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



sealed tubes and their melting- and freezing-points carefully determined. But in no 

 case was there found to be any appreciable difference in temperature between these 

 points, each mixture both melting and freezing at one definite temperature. CADY'S 

 results referred to above, p. 338, are, therefore, not confirmed by our experiments, for 

 although we have obtained a solubility curve for mixtures of naphthalene and mono- 

 chloracetic acid agreeing very approximately with the freezing-point curve obtained 

 by him, we have been able to obtain no evidence whatever of the existence of his 

 melting-point curve. 



We may assume, therefore, that mixed crystals are not formed from mixtures of 

 monochloracetic acid and naphthalene, and a study of the crystallisation of these 

 mixtures will, therefore, yield results similar to those already obtained for mixtures 

 of salol and betol ('Roy. Soc. Proc.,' A, 79, 1907), the only new feature being 

 introduced by the existence of the three modifications of monochloracetic acid. 



I. The Solubility Curves. 



In the experiments to determine the solubility curves for mixtures of mono- 

 chloracetic acid and naphthalene the mixtures of various concentration were weighed 

 carefully and enclosed in sealed glass tubes, the acid being dried in a desiccator for 

 several days before being used. 



The method of finding the freezing- or melting-point for each mixture was precisely 

 the same as that employed for the aqueous solutions, p. 3G4. Each tube was heated 

 in a water-bath until all the enclosed crystals had melted, with the exception of one 

 or two very small crystals at the top or bottom of the tube. The tubes were then 

 allowed to cool gradually in the water- bath and shaken continually while the enclosed 

 crystals were watched with a lens. The temperature at which the crystals began to 

 grow, as shown by their edges becoming sharp, was taken to be the freezing-point. 

 Similarly, with rising temperature, the point at which the few small crystals first 

 begin to lose their sharp outline is taken as the melting-point. In no case did the 

 freezing-point for any mixture vary by more than 0'5 from the melting-point, and 

 the mean of the two is taken as the true temperature of saturation. In a few cases 

 the mixture was placed in an open tube, which was firmly closed with a rubber 

 stopper, and the mixture was inoculated with a minute fragment of the crystal 

 required. The melting- and freezing-points were obtained in exactly the same way 

 by observing the behaviour of the small introduced crystal. Theoretically, each tube 

 may give four temperatures of saturation, according as the enclosed crystals are 

 naphthalene or either the a-, /3-, or y-modification of the acid, and practically all four 

 temperatures have been ascertained in more than one mixture. 



Each experiment was repeated several times, both with rising and falling tem- 

 peratures, and the following are the final results obtained : 



