IQ ON MIXED GASES. 



Examination of tin^s* discountenances the idea of the compound being a me- 

 Mr. Dalton's chanical mixture of any description -whatever; for when a 

 cd gSes ^ ' ^^^^'''^ber of diaphanous bodies of different speciiic gravities are 

 mixed together, they form an aggregate which is opaque ; 

 but the union of the substances by fusion renders the mass 

 transparent in many instances. Now as the atmosphere is 

 diaphanous, we are obliged, by the principles of sound argu- 

 ment, to consider it in the light of a compound, the ingrediefit« 

 of which are united by a chemical tie.— Whatever may be the 

 condition of the elastic fluids which enter into the composition 

 ot common air, one thing is certain from a preceding para- 

 graph of this Essay ; namely, noon^ofthem can maintain a 

 separate equilibrium as long as it makes an individual of the 

 aggregate ; consequently, each particle of the compound must 

 fee urged by a force resulting from the general action of the 

 mass, not by a pressure occasioned by a particular member 

 ©fit. 



On this account, it is iinpossible for the acqueous part of 

 e-ommon air to preserve the character of a gas at low tempe- 

 ratures ; because steam cannot support 30 inches of mercury 

 unless it is heated to 212 degrees of Farenheit's thermometer; 

 were it then practicable to mix vapour of a less heat with at- 

 n:iospherical air, the spring of the gases would reduce it in an 

 instant to the state of a liquid; so that the difficulty, which 

 renders De Luc's theory objectionable in its original form, is 

 Kot removed in reality by the present modification of it. 



The theory of mixed gases has been found to be indefen- 

 sible on the principles of the mechanical philosophy ; and I 

 s>uspcct that part ol it which relates to the separate existence of 

 vapour in the atmosphere, will prove equally unfortunate 

 when brought to the test of experiment. Mr. Dalton, in all 

 probability, supposed he had done all that the confirmation of 

 this theory required, by inventing the doctrine of separate 

 equilibria, for nothing more has been offered in support of his 

 opinions, particularly of that relating to the existence of un- 

 combined vapour pervading the atmosphere, unless the state- 

 ment of the following experiment, with his explanation of it, 

 may be referred to this head. If two parcels of dry air, which 

 are equal in bulk, density and temperature, be confined by 

 equal columns of mercury, in two tubes of equal bores, one of 

 which is wet and the oth^ di y ; the air, which is thus ex- 



