294 ^^' PiiiESTLEY^s Experiments and Ohfervations 



Notwith Handing the above-mentioned variations, the lofs of 

 weight in the charcoal was always much exceeded by the weight 

 of the water expended, which was generally more than double 

 of the charcoal ; and this water was intimately com.bined with 

 the air ; for when I received a portion of it in mercury, no 

 water was ever depofited from it. 



The experiment which, upon the whole, gave me the moft 

 fatisfaclion, and the particulars of which I fhall therefore re- 

 cite, was the following. Expending 94 grains of perfe(5l 

 charcoal (by which I mean charcoal made with a very ftrong 

 lieat, fo as to expel all fixed air from it) and 240 grains of 

 water, I procured 840 ounce meafures of air, one-fifth of 

 which was fixed air, and of the inflammable part nearly one- 

 third more appeared to be fixed air by decompofition. 



Receiving this kind of air in a variety of experiments, but 

 not in the preceding ones in particular (for then I could not 

 have afcertained the quantity of it) confiding of fixed and in- 

 flammable air together, I found fome variations in its fpecific 

 gravity, owing, I imagine, to the ditterent proportions of 

 iixed air contained in it ; but upon the whole, I think, that the 

 proportion of 14 grains to 40 ounce meafures is pretty near the 

 truth, when the proportion of fixed air is about one-fifth of the 

 whole. With refpe£l to the weight of the inflammable air after 

 the fixed air was feparated from it, I found no great difi^erence, 

 and think it may be eftimated at 8 grains to 30 ounce meafures. 



Upon thefe principles, the whole weight of the 840 ounce 

 meafures of air will be - 294 grains 



that of the charcoal will be 94 

 that of the water - 240 



334 which, confidering the na- 



7 ture 



