376 PRINCIPAL HENRY A. MIERS AND MISS FLORENCE ISAAC ON THE 



4. Tubes giving y-showers. 



Experi- 

 ment. 



Concentration of acid in the tube. 



Temperature of spontaneous crystallisation. 



172 

 173 

 174 



per cent. 



100 with glass fragments 



89-867 



85 '06 corundum fragments 



47 



42, 41 

 38, 39, 39-5 



Discussion of Results and Conclusion. 



It will be seen that in several experiments a single tube has given a shower of the 

 same crystals at several different temperatures, but the highest temperature obtained 

 is the real temperature of spontaneous crystallisation, and in the other cases the 

 mixture must have passed a little into the labile state for the modification in 

 question, either in consequence of insufficient shaking or too rapid cooling. In 

 plotting these results, therefore, on the temperature-concentration diagram of fig. 9 

 the highest temperature at which any mixture crystallised is taken to be the true 

 temperature of spontaneous crystallisation. 



Also, in plotting the supersolubility curve from the results of the experiments 

 giving a-showers, experiments 159 and 162 are disregarded, since they contain glass 

 fragments instead of corundum, and it was found that in tubes of almost exactly 

 the same composition containing corundum fragments (experiments 158 and 163) the 

 spontaneous crystallisation occurs at a considerably higher temperature. 



With these limitations experiments 144 to 174 will give the four branches of the 

 complete supersolubility curve for mixtures of naphthalene and monochloracetic acid. 

 They appear on fig. 9 together with the corresponding solubility curves. They are 

 fairly continuous curves, each running approximately parallel to the solubility curve 

 with which it corresponds. The two a-curves are separated by an interval of between 

 9 and 10 of temperature, the two /3-curves by an interval of about 5, and the two 

 y-curves by between 3 and 5, while the two naphthalene curves are separated by 

 between 2 and 3. The three branches of the supersolubility curve for monochlor- 

 acetic acid meet the naphthalene supersolubility curve in three points, thus giving 

 three hypertectic points at their intersections, just as three eutectics are given by 

 the solubility curves. These points occur at (i) 46 with composition 23 per cent, 

 naphthalene 77 per cent, acid, for naphthalene and the a-modification of the acid ; 

 (ii) 45 with composition 121 '5 per cent, naphthalene 78 - 5 per cent, acid, for 

 naphthalene and the /3-modification of the acid; and (iii) 41'3 with composition 

 11 per cent, naphthalene 89 per cent, acid, for naphthalene and the y-modifi cation of 

 the acid. 



It may also be seen that the ft- and y-supersolubility curves even cross the 

 naphthalene supersolubility curve a little, thus yielding spontaneous crystallisation 



