150 EESEAKCHES UPON THE CHEMICAL PROPERTIES OP GASES. 



the introduction of the various forms of apparatus proposed by Hempel and Winkler 

 has tended to greatly simplify quantitative gas analysis. 



The majority of absorption gasometric methods are based upon the assumption 

 that the contraction undergone by the volume of a gas on exposure to a liquid reagent 

 is not only a measure of the percentage of a particular constituent of the gas mix- 

 ture, but that the identity of such constituent is established by the same operation. 

 This assumption is very often warranted by the facts, but occasionally leads to error. 

 Qualitative methods, for the recognition of diflPerent gases, have usually been held 

 wholly subordinate to quantitative absorption or explosion methods. Quantitative 

 analyses are far more reliable if the constituents to be determined can be positively 

 identified by independent methods ; and it is somewhat strange that, heretofore, the 

 qualitative side of gas analysis should have received so small a share of attention. 

 In the following work, an attempt has been made to collect together the more impor- 

 tant reactions of the commonly occurring gases. The results must be regarded as 

 a first attempt only, inasmuch as improved methods of preparation and purification 

 will doubtless involve the necessity of corrections in certain cases. Accurate methods 

 of qualitative gas analysis are likely to prove of increasing importance in the study 

 of the atmosphere, in the laboratory and in the chemical arts. The following sub- 

 division of the subject has been found convenient : 



1. Phenomena of oxidation of hydrogen and hydrocarbons by air in presence of 

 finely divided metals and other oxidizing agents. 



2. Reactions of gases towards various metallic salts and other compounds used 

 in solution, and in a dry state at high temperatures. 



