( 229 ) 



3°. with no other equation of state suitable for a calculation we can 

 reach such a low temperature ; 



4". VAN DER Waals, for similar circumstances as are found on 

 this surface, has also derived analytically the particularities in the 

 coexistence-phenomena (Contin. II, p. 146, sqq.), and the agreement 

 between these results and the obser\ations of carbon dioxide and 

 methylchloride, found partly already by Hartman at + 9.'^5 C, will 

 probabl}^ appear even more clearly at — 25° C, 



5°. finally that a paper on an experimental determination of these 

 conditions of coexistence, which also van der Waals thinks very 

 desirable (Contin. 11, p. 154) will, as we hope, soon be published. 



The numerical agreement becomes less accurate because methyl-chlo- 

 ride is not similar to ether, with which substance the empirical reduced 

 equation of state for the reduced temperature of the methylchloi'ide 

 on this tf>surface is made to agree whereas this is the case with carbon 

 dioxide at the reduced temperature, which it has on this ip-surface. An 

 empirical reduced equation of state in good harmony for the reduced 

 temperature of 0.6 with methylchloride of — 25° C, for the reduced 

 temperature of 0.8 with carbon dioxide of — 25" C, would have 

 been more favourable for the obtainment of a numerical agreement. 



The plaster model obtained is represented on the annexed plate 

 fig. 1, it is 0,7 m. long (v-axis), 0.4 m. high (ifvaxis), 0,3 ra. broad 

 (.t'-axis). The large dimension in length was made necessary by the 

 great difference in density of the vapour phase between carbon dioxide 

 and methylchloride. 



The binodal curve and the tangents which connect two coexisting 

 phases, the nodal lines, are found by rolling a piece of plate-glass. 

 Fig. 2 shows the binodal curve with nodal lines, and also sections 

 V = const, projected on the .I'lfvplane, fig. 3 the same on the .ajv-plane; 

 fig. 4 shows the values of the pressure as function of the composi- 

 tion of the coexisting phases. 



It is obvious that: 



1°. the liquid ridge, i.e. that part of the surface which lies on 

 the side of the small volumes, when the dimensions of the surface 

 are not taken extraordinarily large, becomes very thin and the con- 

 struction is practically possible only if we take for it a plate of 

 uniform thickness (for instance a sheet of tin); 



2". while the tangent plane is rolled over the ridge of the liquid 

 part and over the convex vapour surface, as the ridge near the pure 

 methylchloride rapidly changes its direction, the point of contact 

 moves a long way on the vapour branch of the binodal line, 

 while the node on the liquid branch moves only a little. Hence in 



