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IOWA ACADEMY OP SCIENCE 
sulphate was allowed to settle and the supernatant liquid de- 
canted. 
Copper Sulphate. The pure salt was further purified by re- 
crystallization. Clear stock crystals were carefully picked and 
dissolved in hot water. This solution was then filtered and al- 
lowed to crystallize. Clear crystals of about the size of a pea 
were picked and these were washed with distilled water. The 
saturated solution was preserved for preparing the cells. 
Amalgam. The copper amalgam was prepared electrolytically. 
For this purpose a standard solution of copper sulphate con- 
taining exactly 25 grams of copper per liter was prepared. To 
make an amalgam of any desired concentration, a given weight 
of the pure mercury was placed in the electrolyzing vessel and 
the number of cc containing the desired weight of copper was 
added from a burette. Sufficient water was added to give a 
workable solution volume. Contact with the mercury cathode 
was made by means of a small platinum wire sealed into the 
end of a narrow glass tube containing the mercury which made 
the contact with the copper wire terminal. In order to hasten 
the electrolytic deposition of the copper, the platinum spiral 
anode was rapidly rotated by means of a small electric motor. 
The current was allowed to pass until a few drops of the solu- 
tion tested with potassium ferrocyanide gave no indication of 
copper. After deposition the amalgam was quickly separated 
from the supernatant liquid by means of a stop-cock at the bot- 
tom of the electrolyzing vessel. 
Cells. Only cells of the ‘‘H-type” were used and these were 
specially constructed for immersion purposes. According to 
Wolff and Waters, the size and dimensions of the cell do not 
affect the electromotive force but they do affect the rapidity 
with which the cells assume the temperature equilibrium. 
The cells were made up in the usual. The amalgam and 
mercury were introduced into their respective limbs by means 
of pipettes, each to the depth ofi one and one-half centimeters. 
Upon the mercury was placed a two centimeter layer of a thick 
paste consisting of the mercury, mercurous sulphate and the 
saturated solution of copper sulphate. In each limb was next 
placed a two centimeter layer of clear picked copper sulphate 
crystals and the cell was, then nearly filled with the saturated 
