490 



Mr. B. V. Hill on Accidental 



of 24 revolutions per second, and "000141 X for 39 revolu- 

 tions per second. The ratios of the retardation to the speed 

 were 36xl0 -7 and 41 x 10~ 7 . These results agree with 

 those of Umlauf at this temperature. 



Concentration. 



Solutions to be compared must be prepared in the same 

 manner. They must also be examined under conditions 

 similar in respect to speed. While the curves representing 

 this relation are of the same general character they cannot 

 be made to coiucide. Thus no comparison exists between 

 solution IV., containing four grams to the litre, and solution 

 VI., which holds one gram to the litre. At 27° the retarda- 

 tion is independent of the speed for solutions below a certain 

 concentration. In a solution containing 20 grams in a litre 

 the effect is not independent of the speed, and it will be seen 

 that the result in this case does not accord with the others. 



Table IV. 



g. in a litre. 



V. 



AX X 10 4 . 



-^ X10». 



cone. 



3-0 



466 



1-600 



T33 



4-0 



25-0 



2-112 



502 



5-0 



35-0 



3-080 



616 



6-0 



42-5 



3-220 



540 



7'5 



425 



4-256 



567 



10 



300 



5-208 



521 



200 



7-5 



7-840 



392 



These results show that, in solution of gelatine, under the 

 same conditions, the double refraction is proportional to the 

 concentration. This fact seems to be allied to Mauer's* 

 statement that the elasticity of jelly is proportional to its 

 concentration. 



The effect of temperature and time on the amount of double 

 refraction in a liquid is of importance, but is difficult to study 

 with the present apparatus. The temperature will remain 

 constant for a long time, but there is no satisfactory way of 

 regulating it. The magnitude of the double refraction also 

 depends upon the length of time the solution has been allowed 

 to stand. This effect of time depends in turn upon the 

 temperature, which makes the combined effect complicated. 

 * Wied. Ann. xxviii. p. 628. 



