338 PRINCIPAL HENRY A. MIERS AND MISS FLORENCE ISAAC ON' THE 



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VI. The solubility curves for the different modifications of monochloracetic acid 364 



1. The a-solubility curve 366 



2. The /3-solubility curve 366 



3. The y-solubility curve 367 



VII. Relative positions of the a-, /?-, and y-solubility and supersolubility curves 367 



VIII. Additional experiments with pure monochloracetic acid 368 



PART II. MIXTURES OF NAPHTHALENE AND MONOCHLORACETIC ACID. 



Introduction 369 



I. The solubility curves 370 



1. Solubility of naphthalene in monochloracetic acid 371 



2. Solubility of the a-modification of monochloracetic acid in naphthalene .... 371 



3. Solubility of the /^-modification of monochloracetic acid in naphthalene . . . . 371 



4. Solubility of the y-modification of monochloracetic acid in naphthalene . . . . 372 



II. The supersolubility curves 372 



1. The naphthalene branch of the supersolubility curve 375 



2. The a-branch of the supersolubility curve 375 



3. The /J-branch of the supersolubility curve 375 



4. The y-branch of the supersolubility curve 376 



Discussion of results and conclusion 376 



Introduction. 



OUR previous papers on spontaneous crystallisation have dealt with the supersolubility 

 curves, firstly, of pure substances ; secondly, of mixtures of two or more substances 

 which do not form mixed crystals ; and, finally, with naphthalene and /8-naphthol ; 

 the last form mixed crystals of the type (l) of ROOZEBOOM, in which the freezing- 

 points of all mixtures lie between the freezing-points of the pure components. 



The object for which the present investigation was undertaken was to study the 

 spontaneous crystallisation of two substances which form mixed crystals and possess a 

 minimum or eutectic freezing-point. 



Monochloracetic acid and naphthalene, as described by CADY (' Journ. Phys. 

 Chem.,' 1899, 3, p. 127), seemed to supply convenient material for this purpose. For 

 monochloracetic acid melts at 62 C. and naphthalene at 79 0- 9, both these temperatures 

 lying within a range suitable for the methods which we had previously employed. 

 According to CADY, the mixture containing 2 9 '4 per cent, naphthalene and 70'6 per 

 cent, monochloracetic acid has a minimum melting-point of 53'5, and is, therefore, 

 the eutectic mixture. CADY also conducted a series of experiments which enabled 

 him to trace both the melting-point and the freezing-point curves in both sides of the 

 eutectic, and he found them to be separated by a considerable interval. These curves, 

 therefore, appear to have been well established, and we thought it would be ohly 

 necessary for us to trace the supersolubility curves and find their relation to the 

 curves determined by CADY. We began by attempting to verify his freezing-point 



