292 Dr. C. R. A. "Wright on the Determination of 



leading to the valuation 50130 gramme-degrees for the heat 

 developed during the precipitation of a gramme molecule of 

 copper by zinc, Thomsen used fluids containing altogether 800 

 molecules of water to one of zinc sulphate, &c. Hence, were 

 the acid used in the synthesis Zn, 0, S0 3 aq., to be H 2 S0 4 , 

 17 H 2 (corresponding nearly to the sp. gr. 1 - 175), instead 

 of H 2 S0 4 , 800 H 2 0, the heat-development would be greater 

 than 106090 by 17632-15986 = 1646 gramme-degrees per 

 gramme molecule (15986 being the heat of dilution of 

 sulphuric acid when n = 17, deduced from the above table): 

 this corresponds to 823 gramme-degrees per gramme equivalent 

 = •036 volt; i.e. the E.M.F. corresponding to the heat- 

 development during the displacement of copper from copper 

 sulphate, by zinc would be greater than 1*105 volt by *036, 

 or would be 1*141 volt. To this amount should also be 

 added the value of the E.M.F. equivalent to the heat-absorption 

 during the dilution of Zn S0 4 , 17 H 2 to Zn S0 4 , 800 H 2 0. 

 In a similar fashion it is calculable that to the value 1*105 

 should be added the amounts *023, *019, and *008 volt when 

 sulphuric acid of sp. gr. 1*090, 1*050, and 1*010 respectively 

 surrounds the zinc, giving the sums 1*128, 1*124, and 1*113 

 respectively. Hence, finally, the following tables of values 

 result : — 



Zinc surrounded by Zinc-sulphate solution. 



Electromotive force corre- 

 sponding to net chemical Electromotive force observed. 



Bright zinc opposed to bright*) -j.-ion 



copper J 



Bright zinc opposed to electro- \ -i .i -i ,* 



copper J 



Bright zinc opposed to amal-") -. , , _ 

 1*105 + .r, gamated copper . . . j 



where x is a small Amalgamated zinc opposed to") 1#12() 

 quantity varying with bright copper . . . . / 

 the phvsical'condition Amalgamated zinc opposed to ) 1 . 1U 

 of the copper depo- A electro-copper . . . . / 

 sited. Amalgamated zinc opposed to ),..„ 



amalgamated copper . . J 

 Electro-zinc opposed to bright ) .. 101 



copper |1MZ1 



Electro-zinc opposed to elec- 1 -. , TF . 



tro-copper J D 



Electro-zinc opposed to amal- 1 , , 1 . 

 gamated copper ... J 



action. 



