40 MEMOIR OF DR. DALTON, AND 



to the given temperature 180°. Then -—j- = lo^iy = 2 

 for the space; or the air becomes of twice the bulk." 

 p. 572. " In short, in all cases the vapour arises to a 

 certain force according to temperature, and the air adjusts 

 the equilibrium by expanding and contracting as may be 

 required." 



" The notion of a chemical affinity subsisting between the 

 gases and vapours of different kinds cannot at all be reconciled 

 to these phenomena." p. 574. 



This notion of chemical affinity holding the gases in 

 solution had begun to die out. 



In essay third, " On evaporation" he concludes that the 

 quantity of any liquid evaporated in the open air is directly 

 as the force of steam from such liquid at its temperature, all 

 other circumstances being the same. He adds a *' table 

 shewing the force of vapour, and the full evaporating force 

 of every degree of temperature from 20° to 85°, expressed in 

 grains of water that would be raised per minute from a 

 vessel of six inches in diameter, supposing there were no 

 vapour already in the atmosphere." p. 585. He obtained the 

 evaporation from a surface when the air was still and when 

 in motion. He adds also rules to find the amount of water 

 that can be evaporated from a given surface when the 

 temperature of the air is given, and the condensing point, 

 and to find the force of the aqueous vapour. 



The fourth essay on the expansion of elastic fluids by heat 

 proves the law already stated. 



The position of the question when he took up the subject 

 may best be explained by himself, he says, p. 595, " The 

 principal occasion of this essay is another on the same subject 

 by Messrs. de Morveau and du Vernois, in the first vol. of 

 the Annalesde Chimie. It appearing to them that the results 

 of the experiments of De Luc, Col. Roy, de Saussure, 

 Priestley, Vandermonde, Berthollet, and Monge, did not 

 sufficiently accord with each other ; and that it would be of 



