SPONTANEOUS CRYSTALLISATION OF MONOCHLORACETIC ACID, ETC. 377 



below their hypertectics ; these points were obtained in the usual way during the 

 course of the experiments. 



The curves of fig. 9 also show that in a mixture of two substances, one of which 

 exists in three modifications, eight freezing-points may be exhibited by a given 

 mixture as it cools. For example, the mixture of composition 15 per cent, 

 naphthalene 85 per cent, monochloracetic acid has yielded (i) crystals of the 

 a-modification of the acid by inoculation with a at 56 0- 5 ; (ii) crystals of the 

 /^-modification by inoculation with /8 at 50'5 ; (iii) a labile shower of a-crystals at 

 46'5 ; (iv) a labile shower of ^-crystals at 46 ; (v) crystals of the y-modification by 

 inoculation with y at 45'5 ; (vi) naphthalene crystals by inoculation at 43 0- 5 ; (vii) a 

 labile shower of naphthalene at 42 0- 5 ; and (viii) a labile shower of y-crystals at 39 0- 5. 

 Mixtures of other compositions exhibit multiple freezing-points in the same way. 



Further, the four solubility and four supersolubility curves of fig. 9 may be seen 

 to divide the whole diagram into twenty different regions, in each of which the 

 crystallisation of a mixture of naphthalene and monochloracetic acid may occur in a 

 different manner. For example, in the region bounded by DD, EE, GG, and HH, 

 , /3, or naphthalene may form by inoculation, or a inay form spontaneously, since in 

 this region any mixture is labile with respect to , metastable with respect to ft 

 and naphthalene, but unsaturated with respect to y. 



It must be mentioned that in these experiments on mixtures the monochloracetic 

 acid used was the commercial acid, and, although it was always dried for several days 

 in a desiccator, it almost certainly contains about 1 per cent, of water, so that the 

 results are slightly affected by this throughout. 



In conclusion, we may say that, although this research has not yielded information 

 concerning the crystallisation of a series of mixed crystals with minimum freezing- 

 point as we had at first hoped, it has shown the manner in which the crystallisation 

 of the different modifications of a substance occurs, when this substance is dissolved in 

 water or in some other substance which is not polymorphous, such as naphthalene ; and 

 it has also shown that each modification of a polymorphous substance possesses a 

 definite and different temperature of spontaneous crystallisation. This conclusion is 

 of some theoretical interest, for it suggests that in the cooling liquid one -modification 

 may come into existence after another and be ripe for crystallisation while still in the 

 liquid state. 



VOL. CCIX. A. 3 C 



