W. N. SHAW ON HYORO1IETRIC METHODS. 87 



was easily slipped through a piece of thick india-rubber sheet forming a stopper to 

 the 3-inch glass cylinder, and the other end, having the tube and thermometer very 

 close together, was enclosed by half slitting an india-rubber bung previously carefully 

 drilled, the slit passing along the common diameter of the two drilled holes; the 

 half slit bung was then slipped on the tube and thermometer, carefully pressed 

 together with shellac varnish, and the bung coated with varnish and pressed home. 

 It is perhaps surprising that there was no leak, but repeated tests showed that the 

 DINES was in this way fixed air-tight in the cylinder. At first a leakage took place 

 where the blackened glass of the instrument was fixed into the metal box. This was 

 closed by painting round the edge with a solution of india-rubber in benzene, and 

 after a good thick layer had been formed it was varnished with shellac varnish. 



These dew-point instruments were sometimes excluded, the REONAULT by with- 

 drawing the hygrometer and filling up the neck of its globe with a bung, the DINES 

 by removing the cylinder altogether. 



All the connexions between the different parts of the apparatus were made by glass 

 and very short pieces of india-rubber tubing carefully wired and varnished. 



The rest of the apparatus was similar to that already described, but was modified 

 in the following details : 



i. The saturator. This was required to saturate air at a temperature below that of 

 the room. For this purpose a large galvanized iron water tank jacketed with 3 inches 

 of sawdust in a second galvanized iron tank was introduced to form a bath in which 

 the saturator could be completely immersed. The saturator proper will be understood 

 by reference to fig. 5. The glass tube a was open to the external air, and led to a 

 spherical glass vessel, b, filled with moist sponge ; from this vessel a bent glass tube, c, 

 led through a cork to the interior of the copper cylindrical vessel, V, through a metal 

 lid bolted to it, and made air tight by an india-rubber washer round the rim. The 

 vessel V was loaded with shot so that the whole apparatus just sank in water, and 

 above the shot was a thin glass cylinder containing a layer of water at the bottom, in 

 which stood a wire frame covered with well- washed muslin. The tube C opened into 

 the vessel V outside the muslin frame, but inside the glass. The air was drawn out 

 of the interior of the vessel through the tube d, close to which was the bulb of a 

 thermometer ; the tube d was the extension of a glass three-way tap T, which was 

 fixed just outside the copper vessel ; by it I could send air through the rest of the 

 apparatus without its passing through the saturator, and thus dry the connecting 

 tubes, Ac., when necessary. This part of the apparatus was immersed in water, in 

 the final experiments so that the tap was covered (the projecting nozzle being 

 extended by an india-rubber tube), in the tank already spoken of, and the temperature 

 of the water therein was reduced by stirring ice in it to any required extent. 



ii. The drying tubes. Two sulphuric acid or two phosphoric acid ones were used 

 for the observations. These remained as before, except that the connexions (see 

 fig. 1) between them were made by glass tubes and shortened as much as possible. 



