1348 



because the pressure then fciils below tlie three-pliase tension SSbO, 

 in other words the iiydrate can be decomposed. From the detei-- 

 minations of the fables 1 — 3 the three-phase pressure hvdrate-ice-gas 

 at — 80° can be calculated by extrapolation. When we assume the 

 heat of transformation to be independent of the temperature — it 

 has already been proved in § 5 that the influence of the temperature 

 is small — the following- equation is found for the three-phase line 

 SSbO b^ the aid of the tables i— 3 : 



1333 



loo P= 4- 6,7393. 



T 



When in this we substilnte /= --80°C., the pressure appears to 

 amount to 7 mm. In the carbonic acid-alcohol mixture the three- 

 phase tension may certainly not be neglected. In the filling of 

 the apparatus in ihe evacuation with cocoanul carbon we have, 

 therefore, to do both wilii slowly decreasing adsorption, and with 

 decomposition of the hydrate, ll ap[)ears from the aiiove-described 

 observations that the time of evacuation can easily be chosen so 

 that neither has a disturbing intluence in the determinalion of the 

 equilibrium pressures. 



Decomposition of the hulrate shoidd, however, be avoided in the 

 direct analysis. The |)ressure of the walerjet pump lies sufficiently 

 high abo\e the three-phase piessure, that decomposiiion may be left 

 out of account ; uniier the^e circumstances the adsoi'ption can, 

 however, no! be abolished in a few hours, improvement in the 

 direct analysis method is oidy possible by choosing the time of 

 evacuation longer. We have still performed three direct analyses in 

 the way described above (cf. § 1 loc. cit.). in which the time during 

 which the hydrate remained connected with the waterjet pump, 

 was carried iq) to 5 (one determination) i-esp. 7 (two determinations) 

 hours. Notwithstanding Ihis these detei-minalions yielded for the 

 water content 5.39, 5.46, and 5.61 H,(). Only the last value falls 

 somewhat outside the limits 5.1 lo 5.5 of the determinations 

 performed before ^see § 1). Accordingly the value 6 is far from 

 being reached heie eithei-. 



The gas-adsorption discussed here is, therefore, the cause that the 

 sulphuretted hydrogen hydrate has not yet been prepared by a direct 

 way in pure stale, and thai il cannot be analysed either, but ihat 

 an indirect method which can be applied here at temperatures where 

 this adsorption is no longei' active, yields the right conqiosition 

 for this substance. At these tenq)ei-atures direcl analysis is, however, 

 impossible on account of the great tension of dissociation. 



Delft— Amsterdam, March 22, 1919. 



