THE DENSITY OF ZINC AMALGAMS. 



13 



The cadmium was electrolyzed from a strong acid solution of " chemically 

 pure " cadmic sulphate ; otherwise the procedure was similar to that described 

 for zinc. The weight of cadmium dissolved in one experiment was found 

 to be negligible for present purposes ; hence in succeeding experiments the 

 titration was omitted. 



The table of results follows : 



Nos. 1, 2, and 3 were made by dilution of amalgams of twice their re- 

 spective concentrations with an equal volume of mercury. 



The density curves are shown in figure 1. The dotted lines show the 

 average mixed density of the unamalgamated components calculated from 

 the following figures : 



Density of zinc = 7.04 



Density of cadmium = 8.55 

 Density of mercury = 1 3.545 



Consider, for example, the calculation of this quantity for a 3 per cent 

 amalgam of cadmium: 



One hundred grams of the mixture contain 3 grams of cadmium and 97 

 grams of mercury. 



.'. volume - 3 l 97 



-3- + 



8-55 ^ 



13-545 



Average density = Ioao 



7-512 



cc. = 7.512 cc. 



= I3-3I2- 



These dotted curves are very nearly straight lines ; from the portion of any 

 ordinate cut off between the upper and the lower curve for either metal, it 

 is easy to calculate the contraction which takes place during the formation 

 of the corresponding amalgam. Later these contractions will be discussed 

 in their relation to various energy changes occurring in amalgamation. 



Attention is now called to the method of using the undotted actual curves 

 in calculating concentration ratios. 



