290 Miss E. M. Walton on Liquefaction and Cold 



Subtracting (20) from (21), we get 



= <fi-c)f±±-*r. ... . (24) 



Substituting from (23) in (24), we obtain 



c*- 4Rc 3 + 3RV + 2r(U + c) = 0. 

 Similarly we may obtain 



a ± + 2Ea 3 - { 6K?< + 3E 2 }a 2 - 8Km - 2RV = 0. 



By solving either of these equations for any particular case 

 the value of a or c may be obtained ; and then the values of the 

 other quantities may be easily got from equations (19), (20), 

 and (23). 



This case can only have interest when it is not practicable 

 to reduce the electrode resistance considerably below that of 

 the battery. 



XXXVI. Liquefaction and Cold produced by the mutual Reac- 

 tion of Solid Substances. By Miss Evelyn M. Walton*. 



THE mixing of two dry, finely-powdered salts, one or both 

 containing water of crystallization, is often attended by 

 liquefaction with decrease of temperature, which in many in- 

 stances is very marked; and sometimes there is also a decided 

 change in colour. 



A transparent homogeneous liquid is sometimes, though 

 rarely, obtained; but generally the liquid holds in suspension 

 an insoluble compound or an undissolved salt either in the 

 hydrous or anhydrous state: and sometimes the consistency is 

 that of a stiff paste. 



History. — It has long been known that freezing-mixtures 

 may be made by mixing some salt with ice or snow; and in 

 1875-6 G-uthrief determined the lowest attainable temperature 

 of quite a large number of such mixtures. He found that 

 the lowest temperature obtained with any given salt was the 

 same whatever its initial temperature; also that, within certain 

 wide limits, this was independent of the proportions used. 



The earliest allusion I find made to freezing-mixtures 

 formed by the use of salts only, is in the ninth volume \ of 

 Silliman's Journal, where Ordway, in a paper on Nitrates 

 mentions experiments in which the mixture of ammonium 

 bicarbonate with hydrated iron nitrate and with hydrated alu- 

 minum nitrate was followed by a reduction of temperature 



* From the ' American Journal of Science ' for September 1881. 

 t Phil. Mag. [4] xlix. p. 210. % H., ix. pp. 30, 31, 33, 



