648 PHILOSOPHICAL TRANSACTIONS. [aNNO 17Q0. 



the blood in the act of respiration, but only that dephlogisticated air enters into 

 it. But that Dr. P.'s former supposition, as well as Dr. G.'s, is true, will appear, 

 he presumes, from the experiments which he will presently recite. 



As, in order to determine what proportion of the dephlogisticated air destroyed 

 by respiration is employed in forming the fixed air which is the produce of it, it 

 was necessary to ascertain as exactly as possible the proportion of dephlogisticated 

 air and of phlogiston in the composition of fixed air. Dr. P. repeated with parti- 

 cular care experiments similar to those he had formerly made for that purpose. 

 He heated charcoal of copper in 41 oz. measures of dephlogisticated air of the 

 standard of 0.33, till it was reduced by washing in water to 8 oz. m. of the 

 standard of 1.33. Again, he heated charcoal of copper in 40.5 oz. m. of de- 

 phlogisticated air of the standard of 0.34, till it was reduced to 6 oz. m. of the 

 standard of 1. 70. And in each of these cases there was a loss of 6 gr. of the 

 charcoal of copper; so that there cannot be more than 6 gr. of phlogiston in 33 

 oz. m. of fixed air, and consequently that only a very little more than -i- of the 

 weight of fixed air is phlogiston. He also heated perfectly well burnt charcoal 

 of wood in 6o oz. m. of common air, and found -^ of the remainder to be fixed 

 air, and the residuum of the standard of 1.7. Lastly, he heated 8^ gr. of per- 

 fect charcoal in 70 oz. m. of dephlogisticated air, of the standard of 0.46, when 

 it still continued 70 oz. m.; but after washing in water it was reduced to 40 oz. 

 m. of the standard of 0.6, and the charcoal then weighed Hgr.; so that from 

 this experiment with common charcoal, as well as from the preceding with char- 

 coal of copper, it appears, that about -f of the weight of fixed air is phlogiston, 

 and consequently that the other 4 are dephlogisticated air. 



Having done this, he proceeded to ascertain how much fixed air was actually 

 formed by breathing a given quantity both of atmospherical and of dephlogisti- 

 cated air, in order to determine whether any part of it remained to enter the 

 blood, after forming this fixed air. For this purpose he breathed in 100 oz. m. 

 of atmospherical air, of the standard of 1.02, till it was reduced to 71 oz. m. 

 and by washing in water to 65 oz. m. of the standard of 1.45. When the com- 

 putations are properly made, as directed in a former paper, it will appear, that 

 before the process this air contained 67.4 oz. m. of phlogisticated air, and 32.6 

 oz. m. of dephlogisticated air; that after the process there remained 53.105 oz. 

 m. of phlogisticated air, and 11. 895 oz. m. of dephlogisticated air; and that 

 there were only 6 oz. m. of fixed air produced; for the quantity absorbed during 

 the process could only have been very inconsiderable. It will therefore be evi- 

 dent that, in this experiment, 20.7 oz. m. of dephlogisticated air, which would 

 weigh 12.42 gr. disappeared; whereas all the fixed air that was found would only 

 have weighed 4.4 gr., and ^ of this being phlogiston, the dephlogisticated air 

 that entered into it would have weighed only 3.3 gr.; consequently 9. 12 gr. of it 



