[MCINTOSH] SUPERSATURATED SOLUTIONS 271 



In the second method the supersaturated solutions were covered 

 with a sterilized layer of oil. Unfiltered air was bubbled slowly and 

 carefully through the upper part of the oil, so that the lower layer 

 was not disturbed. The solutions were then allowed to stand until 

 crystallization took place. Stokes' Law holds exactly for liquids, and 

 numbers from 10^^ to 10"" were found. I do not regard these 

 results with any confidence, and a method now being studied, where 

 minute particles are got in suspension by shaking, and the larger 

 particles removed by centrifuging would seem to lead to better figures. 



Salol 



Salol melts at 49°, and when properly sterilized remains liquid 

 indefinitely at room temperatures. When cooled to about —5° the 

 solution crystallizes spontaneously, or on the slightest shock. I have, 

 however, on a number of occasions cooled the liquid to — 80°, when it 

 appeared as a horn-like solid. 



On warming to room temperature, the salol in some of the tubes 

 still remained liquid; but in many cases was exceedingly sensitive to 

 shock. I may point out again here that simple heating to a few 

 degrees above the melting point is unlikely to give stable solutions. 

 They must be properly "sterilized." 



One gram of salol was taken and dissolved in 100 cc. of alcohol. 

 A portion taken out on a platinized platinum wire and allowed to dry 

 always induced crystallization (Mass =10'^ gni.). One cubic centi- 

 meter of the solution was made up to 100 cc. with alcohol. On apply- 

 ing the same inoculation method, crystallization was induced in about 

 20 per cent of the experiments. 



One cc. of the 10- solution was then added to 100 cc. of water. 

 The salol separated, and gave a milky liquid. A pipette delivering a 

 drop of 10 milligrams was made, and a single drop was allowed to fall 

 into the super-cooled salol. The surface tension of the latter kept 

 the drop beneath its surface and in a moment or two crystallization 

 began, often from 5 or 6 different points on the drop. This is quite a 

 pretty experiment, and the fact that the salol particles can penetrate 

 the skin between the water and salol is worth study. A drop 

 was then put on a microscopic slide, divided into sections and the 

 number of crystals counted. Ten milligrams contained about 1000;so 

 the mass of the particle was about 10'^, a result approximating 

 that obtained by Ostwald. 



The solution was then placed in a long tube, and the particles 

 allowed to settle. From time to time a small amount was pipetted 

 off, the diameter of the particles measured by a microscope, and the 



