18 Transactions. 



Jena glass and dropped straight into the special collecting-flask. The water 

 so obtained kept very well, showing a slight improvement after storage: 

 in an atmosphere free from carbon-dioxide. 



Preparation of Electrodes, etc. 



After the electrodes were in place they were cleansed thoroughly with 

 chromic acid. They were then platinized in a solution of platinum-chloride 

 and lead-acetate, a four-volt current being passed for twelve minutes, 

 reversing every half-minute. To clean from the platinizing solution, they 

 were then used as cathode for twenty minutes in dilute sulphuric acicl, 

 and afterwards thoroughly washed with distilled water. A good miiform 

 coating of black was thus given, making the bridge-readings satisfactorily 

 clear and definite. 



The cell constant was determined in the ordinary way, using ^-^ 

 potassium-chloride solution as standard. (Here, as in the case of all 

 solutions, the glass conductivity-vessel was filled up to a fixed height, 

 sufficient to cover the electrodes half an inch or more.) .Several determina- 

 tions gave a mean value for the cell constant of 0-0833. 



Experimental. 



Altogether some six hundred readings were made, but of these only the 

 final ones will be noted in this paper, unless for some special reason others 

 leading up to them seem necessary. In making readings care was taken to 

 note time, temperature, and gauge-pressure, as well as the bridge-reading. 



Conductivities are expressed throughout in reciprocal ohms. 



In most cases it was thought sufficient to determine the conductivity 

 corresponding to every half-atmosphere pressure from 1 to 2i atmospheres, 

 and to every five atmospheres from 5 to 30 inclusive. 



Pressures are given as absolute values. 



Dial-gauge readings were obtainable to well within a tenth of an atmo- 

 sphere ; mercury-gauge readings to one five-hundredth of an atmosphere. 



Series I. 



Temperature constant = 18° C. (+ 0-05°) in thermostat ; stirrer work- 

 ing continuously ; cell immersed. 



As fluctuations about the mean temperature were very small, produc- 

 ing only negligible variations in conductivity, the temperature throughout 

 taken as 18° C. 



Allowance made for half the conductivity of the water in calculating 

 the conductivity of the solution ; this done throughout. Calculations made 

 as follows : If R denote the fixed resistance used, W the resistance of the 

 solutions, c the conductance (= r), C the specific conductance or conduc- 

 tivity, K the cell constant, x the bridge-reading : — 

 therefore R : R' = ic : 100 — x 



R ^iOU - X) 

 Kx 



and C = 



Jt (100 - X) 

 Work done with descending pressures. Air withdrawn through mercury- 

 gauge valve by a Fleuss pump. Valve then closed, and CO2" allowed to 

 fill the apparatus. This in turn withdrawn, and process repeated several 

 times till all air thus swept out. Pressure put up to 30 atmospheres. 



