3l6 , PHILOSOPHICAL TRANSACTIONS. [anNO I766. 



their weight of water, being dropt into a solution of chalk in spirit of salt, the 

 earth was precipitated, and an effervescence was produced. No precipitate was 

 made on dropping some of the same solution into a solution of Epsom salt, 

 though the mixture was kept upwards of twelve hours. But, on heating this 

 mixture over the fire, a great deal of air was discharged, and the magnesia was 

 precipitated. 



Part hi. — Containing Experiments on the Air produced by Fermentation and 



Putrefaction. 



Mr. M'Bride has already showed, that vegetable and animal substances yield 

 fixed air by fermentation and putrefaction. The following experiments were 

 made chiefly with a view of seeing whether they yield any other sort of air 

 besides that. 



Exper. I. — The air produced from brown sugar and water, by fermentation, 

 was caught in an inverted bottle of soap leys in the usual manner, and which 

 is represented in fig. 13. As the weather was too cold to suffer the sugar and 

 water to ferment freely, the bottle containing it was immersed in water, which, 

 by means of a lamp, was kept constantly at about 80° of heat. The quantity 

 of sugar put into the bottle was 93 1 grains: it was dissolved in about 6-i- times 

 its weight of water, and mixed with 100 grains of yeast, by way of ferment. 

 The empty space left in the fermenting bottle and tube together measured 1920 

 grains. The mixture fermented freely, and generated a great deal of air, which 

 was forced up in bubbles into the inverted bottle, but was absorbed by the soap 

 leys, as fast as it rose up. It frothed greatly; but none of the froth or liquor 

 ran over. In about 10 days, the fermentation seeming almost over, the vessels 

 were separated. The bottle with the fermented liquor was found to weigh 412 

 grains less than it did before the fermentation began. As none of the liquor ran 

 over, and as little or no moisture condensed within the bent tube, I think one 

 may be well assured, that the loss of weight was owing entirely to the air forced 

 into the inverted bottle; for the matter discharged, during the fermentation, 

 must have consisted either of air, or of some other substance changed into 

 vapour: if this last was the case, I think it could hardly have failed, but that 

 great part of those vapours must have condensed in the tube. The air remain- 

 ing unabsorbed in the inverted bottle of soap leys was measured, and was found 

 to be exactly equal to the empty space left in the bent tube and fermenting 

 bottle. It appears therefore, that there is not the least air of any kind discharged 

 from the sugar and water by fermentation, but what is absorbed by the soap 

 leys, and which may therefore be reasonably supposed to be fixed air. It seems 

 also, that no part of the common air left in the fermenting bottle was absorbed 

 by the fermenting mixture, or suffered any change in its nature from it: for a 

 small phial being filled with 1 part of this air, and 2 of inflammable air; the 



