Specific Gravity of Vapours and Gases. 11 



atmospheric air and the gas to be investigated are separately led 

 through the caoutchouc tubes a, a, and, after being dried in the 

 chloride-of-calcium tubes d, d, pass out at the exit tubes c, c. They 

 then pass by means of two of the capillary glass tubes (iig. 5), 

 which fit air-tight into the connectors c, down to the bottom 

 of the vessels, through their somewhat wider capillary necks. 

 In order to do this safely and conveniently, the glass thread 

 is laid on the board b, which is of the same inclination as the 

 thermostat, and then allowed to glide into the glass vessel ; 

 its pliability allows it then to be readily connected with the 

 drying-tube d by means of the caoutchouc connector c. When 

 the atmospheric air has been completely driven out of the 

 vessel by the dried gas, the glass thread is, in the same way as 

 before, withdrawn. If this is done slowly, and the gas is heavier 

 than air, enough flows from the wide part of the glass thread, 

 out at its lower end, to replace the space in the vessel occupied 

 by the glass thread before its removal. But even when this is 

 not the case, a serious error is not to be apprehended, since the 

 volume of the glass vessel 176 cub. centims., compared with that 

 of the glass thread by which these 176 cub. centims. would 

 be diminished, amounts only to O09 cub. centim. ; so that the 

 error would amount to not more than yo,%o o °^ ^ e volume of the 

 gas. 



If the apparatus is used for vapour-density determinations, 

 then dry atmospheric air is led, in the way just described, into 

 the proper vessel, and the liquid whose vapour is to be examined 

 is poured into the vessel used for gases by means of a funnel 

 with a capillary stem ; it is then placed in the thermostat. The 

 capillary tube projecting from the thermostat is then provided 

 with the arrangement represented at B, fig. 3, which is intended 

 to regain the evaporated liquid without loss, and also to form a 

 self-closing stopper which can cut off the* interior of the vessel 

 from the outer air. Fig. 6 shows the arrangement in its details. 

 a is a thick platinum-wire which does not quite fill up the capil- 

 lary of the vapour- vessel ; b a tube pushed over both platinum- 

 wire and capillary, serving to lead off the vapours. When the 

 stream of vapour enters from /into the wider tube b, it causes a 

 suction of air at the opening of the tube c, which effectually 

 prevents the dropping away of liquid from that point; d is a 

 solid copper wire placed in front of the cork, hammered out at 

 d } and fitted closely round the glass tube, while it is kept in 

 position by the little weight /3. By means of the moveable side- 

 lamp attached to the thermostat, this copper wire is heated to 

 such a point that a hissing noise is produced when it is moistened 

 at d with a drop of the fluid which is being experimented on. 



This heated wire prevents the condensation of liquid in and 



