

of Determining Moisture and Carbonic Acid in Air, 307 



hitherto lies in the fact that for an accurate analysis a very- 

 long period of experiment is necessary. The changes in the 

 amount of moisture which in ordinary cases occur during 

 the period of experiment are thus not indicated, and the 

 method is rendered useless for many purposes, besides being- 

 very inconvenient. 



The details of the method have recently been reinvestigated 

 by Shaw, in a research undertaken at the request of the 

 Meteorological Council*. He found that with a U-tube filled 

 with pumice and sulphuric acid and weighing about 170 

 grammes, the absorption was complete with a rate of aspira- 

 tion of about 8 or 10 litres per hourf. With double this 

 rate there was a considerable escape of moisture through the 

 first absorption-tube J. Thus, with the faster rate of aspira- 

 tion, the increase of weight of a second absorption-tube had 

 to be added to the result. But since it was found that be- 

 tween the weighings the second tube frequently varied con- 

 siderably in weight from accidental causes, the advantages of 

 the faster rate were neutralized. 



We have endeavoured to improve the method in three 

 directions :— (1) by reducing to a minimum accidental varia- 

 tions in the weight of the tubes ; (2) by increasing the 

 efficiency of the absorbing tubes, and thus making a very 

 rapid rate of aspiration possible ; and (3) by making the 

 apparatus more convenient. 



Fig. 1. 



OL CI ll tt 



Absorption apparatus for Moisture and Carbonic Acid, Xh 



a. Tubes filled with pumice soaked in sulphuric acid, b. Tube filled with 



soda-lime. c. Plug of cotton wool. 



The absorption apparatus which we finally adopted is shown 

 in fig. 1. We shall describe it in detail because, as will be 

 * Phil. Trans, vol. A, 1888, p. 73. f Ibid. p. 81. t IM& p. 8a 



