IS 13.] the Hon, Henry Cavendish, 9 



mixture, the candle burnt 23'^ When the fixed air was ^th of 

 the whole, it burnt 11'^ When the fixed air was -X- or 

 of the whole mixture, the candle went out immediately. 



Mr. Cavendish conceived that the nature of the fixed air 

 given out by marble differed somewhat ; or that the elastic fluid 

 emitted consisted of two airs, one more absorbable by water than 

 the other. He drew his conclusion from the circumstance, that 

 after a solution of potash had been exposed to a quantity of fixed 

 air for some time, it ceased to absorb any more; yet if the 

 residual portion of air were thrown away, and new fixed air 

 substituted in its place, it began to absorb again. But Mr, 

 Dalton long after explained this seeming anomaly in a satisfac- 

 tory manner, by showing that the absorbability of fixed air by 

 water is proportional to its purity ; and that when mixed with a 

 great quantity of common air, or any other gas not soluble in 

 water, it ceases to be sensibly absorbed. 



Mr. Cavendish ascertained the quantity of fixed air contained 

 in marble, carbonate of ammonia, common pearlashes, and 

 carbonate of potash. But, notwithstanding the great precision 

 with which the experiments were made, these determinations are 

 of comparatively little value ; because the proper precautions 

 could not, in that infant state of chemical science, be taken, to 

 have these salts in a state of purity. The following were the 

 results obtained by Mr. Cavendish 



J 000 grains of marble contained 408 grains of fixed air. 

 1000 ....... .carb. of ammonia 533 



1000 pearlashes 284 



1000 carb. of potash .. 423 



Carbonate of potash was first obtained in^ the state of crystals 

 by Dr. Black. Mr. Cavendish formed it by making a solution 

 of pearlashes absorb fixed air till it deposited crystals. He 

 examined the properties of these crystals. They were not 

 altered by exposure to the air, did not deliquesce, and were 

 soluble in about four times their weight of cold water. 



Dr. M'Bride had already ascertained that vegetable and 

 animal substances yield fixed air by putrefaction and fermenta- 

 tion. Mr. Cavendish found by experiment that sugar, when 

 dissolved in water, and fermented, gives out of its weight 

 of fixed air, possessing exactly the properties of fixed air from 

 marble. During the fermentation no air was absorbed, nor was 

 any change produced upon the common air upon the surface of 

 the fermenting liquor. Apple juice fermented much faster than 

 sugar; but the phenomena were the same, and the fixed 

 air emitted amounted to -y^u of the weight of the solid extract 

 of apples. Gravy and raw meat yield inflammable air during 

 their putrefaction j the former in much greater quantity than the 



