tin- explosion. it is found that the volume of the water formed is eju;il to 

 two-thin Is i- that is. it is equal to the volume of the hydrogen contained 

 in the \vattT. ( 'on sequent 1 v, the \ olumet ric com posit ion of water should 

 IK- expressed in the following terms: Two volumes of hydrogen 

 combine with one volume of oxygen to form t wo volumes of aqueous 

 vapour. For substances which are gaseous at the ordinarv tempera- 

 ture. this direct method of observation is sometimes very easilv con- 

 ducted : for instance, with ammonia, nitric, and nitrous oxides. Thus 

 to determine the composition by volume of nitrous oxide, the above- 

 described apparatus may be employed. Nitrous oxide is introduced 

 into the tube, and having measured its volume a series of electric 

 spark- are passed through the gas, and it is found that two volumes of 

 nitrous oxide give three volumes of gases namely, two volumes of 

 nitrogen and one volume of oxygen. Consequently, the composition of 

 nitrous oxide is similar to that of water : two volumes of nitrogen and 

 one volume of oxygen give two volumes of nitrous oxide. J>y decom- 

 posing ammonia it is found to be composed in such a manner that two 

 volumes give one volume of nitrogen and three volumes of hydrogen ; 

 ;d-o. two volumes of nitric oxide are formed by the union of one volume 

 of oxygen with one volume of nitrogen. The same mav naturally be 

 proved bv calculation from the vapour densities, as was described above ; 

 hence the composition by volume of vapours may be determined in the 

 simplest manner, if their density, composition, and the densities of the 

 component parts are known. Thus, according to Thomsen, the density 

 of N<) referred to hvdrogen 15, and it contains 14 parts of nitrogen, 

 and 1; parts of oxygen in l\0 parts : hence the volumetric composition 

 is 1 volume of nitrogen and 1 volume of oxygen in '2 volumes of 

 nit ric oxide. 



Comparisons of various results made bv the aid of direct observa- 

 tion.- or calculation, an example of which has just been cited, led (Jay- 

 LUS-U.C to the conclusion that flu' rnlnitu' (>/'</ coinnonii'l in <> i/nmoim or 



,n, -I, (,/' //if <-,,in i>n< at ji ft* <>/' irfiii'fi if ixftirntvil (and consequently 

 tin- -inn of the \olumes of t he eleli MM 1 1 s of \\hicll it is for! ..... 1). This 

 the 



