62 



18240 grain measures of the first distilled air being forced into a bladder 

 holding about 21600, there was an increase of weight of 51 grains on pressing 

 out the air ; so that, allowing for the common air mixed with it, the pure fac- 

 titious air is lighter than water in the proportion of 13/ to 100. 



8160 grain measures of the 2nd distilled air being forced into a bladder 

 holding near 14000, it increased 4^ grains on pressing out the air, whence it 

 appears to be lighter than common air in the proportion of 171 to 100. 



The caput mortuum, consisting of the hartshorn burnt to a coal, weighed 

 623 grains. The weight of all the air discharged appears, from what has been 

 said, to be 5 1 grains, id est, -j^ part of the weight of the hartshorn, or about -^ 

 of the loss of weight which it suffered in distillation. 



We have examined, therefore, 3 substances of very different natures, namely, 

 the first a simple wood, the 2nd a vegetable substance of a saline nature, & 

 the 3rd an animal substance of the nature of bones. Each of them agreed in 

 furnishing some fixed & some inflammable air, but the proportions of these 

 airs were considerably different, & the nature of the inflammable air was not 

 quite the same in each, but yet hardly differing more than that produced from 

 the same substance at different periods of the distillation ; so that there 

 should seem to be a considerable resemblance between the air produced by 

 distillation from all animal & vegetable substances. 



In the first & 2nd experiments we have an examination of all the air which 

 can be procured from wainscot by distillation in close vessels ; but this is by 

 no means all the air which it contains ; for the caput mortuum, which, as was 

 before said, consists of the wood burnt to charcoal, seems to contain a verj'^ re- 

 markable quantity of fixed air. 



The alcali produced by deflagrating nitre with charcoal is well known to ef- 

 fervesce with acids, & consequently to contain fixed air ; which air, I think, 

 can proceed only from the charcoal ; for when nitre is alcalized by metals in 

 their metallic form, which contain no fixed air, the alcali makes no efferves- 

 cence with acids ; as I know by experience : & I think it seems very unlikely 

 that the nitre should furnish fixed air when deflagrated by charcoal, & not 

 produce any when deflagrated by metals. This induced me to make the fol- 

 lowing experiments. 



Exp. 6. 150 grains of the caput mortuum remaining after the distillation 

 of wainscot in the first & 2nd experiments, well dried, were ground with 5 

 times their weight of nitre and about 130 grains of water, & when the whole 

 was thought to be perfectly mixed, it was deflagrated by little & little in an iron 

 ladle. The intention of the water was to make the matter deflagrate with 

 less violence ; whereby there was less danger of any fixed air being dissipated 

 by the heat. The deflagrated matter was put into water to dissolve the alcali. 

 The insoluble matter, consisting partly of the ashes of the caput mortuum 

 & partly of some of the caput mortuum which had escaped the fire, weighed, 

 when well dried, 38 grains ; so that the loss of weight which the caput mor- 

 tuum suffered in deflagration was 112 grains. In order to find the quantity 

 of fixed air in the alcaline solution, 4 of it was saturated with the vitriolic 

 acid, & the loss of weight which it suffered in effervescence observed with the 

 same precautions as were used for finding the quantity of fixed air in pearl 



