[miller-kenrick] researches Ii\ PHYSICAL CHEMISTRY 219 



brought about by a change in the crystal or in the sokition has not 

 yet been definitely settled. Winter, 1912-13. 



No. 30. W. J. Fawcett:—The absence of supersaturation of 

 liquids in liquids. • In connection with the peculiar results found 

 for the rate of solution of gypsum (See No. 2D above) it was thought that 

 by investigating the rate of solution and precipitation in the case of a 

 solution of a liquid in a liquid, where the complicating factors of sol- 

 idity and crystal form were excluded, some explanation of the be- 

 haviour of gypsum might be reached. Here the unexpected difficulty 

 w^as encountered that even slightl}^ supersaturated solutions could 

 not be prepared. This fact is established by the following experi- 

 ments. 



A nearly saturated solution of one lic|uid in another w^as sealed 

 up in a tube of thin glass. This was clamped in a glass thermostat 

 parallel with a similar tube containing a slightly weaker solution to 

 serve as a blank for comparison. The apparatus was encased in a 

 black cloth, a beam of light being admitted through a slit in the side. 

 The tubes were observed endwise through two small holes in the front. 

 The temperature of the bath could .be changed or kept constant to 

 within 0-1° C. The temperatures at which turbidity appeared and 

 at which it vanished were compared for solutions of phenol in water, 

 valeric acid in water, aniline in water, chloroform in water with 

 alcohol, ether in water with alcohol. In every case the temperature 

 at which the turbidity disappeared was higher by one or two tenths 

 of a degree than the temperature of precipitation, but the difference 

 was of the order of magnitude of the experimental error, the slight 

 permanent opalescence observed in all liquids making accurate read- 

 ings difficult. Since it was thought that suspended particles might 

 act as nuclei for the precipitation of the liciuids, several methods were 

 tried for freeing the solutions of these suspensions. Neither filtering 

 through macerated filter paper nor repeated precipitation and re- 

 moval of the precipitated liquid, even when this was carried out with- 

 out exposure to the air, led to any increase in the tendency of the 

 liquids to form supersaturated solutions. {Winter, 1912-13.) 



No. 31. W. H. Martini: — The Tyndall effect in liquids. All liquids 

 show more or less opalescence when traversed by a bright beam of 

 light. Experiments were undertaken with a view to finding out to 

 what extent this opalescence could be removed b}^ various methods of 

 purification. The following methods were investigated: 



(a) Repeated distillation, in vacuo, in an all-glass apparatus, 

 without ebullition. Various kinds of glass were used. 



(b) Fractional distillation in vacuo, with the same precautions 

 as in (a). 



