522 TRANSACTIONS OF SECTION B, 



6. The Crystallisation of Gold in the Solid State. 

 By G. T. Beilby, F.R.S. 



7. On the Temperature at which Water Freezes in Sealed Tubes. 

 By Professor H. A. Miers, F.R.S., and Miss F. Isaac. 



The authors showed in 1905 that in a cooling supersaturated solution, which is 

 kept stirred while a few crystals are growing in it, the refractive index rises until 

 at a certain temperature it attains a maximum value, and then suddenly falls ; at 

 this moment, also, profuse crystallisation takes place ; they concluded that this is 

 the temperature of spontaneous crystallisation. 



The conclusion is confirmed by the fact that the same solution enclosed in a 

 sealed tube begins to crystallise (in a shower) at precisely this temperature. 



The present paper describes similar experiments, sixty-eight in number, made 

 with water contained in sealed tubes which were vigorously and continuously 

 shaken by hand in a bath of brine. The temperature of the brine was reduced by 

 means of a tube coil through which the cold brine from a refrigerating machine 

 was pumped. The biine in the bath was kept thoroughly stirred by a horseshoe- 

 shaped wooden plunger perforated with holes. The rate of fall of temperature was 

 about 2° an hour. Temperatures were read by a thermometer divided to ^^ of a 

 degree. 



The water in the tubes was either tap-water, or ordinary distilled water, or 

 pure water of conductivity 1-1 x 10-". The initial temperature of the brine bath 

 varied from +9° to -2°. 



The glass used was both ordinary glass-tubing and hard Jena glass. Some of 

 the tubes were made up just before the experiment, some had been made up weeks 

 before. 



All the tubes froze between - 2° and - \°-Q ; the mean for all the experi- 

 ments being - 1°-86, and for the pure water - 1°-9. 



The ice generally appears at the bottom of the tube, grows very rapidly at first 

 in fan-like crystals, and then in a cloudy shower. 



The authors conclude that - 1°-9 is the temperature at which, under atmo- 

 spheric pressure, pure water freezes spontaneously, i e., in the absence of ice 

 particles. 



It is remarkable that this is also the temperature at which supercooled water 

 possesses its maximum refractive index according to Pulfrich. 



Friction produced by enclosing glass, or garnet, or galena, or lead in the tubes 

 with the water causes it to crystallise at a higher temperature, up to about -0°'4. 



PRIDAY, AUGUST 3. 

 The following Papers were read : — 



1. The Chemical Aspects of Cyanogenesis in Plants. 

 By Professor Wyndham Dunstan, F.R.S., and Dr. T. A. Henry. 



See Reports, p. 145. 



2. The Distribution of Frussic Acid in the Vegetable Kingdom. 

 By Dr. Greshoff. — See Reports, p. 138. 



