302 Dr, Thomson on the Lifluence of Humidity [April 



extraneous bodies, and supply the deficiency with copper, 100 

 parts will consist of 



Sulphur 35-16 



Iron 32-20 



Copper 32-64 



100-00 



Still leaving the copper about two per cent, too little, and the 

 sulphur and iron in excess. If, however, we adopt the same 

 plan with the analysis of the mamellated yellow copper, we shall 

 have a very near approximation to the theoretical composition 

 which I have suggested ; viz. 



Sulphur 34-46 



Iron 30-80 



Copper 34-74 



100-00 



Artjcjue VII. 



On the Injiuence of Humidity in modifying the Specific Gravity 

 of Gases. By Thomas Thomson, MD. IRS. Regius Professor 

 of Chemistry in the University of Glasgow. 



A FRIEND of mine, whose inteUigence and candour I estimate 

 very highly, mentioned to me some time ago that he considered 

 the specific gravity of hydrogen gas given in my paper pubhshed 

 in the Annals of Philosophy, vol. xvi. p. 168, as inaccurate; 

 because the gas had not been previously freed from moisture ; 

 and being collected over water, must have contained as much 

 vapour as was compatible with the temperature at which the 

 specific gravity was taken. This objection renders it proper for 

 me to enter somewhat more into detail than I did in that paper, 

 in order to show how far my mode of experimenting guarded 

 against this obvious source of inaccuracy. I do this the more 

 wiUingly, because it will give me an opportunity of calling the 

 attention of chemists to a property of vapour, ascertained indeed 

 more than ten years ago ; but which does not seem to have yet 

 attracted the attention of scientific men ; at least I am not 

 aware of any allusion to it in any of the systematic works on 

 heat, which have lately appeared. 



In the second volume of the second series of the Manchester 

 Memoirs, published in 1813, there is a paper by John Sharpe, 

 Esq. entitled '' An Account of some Experiments to ascertain 

 whether the Force of Steam be in Proportion to the generating 

 Heat." In this paper, Mr. Sharpe relates experiments proving 

 the truth of the two following propositions : 1 . Water heats 

 equably, or in the same time (supposing the heating cause the 



