350 



PEINCIPAL HENRY A. MIERS AND MISS FLORENCE ISAAC ON THE 



which in a solution of approximately the same concentration a shower of )8-crystals 

 appeared at 25, and the maximum index attained was 1 '436034 at that temperature. 

 It therefore appears that the supersolubility curve for y on the diagram lies to the 

 left of that for /3, just as the supersolubility curve for /3 lies to the left of that for ; 

 this is confirmed by all further experiments giving a y-shower. 



In another solution (experiment 37) which gave a y-shower the concentration was 

 approximately 97 '2 per cent. This solution was also examined in the trough of the 

 large goniometer, and it was at first unstirred and allowed to cool at rest until it had 

 passed the labile temperature for the a- and /3-modifications. The index rose from 

 1-430178 at 60 to 1 "440742 at 34'5. Stirring was started at 35, and after a few 

 minutes a labile shower of the characteristic y-crystals occurred at 34, the temperature 

 rising to 42 at once. No further readings for the index were possible owing to the 

 density of the shower, but the temperature was constant at 42 for 5 minutes after 

 the shower occurred. Then suddenly a transformation to /8 took place and a rise of 

 temperature to 48, after which again the temperature was steady for a considerable 

 time. The solution was then inoculated with a minute trace of the a-modification, 

 which caused an immediate transformation from /3 to a, and a new rise of temperature 

 from 48 to 52 -5. 



The three halts in the change of temperature in this experiment, namely, at 42, 

 48, 52'5, are probably at points where the index-temperature curves reach the 

 solubility curves for y, /3, and a respectively, though it was not possible to prove this 

 by a reading for the index at these temperatures. 



The above method was often found successful in obtaining y-showers, namely, to 

 cool the solution, without stirring, past the labile temperature for the a- and 

 /3-modifications, and then to start stirring as the solution continues to cool below 

 these temperatures. Sometimes the stirring causes an a- or /3-shower to come down 

 at once, but often the solution continues to cool without crystals appearing until the 

 labile temperature for y is reached, when a labile shower of y-crystals occurs, thus 

 determining a point on the y-supersolubility curve. 



The following are the results of a large series of experiments on solutions of various 

 concentrations : 



I. Solutions first giving a Spontaneous Shower of a-crystals. 

 (The solutions were stirred by means of the revolving platinum vane.) 



Remarks. 



The acid was dried in a desiccator before using. It was placed in the trough of the 

 large goniometer, the trough being first heated to about 40. The index rose 

 from 1-430774 at 66 to 1-436331 at 52. At 52 a dense spontaneous shower 

 of a-crystals occurred, the temperature rose to 61, and the whole mass became 

 solid. 



