¥815.] Gaseous Bodies and the Weight of their Aioms. 328 
Biot and Arrago, is 1:278. Now if we suppose this sp. gr. to be 
erroneous in the same proportion that we found the sp. gr. of 
oxygen and azote to be above, (which, though not rigidly accurate, 
may yet be fairly done, since the experiments were conducted in a 
similar manner), the sp. gr. of this gas will come out about 1°2845 ;* 
and since it is a compound of one volume chlorine and one volume 
hydrogen, the specific gravity of chlorine will be found by calcula- 
tion to be 2°5.¢ Dr. Thomson states, that he has found 2°483 to 
be near the truth, t and Gay-Lussac almost coincides with him. § 
Hence there is every reason for concluding that the sp. gr. of chlo- 
rine does not differ much from 2°5. On this supposition, the sp. 
gr. of chlorine will be found exactly 36 times that of hydrogen. 
On the Specific Gravities of Elementary Substances in a Gaseous 
State that do not at ordinary Temperatures exist in that State. 
1. Iodine.—I had some reason to suspect that M. Gay-Lussac had 
in his excellent memoir rated the weight of an atom of this sub- 
stance somewhat too high; and in order to prove this 50 grains of 
iodine, which had been distilled from lime, were digested with 30 grs, 
of very pure lamellated zine. The solution formed was transparent. 
and colourless ; and it was found that 12-9 grains of zine had been 
dissolved. 100 parts of iodine, therefore, according to this experi- 
ment, will combine with 25°8 parts of zinc, and the weight of an 
atom of iodine will be 155,|] zine being supposed to be 40. From 
these data, the sp. gr. of iodine in a state of gas will be found by 
calculation to be 8°61 1111, or exactly 124 times that of hydrogen.** 
2. Carlon.—l assume the weight of an atom of carbon at 7°*5. 
Hence the sp. gr. of a volume of «it in a state of gas will be found 
by calculation to be 4166, or exactly 12:times that of hydrogen, 
3. Sulphur.—The weight of an atom of sulphur is 20. Hence the 
specific gravity ofits gas is the same as that of oxygen, or I*1111, 
and consequently just 16 times that of hydrogen. 
* As W104; TLIPI1 s: 1278 + 1-286. 
Avd as ‘969 ; -9722 :; 1°278 ; 1283, The mean of these is 1:2845, 
+ Let « = sp. gr. of chlorine, 
Then a = 1/2845, 
And x = 2°569 — ‘0694 = 2°5 very nearly, 
t Annals of Philosophy, vol. iv, p. 13. 
§ Ditto, vol. vi. p. 126. , 
|} As 25°8 ; 100 :: 40: 155. According to experiment 8th, stated below, 
the weight of an atom ef zinc is 40. Dr. Thomson makes it 40°9, which differs 
Very little. See Annals of Philosophu, vol. iv, p, 94. 
** One yolume of bydrogen combines with only half a volume of oxygen, 
bat with a whole volume of gaseous iodine, according to M. Gay-Lussac. The ratio 
in volume, therefore, between oxygen and iodine is as $ to 1, and the ratio in 
Weight is as 1 to 15°5. Now °5555, the density of fialf a volume of oxygen, multi- 
plied by 15:5, gives SGIIL1, and S6LI11 = -06944 = 124. Or generally, to 
find the sp. gr. of any substance in a state of gas, we have ovly to multiply half 
the sp. gr. of oxygen by the weight of the atom of the substances with respect te 
oxygen, See Annals of Philosophy, vol. y. p. 105, ’ 
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