Chap. 2.] Pure Air from Silk, &V. 377 



and afcended to the top, but the air was in too fmali 

 3 quantity to be either meafured or proved. 



In thefe experiments it is probable that the oxygen 

 or pure air was extracted by an a6tual deccmpofition 

 of a part of the water, by means of a capillary attrac- 

 tion, aided by the folar influence ; and in effect the 

 fame philofopher was enabled to extract it, though in 

 a fmaller quantity, by means of a number of very 

 minute glafs tubes immerfed in water and expofed to 

 the^fun.- 



The properties or functions of this fluid are fome 

 of the moft important in nature ; nor, except caloric 

 o- heat, is there any natural agent more univerfal or 

 more active. 



i ft. It is elTential to combuftion ; nor do we know 

 of any procefs by which flame can be fupported with- 

 out a fupply of oxygen gas, or empyreal air. 



idly. In certain proportions it is abfolutely necefiary 

 to fuftain animal life j fo that the whole animal creation 

 may be faid to depend upon this fluid for their exift- 

 ence. 



3dly. Its bafis oxygen gives the acid character to all 

 mineral and vegetable falts, the bafes of which are found 

 to be entirely infipid till combined with oxygen. 



4thly. The calcination of metals is altogether effect- 

 ed by their union with oxygen. Thus for moft of the 

 mineral pigments, and a very numerous clafs of medi- 

 cines, we are indebted to this ufeful element. 



5thly. It forms a conftituent part of that necefFary 

 fluid, water, which confifts of 85 parts of oxygen, and 

 15 of hydrogen, or the bafis of inflammable air. 



Oxygen gas, or air, is more elaftic than common 

 air ; it exceeds it alfo in fpecific gravity, for the pro- 

 portion between pure and common air is as 160 to 

 152. 



On, 



