W. B. B. Edwards — On the Separation of Minerals. 273 



rock would withdraw part of the heat from the hotter till an equality 

 of temperature was reached. But this is not what takes place ; the 

 subsiding rock does not come into contact with strata at a higher 

 temperature. 



So far from heat being withdrawn laterally and from below, the 

 general outflow of heat is checked in the areas where sediments are 

 being laid down. In these areas the sphere is losing less heat than 

 where the surface continues in a normal condition. A portion of 

 the heat that would otherwise escape into space is being used up in 

 heating the sediment. 



Mr. Davison seems to have had a glimmering of this truth before 

 completing his " Note," for the last paragraph but one is entirely 

 opposite and contradictory to the preceding which I have quoted. 



Unfortunately the effect has not been to compel him to withdraw 

 the erroneous view, but to attempt to minimize the dynamical effect 

 of the true one. Having dealt pretty freely with the quantitative 

 problems in my " Origin of Mountain Eanges," I do not propose to 

 enter upon this phase here. 



To say that the sediment piled up in an earth trough " loithdraws " 

 heat from the underlying strata is about as correct as to maintain 

 that covering a steam-boiler with felt withdraws heat from it. To 

 give an illustration ; if the valley of the Dead Sea were levelled up 

 with sediment, the underljang rocks would be raised to a tempera- 

 ture dependent upon the thickness of the sediment and its coefficient 

 of conductivity. The raising of the temperature of a body is not 

 usually considered to indicate a withdrawal of its heat. 



YIII. — On the Preparation op a Cheap Heavy Liquid, for the 

 Separation of Minerals. 



By W. B. D. Edwards, A.E.C.S., 

 of the Geological Survey of India. 



THE high price of all heavy liquids, and the consequent care that 

 has to be taken in using them, the latter of course entailing 

 great expenditure of time, were the reasons which caused me to make 

 experiments, with regard to the manufacture of Klein's solution 

 (borotungstate of cadmium) on a small scale. The price quoted in 

 a well-known chemical manufacturer's price-list is 3s. Qd. per oz. 

 My experiments have shown me that it can be made for about Id. per 

 oz., plus the value of the time of the maker. The process is very 

 simple, and not much time is necessary in making it. A rough 

 outline of the method of preparation is given by Dr. Klein in the 

 Comptes Eendus, vol. xciii. August, 1881. 



The apparatus required consists of two large porcelain evaporating 

 dishes 10' diameter, two of 6', and two of 3', two glass beakers 

 10' deep, and two 6' deep, a glass funnel and a water bath, A 

 fume cupboard or some arrangement for carrying off acid fumes 

 is also necessary. The following weights given will make 160 

 grains of cadmium borotungstate {i.e. about 50 c.c), and can be 

 conveniently manipulated in vessels of the size given above. 



DECADE III. — TOL. Till. — NO. "VI. 18 



