SPONTANEOUS CRYSTALLISATION OF MONOCHLOEACETIC ACID, ETC. 367 



3. Points on the y-solubility Curve. 



The only points obtained by PICKERING on the y-solubility curve are 100 per cent, 

 solution saturated at 50, and 96 '02 per cent, solution saturated at 41'4. It may be 

 seen that both these points agree fairly well with the above results. 



The above points are found to lie on a continuous curve and give the y-solubility 

 curve which appears on figs. 7 and 8. The y-solubility curve runs nearly parallel to 

 the y-supersolubility curve, and is separated from it by about 7 of temperature, 

 except at the upper end, where the y-solubility and supersolubility curves approach 

 each other much more nearly. 



Nothing has been found to correspond to PJCKKKING'S solubility curve for 8. 



VII. Relative Positions of the a-, ft-, and y-solubility and Supersolubility Curves. 



In fig. 8 are plotted all the six curves obtained in this paper, namely, the three 

 solubility and three supersolubility curves for the a.-, ft-, and y-modifications of 

 monochloracetic acid, as well as a seventh curve formed by the outlying points 

 referred to above in this paper. It will be seen from the relative positions of these 

 curves that after a y-shower has occurred at the y-supersolubility curve and the 

 concentration of the solution has fallen to the y-solubility curve and it has become 

 just saturated with respect to y, the solution is always not only supersaturated, but 

 labile, with respect to a and ft. Hence only a slight stirring is enough to cause a 

 transformation of y into ft or a. without inoculation, and since the ^-supersolubility 

 curve is only separated from the y-solubility curve by from 1 to 2 C> 5 of temperature, 

 the y-crystals usually transform to ft when agitated. 



On the other hand, of the /8-curves the supersolubility curve lies to the left, and 

 the solubility curve to the right, of the a-supersolubility curve. Hence, after a 

 spontaneous shower of ft has occurred and the concentration has fallen to the 

 /3-solubility curve and the solution has become just saturated with respect to ft, it is 

 only metastable with respect to a, and not labile. 



Hence, unless the solution is inoculated with a, the /3-crystals are stable, as has, 



