108 



DE. B. D. STEELE, DE. D. McINTOSH AND DE. E. H. AECHIBALD 



TO PUMP 



in which - P - represents the change of vapour-pressure with temperature, P the 



(/ A 



pressure, T the absolute temperature, R the constant of the gas equation, and W the 

 latent heat of evaporation of one gram-molecule of the liquid. 



The values of W at a pressure of 760 millims., as calculated from our vapour- 

 pressure curves, are 



for hydrogen chloride, 14'8 x 10 10 ergs, 



bromide, 17'4xl0 10 



iodide, 207 xlO 10 



sulphide, 19'3xl0 10 



phosphuretted hydrogen, 17 '2 x 10 10 ,, 



We can find no account of any direct determination of W for these substances. 



The Measurement of Density. 



The apparatus (fig. 4) employed for these measurements consisted of a bulb with a 

 graduated capillary stem, to which a two-way stop-cock c was attached. 



The bulb had a capacity of about 1*5 cub. centim., and 

 its volume and that of each division of the stem was 

 accurately determined by calibration with mercury. After 

 the tube a had been sealed to the pump, and the apparatus 

 exhausted, it was immersed in the constant-temperature 

 bath. The tube b was then connected to a vessel con- 

 taining the liquefied gas, which was distilled into the bulb 

 until both bulb and stem were completely filled. The 

 stop-cock was turned and the liquid allowed to evaporate 

 into the pump until the meniscus had come to a definite 

 position on the stem, when the stop-cock was turned so 

 as to disconnect all the tubes. To obtain the volumes 

 occupied by a constant weight of liquid, it was only 

 necessary to read the position of the meniscus at different 

 temperatures. 



The weight of liquid was obtained by attaching to the 

 Fig. 4. tube b a weighed set of GEISSLER'S bulbs containing 



potassium hydrate solution. 



On opening the stop-cock and raising the temperature of the bath the liquid 

 evaporated and the gas was absorbed in the bulbs and weighed. 



To prevent the potash solution sucking back, a little mercury was placed in the 

 first bulb. The small amount of gas remaining in the apparatus was finally pumped 

 out through a and measured. 



<i 



