MIXTURES OF ELECTROLYTES.—McINTOSH. 123 
Temperature. 
As the laboratory temperature varied considerably from day 
to day, the electrolytic cell was placed in a bath whose tempera- 
ture was regulated by a thermostat of the kind described by 
Ostwald in his Physico-chemical Measurenients, p. 59. The 
resistances measured were so small that a sharp “ minimum ” was 
obtained when a water bath was used. There was no necessity 
therefore, for a petroleum bath. The bath was stirred by a 
current of air from a small suction pump, and the temperature 
kept as near to 18°C as possible. When this temperature could 
not be exactly obtained, measurements of resistance were made 
at several near temperatures, and the temperature co-efficients 
found. The co-efficient was always about 2 per cent. per degree. 
The thermometer used was graduated to 0.1 degree centri- 
grade, and could be easily read to 0.05 degree. This meant a 
possible error of 0.1 per cent. in the determination of the 
resistance. The errors of the thermometer had recently been 
determined at the Physikalisch-Technische Reichsanstalt, Berlin. 
The Platinizing of the Electrodes. 
The electrodes after having been boiled in alkali and acid, 
were placed 1 a very dilute solution of chloroplatinic acid 
(H, Pt Cl, ) and connected with a small battery, the direction of 
the current being frequently changed. When the electrodes had 
become covered with a black velvety coating, they were removed 
from the cell, and in order to get rid of the chloroplatinie acid 
which adheres strongly to the platinum black, they were washed 
several times with boiling water. On one occasion, in the course 
of the experiments, the minimum point was found to be indistinet. 
The plates were accordingly replatinized and distinctness found 
to have been regained. The experiments previously made (those 
on potassium chloride) may have been affected by a shght error 
due to defective platinizing. 
The Salts and Acids. 
The potassium and sodium chlorides, obtained as chemically 
pure from Eimer and Amend of New York, were further purified 
