196 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



taining a known volume of nitric oxide, and conversely. 

 He describes his experiments as follows : 



" The apparatus consists of a small bulb united to a 

 graduated tube by means of a capillary tube 6 centimetres 

 in length, divided into two equal parts by a tap . . . . " 



" The manner of procedure is as follows : Knowing that 

 the little bulb holds 170 parts of the graduated tube, I 

 introduced into it, after having made a vacuum, 160 parts of 

 nitrous gas ; I put then into the tube a definite volume of 

 oxygen, for example, 200 parts, and having opened the tap, 

 I find that 158 parts have entered the bulb. This has then 

 received 160 + 158 = 318 of gas: but its capacity being 

 only 170, there must have disappeared a volume equal to 

 318-170 or 148. Working thus and taking the mean of 

 several results, I found that for 100 parts of nitrous gas the 

 contraction is 94. 



" One cannot deduce from this experiment the quantity of 

 oxygen that is combined with the nitrous gas ; but if one 

 makes another experiment in which the oxygen disappears, 

 because the nitrous gas is in excess, and if one observes the 

 contraction, one will know the relationship in which the 

 oxygen and the nitrous gas are combined in each experiment, 

 assuming that the same product is formed, and consequently 

 that the contractions are the same in each case. For 

 example, I found that using 100 parts of oxygen and an 

 excess of nitrous gas, the contraction was 192. But since 

 in che first experiment a contraction of 94 corresponded 

 with 100 parts of nitrous gas, in the second experiment the 

 contraction of 192 should correspond with 204 of the same 

 gas. According to this, 100 parts of oxygen are combined 

 with 204 of nitrous gas, or, in round numbers, 200 ; and I 

 fix the contraction at 200 instead of 192, that is to say, I 

 make it equal to the volume of the nitrous gas or double 

 that of the oxygen." (" On the Combinations of Azote 

 with Oxygen," Ann. de Chimie, 1816, 1, 401 402). 



Gay-Lussac's figures showed that : 

 100 parts of oxygen combining with 

 204 parts of nitrous gas contract to the extent of 

 192 parts and give rise to 304 - 192 = 

 112 parts of the brown nitrous fumes. 



