1826.] Scientijic Notices — Chemislry^^ 73 



retained by a liquid, because the absorbed gas is itself then in 

 a liquid state ; and the volatility of all liquids, whether by 

 themselves or mixed with others, is dependent upon pressure 

 and temperature. The law, however, which Dr. Henry deduced 

 from his experiments upon carbonic acid, viz. that the quantity 

 of a gas which water absorbs is directly proportional to the 

 pressure, is at variance with this theory. It is not likely that 

 Dr. Henry would have come to the same conclusion, had he 

 experimented upon the more absorbable gases. In the case of 

 muriatic acid gas, for instance, it is unlikely that he would have 

 succeeded in impregnating water with a double portion by 

 doubling the pressure. There may, nevertheless, be an ap- 

 proximation to such a law, when the quantity of gas absorbed 

 IS inconsiderable, as it is in the case of carbonic acid gas ; our 

 knowledge of the laws by which a volatile is retained by a more 

 fixed liquid, bein^ too superficial to enable us at present to 

 decide the point in question. The existence, however, of a 

 general mechanical law of that description is incompatible with 

 any chemical theory which can be given. Supposing such a 

 law to hold, it is remarked by Dr. Thomson, that ** the pro- 

 portion of the ingredients in this case is entirely regulated by 

 the bulk, whereas, in chemical combinations it is regulated by 

 the weight." Dr. Thomson, notwithstanding this admission, 

 attempts ingeniously to reconcile such a law to his modification 

 of the chemical theory.* 



The same objections are applicable to the analogous mecha- 

 nical law, that the quantity of a gas absorbed, estimated by the 

 bulk, is unaft'ected by variations in temperature. Such a law 

 would be agreeable to the theory illustrated, if it were true that 

 the pressure of vapours from liquids is exactly proportional to 

 the temperature. But we know that the elasticity of vapours, 

 over their liquids, increases in a much higher ratio than the 

 temperature. Hence we are led to propose a different law, viz. 

 that by increasing the temperature of a liquid, we diminish its 

 capacity to absorb any gas, not in the same but in a much 

 greater proportion. 



Dr. Henry and Mr. Dalton have proved, that the amount of 

 any gas, absorbed by a quantity of water in a vessel, depends 

 greatly upon the gaseous residue. This fact is deducible from 

 the supposition, that the gases are liquefied when absorbed. 

 For all liquids continue to evaporate until they are pressed 

 upon by an atmosphere of their own vapour, equal in elasticity 

 to that which they are capable of evolving at the temperature 

 of the experiment. In a solution of carbonic acid in water, we 

 ought, therefore, to expect carbonic acid to be given out or 

 to evaporate, till an atmosphere of that gas be formed of elas- 



* System of Chem. vol. ii. p. 61» 



