Douhlc Refraction in Liquids. 

 Table I. — Gum-Arabic in Water. 



487 





T. 



V. 



A\xlO l . 



^xW. 





21 



170 



2-80 



105 



1 g. in 100 c. c. j 



21 

 21 



266 

 45-0 



44S 



168 



II. 1 



0-5 g. in 100 c. c. J 



26 

 23 



233 

 42-5 



112 

 2-24 



48 

 52-7 



III. 1 

 0-25 g. in 100 c. c. J 



20 

 21 

 23 



1S-3 

 28-3 

 36-6 



1-54 

 2-52 



3-08 



84 

 89 

 84 



Solutions II. and III. were made by diluting number I. 

 In general these results confirm those of Umlauf. The 

 effect is proportional to the speed of rotation, but not 

 directly to the concentration. As will be seen, the effects 

 are largely dependent on the manner solutions are treated 

 and made. The principal source of error in these measure- 

 ments arises from a depolarizing effect. When the cylinders 

 begin to rotate both halves of the field become brighter, and 

 it is then impossible entirely to extinguish one half by rotating 

 the analyser. This depokmzation made it much more difficult 

 to obtain a match, and so materially increased the error in 

 reading. With a slow speed, this caused an error of about 

 5 per cent, in the setting of the analyser, which increased 

 with the greatest speeds to 20 per cent. With very great 

 velocity no accurate results were obtainable. Water was 

 then put into the chest and the cylinders rotated at high 

 speed, but the appearance of the field did not change. Air- 

 bubbles were allowed to mix with the water and then fine 

 particles of dust, but neither showed any effect. This diffused 

 light may therefore be due to structures in the solution itself, 

 comparable with the wave-length of light, which scatter the 

 incident waves. This effect also increases as the solutions 

 become stiffer at low temperatures and, in strong solutions, 

 hindered observation greatly. 



Gelatine. 



The solutions for the following observations were made by 

 dissolving pure gelatine over a water-bath. It was then 

 boiled and cooled, and when at the proper temperature used 

 at once. 



2 M 2 



