606 The Earl of Berkeley and Dr. C. V. Burton on 



Multiplying by c 1 and subtracting the complementary 

 -equation (multiplied by c 2 ) we get * 



cisi^~ — c 2 s 2 —J= — Cl v ^— + c 2 z ^-. . (22) 

 *c 2 ^c i 9c 2 dci y 



By assuming Boyle's law, the right-hand member of (22) 

 reduces to Margule's equation 



d log irjd log c 2 = d log <£/d log c x . 



This equation was experimentally verified by Zawidski t* 

 and consequently (18) is also experimentally verified. 



Concentration of a solution by centrifugalization. 



It is evident that the exact equation (15) 



dc 2 _ c 2 .~dw /~dc 2 

 d<Jr s±w . tlPj/Scg ' 



■can be applied to cases other than that of a stationary mass 

 of solution under gravity ; for instance, in the case of a vessel 

 containing a solution and whirled at a uniform rate round a 

 vertical axis the equation becomes J 



dc 2 _ c 2 'dio/'dc2 ■ . 



dC SiMfcPj/ttCs [ } 



where G is the potential of the " centrifugal force." 



So far as we know, the only experimental work on this 

 method of stratifying a solution, is that of van Caicar and 

 de Bruyn §, but their results, as calculated from the data 

 they give and other known quantities, seem incompatible 

 with (23). 



As an example take the following experiment recorded by 

 these authors : — 



A drum, 6 cm. in radius, was filled with a 12 per cent, 

 -solution of cane-sugar, which gave a rotation of 46°*8 in a 

 polariscope. The drum was rotated about its vertical axis at 

 a uniform rate of 40 revolutions a second for four hours. 

 Without stopping the apparatus, samples were then taken in 

 four capsules placed at different distances from the axis and 

 were tested in the polariscope. Sample 1 (central) was 



* Note that 0,^=6,1^ 

 t Loc. cit. dc '2 " O c i 



X Neglecting the effect of gravity on the horizontally rotating liquid. 

 % Bee. Trav. Chem. Leiden, vol/xxiii. pp. 218-223. 



