ÏUn 



The situation of the quadruple point could be founiJ by graphically 

 determiiiing the point of intersection of the (wo three-phase lines 

 SSbO and SLdi. In this way by the aid of the data recorded in the 

 tables J— 6 we find / = — 0.6±0.2; the corresponding pressure 

 amounts to about 70 cm. of mercury. The quadruple point tempera- 

 ture can, however, be calculated more accurately as follows. 



Under the circumstances of the quadruple point the liquid A, is 

 a diluted solution of sul|)huretted hydrogen iu water. When a again 

 represents the number of volumes H^S of one atmosphere (corrected 

 for 0°), which dissolves in one volume of water, the nuujber of 

 gramme-molecules /7,-S that dissolves iu 100 grauimes of water, is 

 5.87.10 '^ aJ\ If H-^S were a uon-electrolyte, the lowering of the 

 freezing-point would accordingly amount to 5.87.10-'^ r//^. 18.0°. When 

 in this we introduce for a and P the solubility at ^ = — 0.6° (4.709) 

 and the quadruple point pressure found graphically (70), we find a 

 lowering of the freezing point of 0.4°; the quadruple point tempera- 

 ture amounts, therefore, to —0.4° C. When for n the solubility at 

 — 0.4° is chosen, this brings no change in the calculation. 



Nor does the fact that sulphuretted hydrogen in water is partially 

 electrolytically dissociated bring a change in the above calculation. 

 The dissociation constant of H.^S amounts (first stage) to about 

 iO-'. The dilution under the circumstances of the four-phase equili- 

 brium amounts to 5.2, the degree of dissociation in consequence of 

 this to about 7.10^, and consequently the latter has no appreciable 

 influence on the situation of the quadruple point. 



In order to find the value of E^ at this temperature, the specific 

 heats of the reacting substances must be known. As the molecidar 

 specific heat of the hydrate (/i = 6) would amount to 61.6 according 

 to the law of Kopp '), and as the specific heat of six molecules of 

 water and one mol. of sulphuretted hydrogen is 108 -|- 6.3 = 1 14.3. 

 the algebraic sum is about 53. The correction required for the 

 calculation of E^ at the quadruple point is, therefore, 53 (^ -|- ^^•4)- 

 The mean of the values thus found is recorded in the last column 

 of the tables 4—6. 



The values of tlie last colunui but one in tables 4 and 5 still 

 present appreciable deviations. This is owing to the small differences 

 of temperature between the smressive oftservations. In order to 

 determine these diflerences uiure accurately the ANscHÜTZ-thermo- 

 meter (division i)ito ' ^ degree), which was used in the other 

 determinations, was replaced by a BKCKMANN-lhermometer (division 



Nernst. Tlieoi-etische Cheinie. Gesetz von Duloinü und Petit. 



