1903.] The Evaporation of Water in a Current oj Air. 75 



The stirring arrangement S, fig. 1, consists of a vertical glass tube, 

 terminating in a horizontal T-piece open at both ends. In the 

 vertical tube is an opening a little below the surface of the liquid. 

 The T-tube was rotated about a vertical axis by means of a hot-air 

 engine. The circulation of the water in the thermostat was found to 

 be very effective when the T-piece made three revolutions a second. 



(2) The wash-bottles, W, fig. 1, were each of about 100 c.c. capacity, 

 and were all sealed together (except in some of the earlier experiments) 

 in order to prevent leaks and the access of grease or other foreign 

 matter. The last flask through which the air passed was connected 

 with a pressure-gauge GI (read by a mirror scale) by a tube with a stop- 

 cock just above the bath. 



(3) The absorption apparatus, B, fig. 1, which was connected with 

 the tube from W by a ground-glass joint J, consisted of two small 

 wash-flasks containing pure concentrated sulphuric acid ; about 10 c.c. 

 were placed in the first flask and 2 c.c. in the second. In the earlier 

 experiments the two flasks were connected by rubber tube, and weighed 

 separately, but it was found that the second never gained more than 

 1 mg. during an experiment, and they were therefore sealed and 

 weighed together. As a further proof of the completeness of the 

 absorption, in two experiments at 80 a tube containing phosphoric 

 anhydride was connected up with the second bulb, but it did not 

 increase in weight by so much as 0*1 mg. 



(4) The aspirator consisted of a large bottle, H, fig. 1, placed in a 

 large pan of water. For the experiments at the lower temperatures 

 the bottle had a capacity of 12 litres, but for some of the higher 

 temperature experiments a 4-litre bottle was employed. The quantity 

 of water outside was so large that the temperature did not change 

 more than 0'1 during an experiment, and hence a regulator was con- 

 sidered unnecessary. Water was drawn off through the tube U into 

 graduated flasks. The pressure of the air in the bottle H was read by 

 means of a gauge, G2. Between the joint J and the bath, the 

 projecting tube was surrounded by sheet brass and heated by a 

 row of small gas jets (in the earlier experiments by a coiled 

 wire, through which an electric current was passed), in order 

 to prevent condensation of vapour in this part of the tube. The 

 three-way stop-cock C was the dividing line between the flasks 

 containing the water and the absorption apparatus ; by means of it 

 connection could be made between two U-tubes (not shown in the 

 figure), containing strong sulphuric acid, and the absorption apparatus, 

 so that the tube between B and C might be cleared of moisture by a 

 current of air from the outside, passing first through the U-tubes. 



Between the absorption apparatus and the aspirator were a calcium- 

 chloride tube, Ca, and two small wash-bulbs containing water, the 

 former to prevent water vapour from getting back to the absorption 



