SPONTANEOUS CRYSTALLISATION OF MONOCHLOR ACETIC ACID, ETC. 359 



with higher concentration, such as from 98 to 100 per cent., it appears to bend round 

 and practically meet the y- solubility curve. For these higher concentrations it 

 therefore appears that the y-solutions hardly supersaturate at all. 



In the trough the shower of y-crystals grew quickly in sheets, adhering to the prism 

 and sides of the trough, thus making further readings for the index difficult. In only 

 a few instances was the stirring continued right through the experiment, for it was 

 generally found that when the stirring was constant throughout cooling, either an a- 

 or ^8-shower occurred, and not a y-shower. In experiment 42 the solution was not 

 stirred at all until after the y-shower had been obtained, and it will be seen from 

 fig. 7 that the index-temperature curve for this experiment consequently crosses the 

 y-supersolubility curve somewhat and passes into the labile state for y. 



IV. Motwchloracetic Acid (nearly pure] stirred in an open Beaker at Higher 



Temperatures. 



* 



In the above experiments the solutions containing from 98 per cent, to 100 per cent. 

 of the acid crystallise spontaneously at comparatively high temperatures, i.e. from 

 about 46 to 52'5 for the various modifications of the acid. 



Since it is not very convenient to work at and above these temperatures in the 

 goniometer trough owing to the fumes from the acid which attack the metal of the 

 goniometer slightly, a few additional experiments were undertaken in which the acid 

 was heated to between 70 and 80 and stirred in a small open beaker as it cooled. 

 The temperatures at which the various showers occurred were noted, and the stirring 

 was again effected by means of the small revolving platinum stirrer. 



The acid was taken direct from the bottle and no water was added. Previous 

 experiments on the refractive index show that the acid, unless carefully dried for 

 some days in a desiccator, nearly always contains from 1 per cent, to 1 '5 per cent, of 

 water, so that the concentration of the acid used may be regarded to be from 

 98 '5 per cent, to 99 per cent., unless previously dried, when it is probably about 

 9 9 - 5 per cent. The following results were obtained : 



1. a-shower. 



