332 Mr Graham on the absorption of Vapours hy Liquids. 



acid is ever capable of increasing in weight when exposed to 

 the air, as sulphuric and nitric acids are known to do, and as 

 occurred in the case of the stronger muriatic acid in the fore- 

 going experiment. But I have frequently observed muriatic 

 acid, of all degrees of strength, intermediate between 1.190 

 and 1.100, to increase in weight by the absorption of hygro- 

 metric moisture, when the weather was damp, and the tem- 

 perature not above 65P. When the acid is strong it emits mu- 

 riatic acid gas at the same time that it absorbs aqueous vapour, 

 till it becomes of specific gravity 1.0960. But when acid, di- 

 luted to any degree below that strength, is exposed in a dry 

 atmosphere, no material quantity of the acid gas is emitted, 

 but the acid concentrates by the emission of aqueous vapour, 

 till its specific weight rises to 1 .0960. The boiling point of 

 muriatic acid is at a maximum when of that strength, as was 

 observed by Mr Dalton ; and it consists of exactly one atom 

 acid and sixteen atoms water, as Dr Thomson remarked. 



As evidence of the power of muriatic acid to absorb moisture 

 from an atmosphere not particularly dry, and to increase in 

 weight, I may be allowed to state one experiment, made lately 

 in the month of January. Three small porcelain basins, each 

 containing 200 grains of liquid, were exposed together, with 

 paper covers, in a room in which there was no fire. The liquid 

 in No. 1 was muriatic acid of specific gravity 1.185. In No. 

 2 the same, diluted with half its weight of water. In No. 3 

 pure water. It had been previously ascertained that the mu- 

 riatic acid contained no sulphuric acid. The basins were 

 weighed every twenty-four hours, and the following results 

 obtained : — 



Weight in Grains. 



