34 On the doctrine 



dephloglftlcated air which thefe fubflances contain is then 

 extricated ; but if the foUitions be evaporated, and the dry 

 refiduum be heated by a burning lens, the pure air is 

 evolved. For the common air in which they are heated 

 receives an addition of pure air. But the reverfe is the 

 cafe when the folutions of finery cinder or flowers of 

 zinc are treated in the fame manner. 



I heated a folution of the piu'cft flowers of zinc in 

 marine acid in common air, and obferved that it emitted 

 a denfe white vapour for about an hour after it was eva- 

 porated to dryneis. The air was but little diminifhed, 

 but Vv'orfe than common air, in the proportion of 1.45 



to 1.35- 



I have obferved that common air which has been cx- 

 pofed to hot charcoal is both diminilhed and phlogifli- 

 cated, but that the air which by immerfion in water 

 comes out of this charcoal is Ilkewife phlogifticatcd. 

 This proves the generation of phlogifticatcd air in the 

 procefs. The water over which this procefs is made alfo 

 gives out air lefs pure than that of the atmofphere. 



Charcoal that had been expofed in common air under 

 a receiver fome days, did not, when immcrfed in water, 

 give out more than half as much air as charcoal heated 

 and put into water immediately after it was cold. Both 

 being placed near the fire, ftill imrherfed in water, gave 

 out more air, but in the fame proportion. Alfo, ftand- 

 ing in this fituation a long time made no difference in 

 this cafe. 



6. That finery cinder contains nothing but water and 

 calx of iron, I think I have fufiiciently proved by feveral 

 obfervations, efpecially by its enabling hot charcoal to 

 give out the fame kind of air that water will do. I had 

 a finiilar refult with terra ponderofa aerata^ which gives 

 no fixed air with mere heat, but does it when red hot by 

 means of water. 



I mixed 



