142 HEATING, 



namely, ammonia, composed of unconsumed hydrogen and a 

 portion of the nitrogen liberated from the air. Thus we have a 

 double motive for providing against the escape, unconsumed, ol 

 the hydrogen of the gas. 



What, then, is to be done ? Let us complete this second 

 process as we did the first : let us supply this hydrogen, this 

 remaining 80 per cent, in volume of the gas, with its own proper 

 equivalent of oxygen, as we did in the case of the carbon. 



But what is this second equivalent ? By the same laws of 

 definite proportions, we learn that the saturating equivalent of 

 an atom, or any other given quantity of hydrogen, is, not double 

 the volume, as in the case of the carbon, but one half its volume 

 only — the product being aqueous vapor, that is, steam; the 

 relative weights of the combining volumes being 1 of hydrogen 

 to 8 of oxj^gen ; and the bulk, when combined, being two thirds 

 of the bulk of both taken together, as shown in the annexed 

 figure 8. ^ 



We thus find, that to saturate the one volume of carbon vapor, 

 two volumes of oxygen are required ; whereas, to saturate the 

 two volumes of hydrogen, one volume only of oxygen is required : 

 thus, 



FIRST CONSTITUENT. 



Carbon. Oxygen. 



Vol. Atom. Weight. Vol. Atom. Weight. Vol. Atom. Weight. 



i . . 1 . . .6 unite with 1 . . 2 . . .16 forming ) i -j 92 



carbonic acid. | 



SECOND CONSTITUENT. 

 Hydrogen. Oxygen. 



Vol. Atom. Weight. Vol. Atom. Weight. Vol. Atom. Weight. 



2 . . 2 . . .2 unite with 1 . . 2 . . .16 formins: ' 



steam. 



2 . . 2 . . .18 



Here we see, that, in the case of this first constituent, as 

 above, the half volume of carbon and one volume of oxygen 



* Professor Brande puts this so clearly that I here give his own 

 M'ords : — ''The simple ratio which the weights oi the combining ele- 

 ments bear to each other involves an equally simple law in respect to 

 combining volumes, where substances either exist, or may be supposed 

 to exist, in the state c^f gas or vapor. 



" Thus, w'ater may \)e considered as a compound of 1 atom of hydro- 

 oen and 1 atom of oxygen, the relative weights of which are to each 



