2lè THE ROYAL SOCIETY OF CANADA 



Ml-. R. L. McGregor undertook this part of the experiments. 

 Tlie measurements with the jet proved to be unexpectedly difficult, 

 and Mr. McGregor was compelled by illness to discontinue his work 

 before final re.sults were obtained. {Winter, 1912-1913). 



No. 28. R. T. Elworthy: — The critical angle of reflection from 

 solutions of surface active substances. The measurements of the critical 

 angle referi-ed to above were canied out l)y Mr. Elworthy, and al- 

 though the results are disappointing, in so far as they do not shed 

 much light on the problem for tiie solution of which thej^ were under- 

 taken, they are quite definite. Aqueous solutions of amyl alcohol, 

 phenol, aniline, and propionic acid were investigated. 



The measurements were made by observing, thi-ough a Nicol, 

 the image of a uniformly illuminated slot, about 2 cm. long, reflected 

 from the surface of the solution. The Nicol was held at the end of a 

 movable wooden arm, which was adjusted until the l^lack spot seemed 

 equidistant from the upper and lower end of the slot. In every case 

 the ci'itical angle gave a refractive index for the surface layer only 

 slightly different from that calculated (and determined by Pulfrich's 

 refractometer) for the body of the liquid. The slight deviation from 

 this value, was, it is true, in the direction to be expected from the 

 assumption of an accumulation of solute in the surface, but its magni- 

 tude suggests another interpretation of the results, viz: — that the 

 suj'face layei- is too thin to give the true value of the refractive index 

 from the critical angle of reflection. (Winter 1912-1913). 



No. 29. IF. J. Fawcett: — Rate of solution and crystallization of 

 gypsum. A crystal of gypsum was protected with wax so that only 

 3 cm.' of a freshly cleaved surface was exposed. This was rotated in 

 unsaturated and supersaturated solutions of gypsum, the concentration 

 of the liquid being determined at intervals by conductivity measure- 

 ments. The supei saturated solution was prepared by shaking a sol- 

 ution with finely ground gypsum and rapidly filtering through macer- 

 ated filter papci- until the liquid was almost opticafly empty. A strik- 

 ing difference was noted in the behaviour of the unsaturated and the 

 supersaturated solutions. In the foi-mer the concentration increased 

 rapidly, with deci-easing velocity, until the normally saturated solution 

 was pioduced. In the case of the supersaturated solution, on the other 

 hand, a comparatively rapid separation of gypsum appeared to take 

 place at first, followed by an almost stationary condition in which no 

 appi'ecial)le change in concentration occurred during a week's stirring, 

 although the solution was as much as 10% supersaturated. The 

 same phenomenon was observed with a solution 6% supersaturated. 

 In neither case could any change in the smoothness of the crystal be 

 detected with tiic microscope. Whether the stationary condition is 



