of Determining Moisture and Carbonic Acid in Air, 309 



have been warmed above the temperature of the counterpoise, 

 the weighing must be deferred for half an hour, so as to allow 

 their temperatures to become equal again. The tubes are 

 weighed unstoppered. If several tubes are to be weighed 

 the stoppers * are removed before weighing from the whole of 

 the tubes, including the counterpoise, and not replaced until 

 the last tube has been weighed. No absorbent is kept inside 

 the balance-case. The tubes should be lifted by the wires 

 attached to them for hanging on the balance. 



We found the following form of aspirator very convenient, 

 especially when the apparatus had to be carried to a distance. 

 Two bottles (fig. 2), each holding about 3200 cub. cent, up to a 

 mark in the neck, were arranged as shown in the figure, and 

 connected together by a piece of stout, non-collapsing rubber- 



Fig. 2. 



tubing provided with a screw-clip for regulating the rate of 

 aspiration. The burette clips are for starting or stopping 

 the flow. The bottles are covered outside with a layer of felt, 

 to keep the temperature of the air and water equal during an 

 experiment, and also to prevent breakage. A vertical strip on 

 each bottle is, how r ever, left uncovered, so that the height of 

 the water may be w r atched during the experiment and the 



* The stoppers used are the ordinary ones, consisting of a short piece 

 of black rubber about f inch long, closed at one end by a piece of glass rod. 



Phil. Mag. S. 5. Vol. 29. No. 179. April 1890. 2 B 



