18 HISTORICAL INTRODUCTION. 



IV. For the next step in the progress of the 



sac's theory , , , .~ T 



of volumes, atomic theory, we are indebted to Gay-Lussac. 

 In the second volume of the Memoires D'Ar- 

 cueil published in 1809, there appeared a paper 

 by that acute chemist, On the Combination of 

 Gaseous Substances with each other.* In this 

 paper he shows that the gases, considered in re- 

 spect of their volumes, unite with each other in 

 a very simple manner one volume of one gas 

 either combining with one volume, with two vo- 

 Inmes, or with half a volume of the other. Thus 

 one volume of carbonic acid gas combines with 

 one volume and with two volumes of ammonia- 

 cal gas ; fluoboric acid gas combines with one 

 volume and with two volumes of ammoniacal gas; 

 protoxide of azote is a compound of one vo- 

 lume azotic, and half a volume oxygen gas ; 

 deutoxide of azote of one volume of azotic, and 

 one volume of oxygen gas, &c. He proved also 

 in the same paper, that when gases unite, the 

 alteration of volume which they sustain, is al- 

 ways very simple. Deutoxide of azote is com- 

 posed of one volume of azotic, and one volume 

 of oxygen gas united without alteration of vo- 

 lume. Carbonic acid is composed of one volume 

 carbonic oxide, and half a volume of oxygen gas 

 condensed into one volume, &c. 



This very important view of the way in which 

 gaseous bodies unite, threw a new and unex- 



* Pag. 207. 



