218 PROCEEDINGS OP THE AMERICAN ACADEMY 



is established throughout the whole apparatus, which may then be left 

 to take care of itself. If the current does not exceed in rapidity 

 two bubbles a second, it may be allowed to flow for twenty-four hours 

 without risk, and in that time every trace of carbonic acid will have 

 been washed out of the 'balloon. The suction should now be stopped, 

 and the cocks of the balloon closed. The tubes A, B, and C may 

 then be disconnected, and after they have come to equilibrium in the 

 balance case reweighed. The double bulb E must also be discon- 

 nected, the baryta washed out into a suitable bottle, and the solution 

 retitrated with oxalic acid. 



As the weights of the tubes A, B, and C must be corrected for 

 the buoyancy of the air, it is essential to note the temperature of the 

 balance case and the height of the barometer at the time of each 

 weighing. The corrections in question may be considered under 

 two heads ; first, that made necessary by a change of temperature or 

 pressure between successive weighings ; secondly, that required to 

 eliminate the effect of atmospheric buoyancy on the total weight of 

 carbonic acid absorbed. 



The first correction is best made by the method already described, 

 and the application of this method was greatly facilitated in the 

 present investigation by the circumstance that the same tubes, wiih 

 the "same weights of contents, were used in all the carbonic acid 

 determinations made. We were able to determine once for all for 

 each tube the correction required for a variation of one tenth of an 

 inch in the barometric height reduced to 27° C.,* and then the cor- 

 rection in any case could be found by a simple multiplication. Thus 

 we estimated that the correction for one tenth of an inch in the 

 barometric height reduced to 27° C. was, — 



For the potash bulb before absorption, . . . 0.306 milligram. 



« " after " ... 0.321 " 



" soda lime tube 0.067 " 



" phosphoric anhydride tube .... 0.040 " 



* That is, reduced to the height which would be required to give at the 

 temperature of 27°, an atmosphere of the same density and buoyancy as that 

 at the temperature of the balance case when the tube was weighed. These 

 Proceedings, vol. xix. p. 55. 



