<Jg \ METHOD OF ESTIMATING CHANCES IN GASES. 



V. 



Account of a fimple Method of ejiimating the Changes of Volume 

 produced in Gafes, by Alterations of Temperature, and of 

 Atmojpheric Prejfure, in the courfe of Chemical Experiments. 

 By Mr. H. Davy. Prof e (for of Chemijlry at the Rcyal 

 Jnjlitution. From their Journal. 



Elaftk fluids af- IT often happens that changes of atmofpherical preflure, 

 fur/an/tempc- anc * °^ tem P er ature, take place in the courfe of experiments 

 rature. on elaftic fluids ; and a knowledge of the alterations they pro- 



duce in their volume, is eflential to the preciiion and accuracy 

 of the refults. 

 Quantitie$ of In cafes when chemical clvanges are produced, it is impof- 



gafes muft be f 1D ] e j g a j n this knowledge by direct obfervation : and, in 

 eftmiated at fome _ , . & . . . 6 , J r r . , ' ' 



ilandard. coniidenng quanties, it is always uleful to eftimate the vo- 



lumes of gafes at fome ftandard, fixed upon in meafures of 

 the barometer * and thermometer. 

 Law for preflure. It is demonflrated by very accurate experiments, that the 

 Volume, in- volumes of elaftic fluids are inverfely as the weights com- 

 fure. prefling them. And, confequently, the changes produced 



upon gafes, by known changes in the atmofpherical prefliire, 

 may be ascertained in a very eafy manner. With regard to 

 the effects of temperature, however, it is much more difficult 

 to form a juft eftimalion by means of general laws. For 

 though the excellent experiments of Mr. Dalton f, and thofe 



of 



* Lavoifier's Elements, p. 406, 2nd Edit. 



f Manchefter Memoirs, Vol. V. p. §99. Mr. Dalton fays, " I 

 have repeatedly found that 1000 parts of common air, of the tem- 

 perature of 55 p and common preffure, expand to 1321 parts in the 

 manometer} to which adding 4 parts for the correfponding expan- 

 fion of glafs, we have 325 parts increafe upon 1000 from 55* to 

 212° j or for 157° of the thermometiic fcale. As for the expan- 

 iion in the intermediate degrees, which Col. Roi's experiments mow 

 to be a /lowly diminijbing one above the temperature of 57°, but 

 which de Morveaifs, on the contrary, mow to be a rapidly in- 

 creafmg one in the higher part of the fcale j I am obliged to allow 

 that Col. Roi is right, though it makes, in fome degree, againft an 

 hypothefis I have formed relative to the fubjeclj he has certainly, 

 however, made the diminution too great from 72° downwards, 



owing 



