... .3 .31 .61 .61 .15/1 Siberian hare's wool, Scotch hare's wool, foreign coney wool, yellow rabbit's wool, about Mole's fur, about.. Skate's blood, very indistinct, about American rabbit's wool, British coney wool, about. Buffalo's wool ..... Saxon wool, a few fibres, 17, some 23, chiefly An Escurial ram, at Lord Somerville's show, 23 to Mr. Western's South Down, some specimens. Lioneza wool, 24 to 29, generally Paular wool, 24 to 29, generally Alpacca wool, about.. Farina of laurestinus .... Ryeland Merino wool, Mr. Henty Seed of lycopodium, beautifully distinct Coarse wool, from some worsted .20 It would not be difficult to obtain from these measures a tolerable approximation to the value of wool at its usual prices. If we square the number, and subtract 325, the remainder will be about the number of pounds that are worth 100 guineas. Thus, for good Lioneza, n. 25, 25 x 25 325 = 300, giving 7s, a pound; for moderate South Down, n. 35, 35 x 35 - 300 = 900, or 2s. 4d. a pound: which is probably about the proportional value, though both the proportional and the real values must fluctuate according to the demand of the manufacturer. (To be continued.) ARTICLE X. On Sir H. Davy's Theory of Chlorine, and its Compounds. By Mr. William Henderson, Member of the Royal Medical Society of Edinburgh. (Continued from p. 13.) II. Oxymuriatic Gas, by its Action on Metals and Inflammables, produces Substances differing essentially from the Oxydes of the same Bodies. The new theory was, until very lately, secure from assault on this quarter; for except two passages in the Philosophical Transactions, nothing definite had been advanced respecting this point by its supporters. These passages I insert : "Muriatic acid gas, as I have shown, and as is farther proved by the researches of MM. Gay-Lussac and Thenard, is a compound of a body unknown in a separate state, and water. The water, I believe, cannot be decompounded, unless a new combination is formed; thus, it is not changed by charcoal ignited in the gas by voltaic electricity; but it is decompounded by all the metals; and in these cases hydrogen is elicited, in a manner similar to that in which one metal is precipitated by another, the oxygen being found in the new compound."* "In some experiments, made very carefully by my brother, Mr. John Davy, on the decomposition of muriatic acid gas by heated tin and zinc, hydrogen equal to about half its volume was disengaged, and metallic muriates, the same as those produced by the combustion of tin and zinc in oxymuriatic gas, resulted." + These two authorities are in very positive terms; and if they are to be relied on, the products of the action of oxymuriatic gas on metals, though not similar to those which result from the action of oxygen on the same hodies, are precisely what they were thought to be, viz. compounds of the metals and oxygen, with which the muriatic acid, condensed from the want of Phil. Trans. 1810, p. 67. + Phil. Trans. 1810, p. 237. water, has united to form muriates. To this conclusion it will of course be objected, that these passages were written previous to the adoption of the new theory. This objection will, however, vanish, on considering, that it is not to the opinions, but to the facts contained in the passages cited, that my reasoning has reference. By the publication of Mr. J. Davy's paper on the combinations of chlorine with the metals, * I am enabled to bring this part of the discussion more completely under examination thau could before be done; and in doing this I shall be as brief as the nature of the reasoning employed will allow. 66 The first compound noticed in this paper is cuprane; which is formed by exposing slips of copper, partially immersed in muriatic acid, to the atmosphere.' Mr. J. Davy says that in this process the deliquescent muriate is formed-" which flowing into the muriatic acid is changed by the action of the immersed copper into cuprane." According to this view, cuprane can not contain more, but may have less chlorine than can be yielded by the muriatic acid of the deliquescent muriate; yet the analysis given ascribes to it a pr. portion of chlorine exceeding by 12 18 per cent. what it can contain consistently with Chenevix's analysis of the proto-muriate, and approaching within a minute quantity to the proportion given by Proust, † as belonging to the per-muriate. Again, cuprane is stated to be composed of 64' of copper, and 36 of chlorine. According to Chenevix, the proto-muriate contains 70.25 of protoxyde (of which 63 161 is copper), and 24.75 of muriatic acid. Now it is worthy of notice, that, on the principles of the old theory, the quantity of oxygen contained in the protoxyde, is capable of forming oxymuriatic gas with 24:383 of muriatic acid; so that the only difficulty in reconciling these analyses is the water contained in the protomuriate, which Mr. J. Davy seems to have laid to the account of the chlorine. From the analysis of cupranea having been performed on its solution, it appears that Mr. J. Davy in fact examined the deliquescent muriate, into which, he says, that it is converted by the action of water. But the result of Mr. J. Davy's analysis exceeds in the proportion of the chlorine that given by Proust by 26 816 per cent. How can this quantity of chlorine escape from its combination when the compound is dissolved in water, and again enter into union with the copper on the water being separated. Another difficulty also lies against the analysis of cupranea. Mr. J. Davy says that it is composed of 47 of copper and 53 of chlorine. Now 47 of copper, in passing to * Phil. Trans. 1812, p. 169. + Ann, de Chim. tome xxxii. 47. 1 the state of peroxyde, unite with 15-67 of oxygen; which quantity of oxygen, on the principles of the old theory, can convert 53.93 of muriatic acid into oxymuriatic gas; or (which is the same thing), on the basis of the new theory, can unite with the hydrogen contained in that quantity of muriatic acid gas. But it appears by Proust's analysis, that 62.67 of peroxyde of copper cannot combine with, or act on more than 37.8 of muriatic acid. A deficiency of previous analyses, in which I could confide, prevented my examining in detail Mr. J. Davy's account of the compounds of chlorine with tin, iron, manganese, zinc, arsenic, antimony, and bismuth. I may, however, be permitted to say a few words respecting the compounds of iron. It is stated by Mr. J. Davy, that ferranea has more chlorine than ferrane, and that the solutions of these compounds are the red and green muriates of iron respectively. Sir H. Davy states, that a solution of the red muriate may be converted into the green by sulphureted hydrogen. This is easily explained, if we suppose, according to the old theory, that the iron is converted into a protoxide by the sulphureted hydrogen: but if we suppose the iron to be in both cases in the metallic state, or, in other words, exposed to a substance, with which it cannot unite until it has assumed that state, the effect of the sulphureted hydrogen seems by no means easily explained. Horn-lead is said by Mr. J. Davy to contain 74.22 of lead, and 25.78 of chlorine. According to Kirwan's analysis, it has 76 of lead, and 18.23 of muriatic acid; which, by the new theory, can yield only 17.6 of chlorine. In this case, the proportion of lead seems to answer very well; but that of chlorine is over-rated, by 8.18 per cent. Again, by the analysis of Kirwan, horn-lead contains 5.77 of oxygen; which, on the principles of the old theory, are sufficient to form 25-64 of oxymuriatic gas, by union with muriatic acid. Is this very singular coincidence, with the others before stated, to be regarded as merely accidental? III. When carefully dried, Oxymuriatic Gas is incapable of acting on Charcoal. This seems accounted for, on the old theory, by saying, that the oxymuriatic gas, if it acted on the charcoal, and imparted its oxygen to it, must give rise to a quantity of muriatic acid; but that this acid being incapable of existing in an insulated state, and there being no water present, those actions by which its evolutions would be caused are prevented. In this way, the whole comes to be merely an additional instance of the power of *Researches, &c. p. 182. + Thomson's System, &c. iii. p. 265. |