532 PROCEEDINGS OF THE AMERICAN ACADEMY. 



equilibrium line which it has not been found possible to cross. At 

 four of the five triple points there are two such lines, and at the fifth, 

 I-II-III, the possibility of carrying II into the region of I was not 

 tried. At three of the five points water is one of the substances, so 

 that the statement is obviously true ; at the other two points the solid 

 II has the same relation to the solids above it that the solids above 

 have to the liquid above them. 



It was not found possible to extend any two of the curves so far 

 into a region of instability as to give a triple point between three un- 

 stable phases, nor was the third unstable curve starting from this un- 

 stable triple point ever found. This third curve would have no region 

 of stability whatever. The nearest approach to this was in the exten- 

 sions of the III-L and VI-L curves. No especial attempt was made to 

 realize such an unstable triple point, however, as it would have been a 

 matter of considerable difiiculty, but there seems no reason why such 

 a point should not be found. 



No such constancy was ever found in these subcooling experiments 

 as to suggest the necessity of the existence of the metastable limit, as 

 is claimed by many writers. With a particular piece of apparatus it 

 may be possible to obtain fairly consistent results, but when the appa- 

 ratus is being continually changed as it was here there seems to be no 

 obvious regularity. There is no reason why there should be, if the for- 

 mation of the nucleus of the new phase, which starts the reaction, is a 

 matter of chance as seems likely. Owing, however, to the fact that 

 there is at every triple point one equilibrium curve which it is not pos- 

 sible to cross, there are going to be lines reaching from every one of the 

 triple points limiting the existence of one or more of the phases, which 

 give the same impression as the metastable lines recently drawn by 

 Tammann in the neighborhood of the triple point I-III-L for water, 

 and also in the neighborhood of a triple point of phenol. ^^ 



In one respect the possible amount of subcooling showed great regu- 

 larity and is of sufficient significance to deserve special mention. This 

 is the fact, already noted, that a form is much more likely to appear 

 again if it has appeared recently before. This fact was of great con- 

 venience in obtaining the change of volume points, because here one 

 phase has to be allowed to be completely replaced by another, and the 

 first phase is then wanted again in obtaining the second AF point. 

 Very little difficulty was experienced in getting the desired form to ap- 

 pear under these circumstances. This was particularly true on the 

 V-VI and the V-L curves, the modification V being the hardest to 



" Tammann, ZS. Phys. Chem., 75, 75-80 (1910). 



