12 



ENERGY CHANGES INVOLVED IN DILUTION OF AMALGAMS. 



and weighed at once. Since it was hard to adjust the amalgam to the 

 mark as described above, the length of the surplus mercury column was care- 

 fully measured, at times, and a correction applied to the observed weight. 

 (One centimeter of mercury in the tube weighs 0.200 gram, the mean of two 

 determinations.) Corrected data are given without comment in the table 

 at the bottom of page 1 1 . 



The record of a typical determination follows : 



(1) Weighing bottle -f- zinc 9.8685 



(2) Weighing bottle -j- zinc 9.1822 



Weight of zinc 0.686 



K 4 Fe(CN) 6 solution used = 1.85 cc. Therefore, 0.006 gram of zinc was 

 dissolved by sulphuric acid, and must be subtracted. 



Weight zinc in amalgam 0.680 gram 



Weight mercury in amalgam 82.12 gram 



82.80 



Per cent zinc in amalgam = ? X 100 = 0.821 (t = 20 ). 



to 82.80 v J 



Weight of pycnometer and amalgam 74.685 to mark 1. 

 Weight of pycnometer 7-135 



67.550 to mark 1. 

 The absolute density of mercury at 20 is 13.545. 35 

 .". the density of the amalgam is 



&|5? X 13-545 = I3-472+ 



The table of results follows. In the last three calculations the assump- 

 tion is made that the coefficients of expansion of mercury and amalgam 

 over 4 are sensibly the same. 



Densities of Zinc Amalgams. 



From these figures a curve can be constructed giving the density of any 

 zinc amalgam between 0.821 per cent and pure mercury; some extrapolation 

 would probably be safe also. 



85 Ostwald-Luther, Hand- und Hiilfsbuch, p. 129. 



