667 



accurately, I iiave adjusted a wide cylindrical \e8sel narrowed at 

 the lower end round the test tube, in which vessel alcohol was 

 stirred by means of vertically moving leaden plates; the heating took 

 place electrically; cooling was effected by introduction of solid 

 carbonic acid. In the observations with small volume it now appeared 

 that the maximum temperature at which the compound can exist 

 by the side of gas, is about 18°. The quadruple point lies at this 

 temperature; the pressure is about 52 atmospheres. In this point 

 there is intersection of the three-phase lines S (compound), L^ (liquid 

 rich in carbonic acid), and G (gas), which is stable at temperatures 

 below the quadruple point, and cannot be prolonged above the 



dp 



quadruple point, S -(- L, -|- G, which exhibits a value of ^, which 



(/ 7' 



rapidly increases with the tempeiature in the neighbourhood of the 

 quadruple point, Lj -)- L^ -)- G, which indicates stable equilibria 

 above the quadruple point, but can aKso be easily determined below 

 the quadruple point; then these equilibria are, however, metastable 

 with respect to the solid phase. The fourth three-phase line 

 S 4- Li -(- Lj rapidly moves from the quadruple point to higher 

 pressure. The situation of the three-phase lines is indicated in fig. 1 

 by the letters given above; the quantitative data have been collected 

 in table I; they have been obtained with two mixtures; one 

 contained a great, the second a small excess of carbonic acid ; the 

 determinations carried out with the two mixtures, are in good 

 agreement. When the figure is consulted the phenomena described 

 in the beginning of this paragraph will be clear. As long as gas is 

 present, the solid compound can only exist for pressures which are 

 higher than the three-phase line SL^G. Dittk's determinations, which 

 are indicated both in the figure and in the table by the symbol D, 

 appear to depart perceptibly from mine; only in the neighbourhood 

 of 0° do the observations agree fairly well. It makes the impression 

 that DiTTE has determined the points where solid substance is formed 

 on increase of pressure, and that the pressures have been found 

 much too high through the retardation of the transformation 

 L -[- G — > S, though DiTTE mentions that he observed the pressures 

 at which the generation of gas ceased. In this respect the phenomena 

 are again in perfect analogy with the system sulphuretted hydrogen- 

 water, where Cailletet and Boruet's observations present analogous 

 deviations with mine. ^) Ditte does not lay claim, however, to great 

 accuracy for his observations ; he states that his determinations give 



1) These Proc. 13. 833, fig. 2 and table on p. 834. (1910/11). 



