stances under which it is generally formed, the hydride of zinc is decomposed as fast as it is created. 1st Stage.-HI+ Zn Zn = Zn H + Zn I. 2nd Stage.-Zn H+HI=HH + Zn I. 210. The student must, however, observe, that the formation of molecular atoms of the alcohol radicals was not proved by the simultaneous liberation of two atoms of ethyl by the action of iodide of ethyl on zinc-ethyl, and the analysis of the substance could not aid in the proof. But Brodie at once suggested a mode of proving the existence of these molecular atoms by analogy. He said the next step in these experiments should be the decomposition of iodide of methyl (C, H, I), or iodide of amyl (C1o H1, I), by zinc-ethyl; in which case, he said, the formation of a compound hydro-carbon might be anticipated of the formula C, H, C, H, (ethyl-methyl), or C1o H, CH, (ethyl-amyl).* Since that time Wurtz has actually obtained a series of these double radicals by decomposing, by means of sodium, equivalent proportions of the iodides. Thus, in the preparation of ethyl-amyl the following reaction occurs : C, H, I+C1o HI+Na Na= C10 H11, C, H, +2 Na I. 10 211. The formation of these heterogeneous radicals affords very strong analogical proof of the existence of • molecular atoms of the homogeneous radicals. This is confirmed by the boiling-points and vapour-densities of these bodies. The boiling.point of the heterogeneous radicals rises gradually as the number of equivalents of carbon and hydrogen increases; and this regular progression takes place in the homogeneous radicals if they are represented by the double atom; the vapour-densities as well as the boiling-points of the homogeneous radicals are what would be theoretically assigned to them, if we represented them by the double atom. These proofs show that the homogeneous and heterogeneous radicals are both constructed upon the same molecular plan, and that Brodie's view of their constitution is the correct one. We refer the student to the original memoir by Brodie, "Observations on the Constitution of the Alcohol Radicals, and on the Formation of Ethyl," in the Journal of the London Chemical Society, vol. iii. Tetryl-amyl C1, H20=C, H,, C10 H11 0.7011 3.053 2.972 62 26 0.7069 3-522 3.455 ... 3.426 3.455 881 0.7057 4.070 3.939 0-7247 4:465 4.423 ide of amyl) C., H22=C10 H11, C1o H11 0-7413 4.899 4-907 Tetryl hexyl C20 H22=C, H,, C12 H13 Hexyl (Hexylide 82 18 10626 13226 158 4.917 4.907 155 44 of hexyl) C., H26=C1, H13, C1, H1, 0.7574 5-983 5-874 202 26 212. "It may further be remarked, in illustration of the pre-existence of the original molecular arrangement of the component groups of these compound bodies, that Wurtz finds that amyl preserves its rotatory action on a ray of polarized light when it passes into these compounds, ethyl-amyl displaying the power of rotating a polarized ray to the right; whilst amyline, valeric acid, and other derivatives of amylic-alcohol, in which there is _reason. to suppose that the molecule of amyl is destroyed, exert no rotatory power." *Methylide of methyl and ethylide of ethyl are both gases at the ordinary temperature, they are not liquefied by a cold of 0° F. +Tetryl, butryl or valyl. Hexyl or caproyl. 123 CHAPTER IV. NUMERICAL RELATIONS OF EQUIVALENT NUMBERS.BINARY THEORY OF SALTS. Numerical relations of equivalent numbers, 213. The views of Prout, Thomson, and Dumas, on the atomic weights of bodies, 213. The views of Berzelius and Stas on the atomic weights of bodies, 218. Binary theory of salts, 219. Facts which appear to support the binary view, 221. Both views of the constitution of salts hypothetical, 227. Objections to the binary theory, 227. Exercises, 229. 213. Numerical relation of equivalent numbers.—As the atomic weights of carbon, oxygen, sulphur, bromine, and many of the other elements, are exact multiples of that of hydrogen, Prout and Thomson considered that it was a law of nature that the atomic weights of all the other elements are divisible by that of hydrogen. If this were the case, it might be supposed that hydrogen was the only elementary body, and that the larger and heavier atoms of the other so-called elementary bodies are produced by a combination of the requisite number of atoms of hydrogen, and that these different combinations of the hydrogen atoms are the cause of the difference in properties exhibited by the different bodies. Dumas has devoted great attention to this subject, and he concludes, from the results of his investigations, that, in a modified sense, Prout's law is true; and he considers that the elementary bodies, the atomic weights of which he regards as accurately known, may be arranged in three groups, viz.: 1. Bodies which are represented by multiples of a whole number of hydrogen. 2. Multiples by the number 05 of that of hydrogen. 3. Multiples by 0-25 of that of hydrogen. 1. Bodies which are multiples by a whole number of the equivalent of hydrogen: 2. Multiples by 0.5 of the equivalent of hydrogen : 3. Multiples by 0.25 of the equivalent of hydrogen : 214. The relations exhibited between the members of many of these bodies which are chemically allied, are often very remarkable. 1. Thus it has been observed that, in several instances where two elements are in close chemical relation to each other, they have atomic weights which are identical, and in others they are nearly identical, as in the following examples : 215. The following have nearly equal atomic weights:Chromium, 26.7; manganese, 27.5; iron, 28. Copper, 31.75, and zinc, 32-75. and osmium, 99.6. Platinum, 987; iridium, 987; 2. In other cases, the ratio of the atomic weights is as 1 to 2; for instance: = 8 Oxygen Sulphur = 16 3. We are enabled to arrange the various substances reputed elementary, by certain resemblances, into various well-marked groups; and those composing the same group are capable of substituting one another in compounds, without altering the general character of the body. Such a group is the triad-chlorine, bromine, iodine. Now, all the essential qualities of bromine are intermediate between those of chlorine and iodine, and so is its atomic weight. Thus, could we by any means take half an atom of chlorine, and add to it half an atom of iodine, we might expect to produce bromine. Similar triads are found in sulphur, selenium, and tellurium; lithium, sodium, and potassium; and calcium, strontium, and barium. It is a curious and interesting fact that several members of any one of these triads are generally found together. 216. Despretz has attempted to ascertain whether certain of the so-called elements are decomposable; and he concluded from his researches that they are incapable of decomposition. Dumas, in reply to Despretz, prefaced his remarks by presenting the following table, which exhibits an interesting relation between the equivalents of certain simple and compound bodies : Fl 19, Cl 35.5, Br 80, I 127 N 14, P 31, As 75, Sb 122 : Difference, 5. Mg 12-25, Ca 20, Sr 43.75, Ba 68-5, Pb 103.5 Diff. 4. S 16, Se 39.75, Te 645, Os 99.5) 08, Ammonium 18, Methylamine 32, Ethylamine 46, Methylium 15, Ethylium 29, Propylium 43, Butylíum, 57, &c. Diff. 3. 217. Since the radicals (elements) in mineral chemistry present the same general relations as those in organic, Dumas believes there is reason for bringing the two branches more closely together than is usually done. We can decompose the latter, and there is no proof that we may not decompose the former. He thus sums up his conclusions:-(1.) The compounds which the three king |