i chick are evolved in Coal-Mines 137 



At the time of weighing the full balloon, the barometer 

 stood at 27-907 In. 



From this, however, is to be deducted the 

 height of the inner level of the water in the re- 

 ceiver above the outer, since, after the passage 

 of the gas from the receiver to the exhausted 

 balloon, the water rose. This column of water, 

 reduced to a column of mercury, gives . 0.62 



27.287 In. 

 Barometer under the receiver, . . . 0.375 



Therefore tension of the weighed air, . 26.912 



Temperature, 57°.2 F. 



The weight of the pit-gas at 32° F., and 28 inches B. is 

 therefore = 60.304. 



In the correction of the aerostatic influence, s and e have not 

 been taken into consideration, because, during the two experi- 

 ments, the quantity of atmospherical vapour was not percep- 

 tibly altered. The condensation always ensued at 26°. 5 F. 



The specific gravity of the pit gas is therefore — - = 



1 ° l B 104539 



0.576856. 



A second experiment gave 0.571667. 



Inasmuch as the balloon was twice filled with the pit-gas, 

 the quantity of the atmospheric air still left behind must have 

 been so small as to be indeterminable. As, however, every 

 gas is rendered impure by atmospheric air when the water by 

 which it is retained stands in free communication with the 

 atmosphere, the pit-gas, previous to its entrance into the 

 balloon, must have been rendered more or less impure by at- 

 mospheric air. In order to be able to estimate and deduct this 

 air, a little gas was expelled from the balloon by gentle heat. 



The determination of the small quantity of oxygen in this 

 gas was attended with difficulty. I tried in vain the employ- 

 ment of a solution of sulphuret of potassium. Two experi- 

 ments with the gas from the balloon afforded a mean of ab- 

 sorption of 0.05765 vol., while, on the other hand, experi- 

 ments with pure pit- gas ;ifforded an absorption of 0.0576 v. 

 The sulphuret of potassium had therefore absorbed some 

 of the pit-gas itself. ^Compare § 1 in vol. xxix, p. 316). Nitric 



