64 EIGHTH REPORT — 1838. 



nitrate of silver, immediately tliey were cast, from the mould, and 

 wrapped one of them in paper, in the usual way -that this substance is 

 found in tlie sliops ; the other cylinder was transferred to a glass tube, 

 and sealed up hermetically, by means of the blow-pipe, without being 

 suffered to come in contact with organic bodies: it was pushed from 

 tlie mould into the tube by means of a glass rod. After a lapse of 

 three days, the paper was removed from the first, and it was then 

 sealed up in a tube, in a similar manner to the other. The two tubes 

 were now exposed to the direct rays of the sun, and in half an hour the 

 nitrateof silver that had lain in contact with paper was blackened, while 

 that in the other tube was not altered by six weeks constant exposure. 

 The whole amount of blackening of the cylinder that had been papered 

 was produced in the lialf hour. Nitrate of silver, free from oi'ganized 

 matter, is sometimes blackened by exposure to the air; but this may be 

 owing to the presence perhaps of sulphuretted hydrogen, accidentally 

 present. Atmospheric air too is, perhaps, seldom free fi'om organic 

 matter. 



On the Specific Gravities of Nitrogen, Oxygen, Hydrogen, and Chlo' 

 rine ; and also of the Vapours of Carbon, Sulphur, Arsetiic, and 

 Phosphorns. By the Rev. T. Exley, M.A. 



The author of this communication first shows the bearing of his new 

 theory of physics on questions relating to the combination of atoms, 

 which he classes according to their supposed absolute forces and rela- 

 tive spheres of repulsion. Among the consequences of this theory the 

 author mentions the deduction, that " equal volumes contain equal 

 numbers of atoms," and proceeds to show the application of this to the 

 construction of a general table of specific gravities for chemical com- 

 pounds in the gaseous form. Taking the specific gravity of air as 

 unity, he shows, from comparison of the best experimental results, that 

 the following specific gravities may be depended on within minute 

 errors : — • 



Carbon* . . . 10-12ths. 



Sulphur t . . . 60-9ths. 



Arsenic J . . . 10^. 



Phosphorus § . . 4^. 



Now these numbers, being compared with the atomic weights of the 

 substances, lead to the following simple rule for determining specific 

 gravities in all gaseous bodies : — Multiply the sum of the atomic 

 Aveights of the atoms of a single group by -^-^^ (the specific gravity of 

 hydrogen), the product is the specific gravity required. By this rule 

 the following table was calculated : — 



* The number for carbon is inferred from its gaseous combinations. 



t It is by calculation only 1°, but the author explains this difference by supposing 

 the sulphur vapour to exist in single groups of three atoms each, a)id gives reasons 

 for thinking this probable. 



X By calculation 5^- ; supposed to consist of single gi'oups of hpo atoms each. 



§ By calculation 2| ; supposccl to consist of single groups of two atoms each. 



