SPONTANEOUS CRYSTALLISATION OP MONOCHLOKACETIC ACID, ETC. 369 



without the addition of water and yet the corresponding index-temperature curves on 

 the figs. 5, 6, 7 show the concentration to be between 98 and 99 per cent. 



Experiment 106. The same tubes of pure acid were used to determine the true 

 points of spontaneous crystallisation, with the following results. The tubes were 

 heated to 70 for various lengths of time to dissolve the crystals : 



a-showers, none. 



yS-showers in tubes containing corundum fragments occurred at 52, 52. 

 y-showers in tubes containing glass fragments occurred at 47'4, 47. 

 The tube containing the acid alone gave a y-shower at 46'5. 



The corresponding temperatures of spontaneous crystallisation for the three 

 modifications obtained above with the commercial acid were : 



a-showers at 52, 

 /3-showers at 50, 

 y-showers at 47. 



Here also, therefore, the results show that the commercial acid contains some water. 



Although no temperature of spontaneous crystallisation for a. was obtained with 

 the pure acid, it is probably above 52, just as the temperature of spontaneous 

 crystallisation for /3 with the pure acid was above 50. 



The above experiments with the tubes containing pure acid comprise over a dozen 

 different experiments, yet no a-showers were obtained ; this difficulty in obtaining 

 a-showers in sealed tubes has been noticed above. 



PART II. MIXTURES OP NAPHTHALENE AND MONOCHLORACETIC ACID. 



Introduction. 



The investigation of monochloracetic acid and its solutions in water being completed, 

 and the existence ascertained of the three different solubility and supersolubility 

 curves corresponding to the modifications a, ft, and y of the acid, we were able to 

 return to the study of the crystallisation of mixtures of naphthalene and mono- 

 chloracetic acid, which has already been referred to at the beginning of this paper, 

 It was there mentioned that in all probability mixtures of naphthalene and mono- 

 chloracetic acid do not form mixed crystals at all, but are only an example of the 

 crystallisation of two pure substances from their mixtures. In the long series of 

 experiments, of which the account is given below, there has never been any indication 

 of the formation of mixed crystals. A large number of mixtures were made up, 

 varying in concentration from 100 per cent, naphthalene per cent, monochloracetic 

 acid to per cent, naphthalene 100 per cent, monoohloracetic acid, and enclosed in 



VOL. ccix. A, 3 B 



