( 696 ) 



Further, care has been taken to give the tangent plane the proper 

 inclination at these points in agreement with 



p := — ( — ) ^^ ^^ ( T ) ^^ ^^^'^^ temperature and pressure shall 



have their real value. 



On the given drawings (scale ^ /^ of model) for plan and elevation 

 PL III, fig. 3 and 6 — one side elevation has been rejected as it 

 does not clearly show the course of the pressure and temperature 

 line — the behaviour of the line 7'= const, ;9 = const, ?; = const, 

 t] = const and the position of the triple point can be seen without 

 further explanation. We draw attention to the intersection of the connodal 

 line Sa Sb bv the connodal line Sl S/j and further to the passage 

 of the isotherms over the connodal line and the crossing of the 

 isotherms with their corresponding isopiestics. In order to read from 

 the isotherms, given on the model, tiie corresponding values of /; 

 and V, the diagram of the isotherms (see PI. I, fig. 2) was constructed, 

 which reminds one of the course of the isotherms derived from the 

 VAN DER Waals' equation. The point Z^ in this figure corresponds 

 to the triple point for li(iui(l and llie two solid modifications of 

 carbon dioxide. According to Tammann the pressure is 2800 K.G. 

 The point KLSa is the critical point of the modification A in the fusion 

 line. According to the model the critical pressure would be 6500 K.G. 

 and the reduced temperature 1.7, 



The critical point GL occurs so far to the right on this scale 

 (the unit of volume is equal to that of PI. Ill fig. 5 and 6) that it 

 cannot be represented in the drawing. 



No critical point exists for the transition of Sb to L omving to 

 the interposition of the ridge Sa. The binodal line on Sb antl L, 

 loses its physical meaning at a given position of the rolling tangent 

 plane. A continuous passage from Sb to Sl is only possible through 

 the gaseous as an intermediate state. 



An important result can be obtained from the foregoing. Whenever 

 substances exist whose molecules undergo changes in the transition 

 to the solid state, which are mechanically similar to those which 

 determine the condition of the two phases, these said substances 

 Avill also agree with the law of corresponding states in the solid 

 condition. An experimental investigation for the continuity of the 

 solid and gaseous states would be best made on the substance with 

 the lowest critical pressure. If, for the moment, we assume that i/, and 

 CO, are sufficiently comparable from this point of view — at present 

 no better example is at hand — - the critical point solid-gas should 

 be sought at about 1800 atm. and — 210' C, and thus in possible 



