498 Mr. A. W. Warrington on 



weight for the latter, the difference in the elastic properties is 

 not so easily explained in that way. The diffusibility of cane- 

 sugar is to that of white of egg as 7 to 1. If these rates of 

 diffusion are representative of the general properties of the 

 two substances, we might expect to find a proportional double 

 diffraction in solutions of cane-sugar. A marked effect of 

 double refraction is found with 1 part of gelatine in 10,000 

 parts of solution. In a solution of cane-sugar containing 

 6000 parts in 10,000 no such effect could be found. 



Even in the most dilute solutions of gelatine there must be 

 a structure similar to that of solid jellies. When a small 

 stress is applied, a strain arises in this structure which renders 

 it double-refracting. When we go beyond the limit of elas- 

 ticity this structure breaks down ; and what we then have is 

 probably a secondary effect, caused by the parts of a substance 

 slipping over one another. It may be this secondary effect 

 which has been studied in researches on this subject. It is easy 

 to see how, after this breaking down reaches a maximum, the 

 double refraction should increase as the velocity of rotation 

 becomes greater, as is the case in the oils and in solutions of 

 non-gelatinizing colloids. We can also conceive of conditions 

 in which the amount of double refraction is not a function 

 of the speed, as was found to be true with 4 grains in a litre 

 at 27°. 



That the rotation should change sign remains yet unex- 

 plained, but that it does so when a sufficiently high speed is 

 reached cannot be doubted from the regularity with which it 

 appeared. 



My sincere thanks are due to Professor Brace, who has 

 directed this investigation. 



University of Nebraska, 

 May 1899. 



LVI. Hydrometers of Total Immersion. 

 By Arthur W. Warrington, M.Sc* 



T^HE principal inconvenience of weighing in water arises 

 from the fact that the fine suspension-thread is not 

 uniformly moistened ; the meniscus of the water changes its 

 form and deadens the oscillations of the balance very rapidly. 

 F. Kohlrausch (Ann. der Phys. und Chem. vol. lvi. p. 187) 

 finds that if the platinum suspension-wire be first covered 

 electrolytically with platinum-black and then heated for a 

 short time in a small bunsen-fiame until it turns grey, it 

 becomes uniformly and completely moistened when immersed 

 * Coram imicated by the Author, 



