294 
the blood. Hence, therefore, when black blood is 
reddened by the air, through the coats of a moistened 
bladder, the air yields no oxygen to the blood, nor 
acquires from it any carbon ; but the carbon of the 
bladder, by its combination with the oxygen of the 
air, passes into the state of carbonic acid gas. 
588. Even Dr Priestley, who neglected to observe 
the effects produced in atmospheric air, by the con- 
tact of bladders, was well aware of the action they 
exerted on nitrous gas, which we now know to be 
composed of the same elements as common air. He 
observed an incrustation of lime to appear, when 
nitrous gas, which had been previously kept in a 
bladder, was mixed with lime water ; or, when this 
gas was transferred from one vessel to another 
through a bladder, it produced a similar effect. To 
prove that this effect arose from the bladder, he put 
a bladder into a jar of nitrous gas, and, after it had 
continued there twenty-four hours, he transferred 
the gas into a glass-vessel of lime-water, which it 
rendered turbid *. In other experiments, when ni- 
trous gas was left in moistened bladders, it complete- 
ly lost its property of diminishing common air ; but 
if the bladder was kept quite dry, the gas then under- 
went little or no change f. He even found that nitrous 
gas was, in like manner, deprived of its oxygen, by 
being placed in contact with blood, by which it was 
rendered unfit for eudiometrical purposes |. 
589, The remarks, which have now been made, 
* Obs. on Air, vol. i. p. 213. 
t Obs. on Air abridged, vol. iii, p. 389. J Ibid, p, 367. 
