208 REV. S. M. JOHNSTON 



PART III. 



Conductivity Observations at High Temperature. An Improved Method 



of obtaining these. 



Those who have given conductivity values at high temperatures, say, from 99° to 

 100° Centigrade, have done so only for dilute solutions, with perhaps the single exception 

 of NaCl, for which Lyle and Hosking * have given values up to a concentration of four 

 gramme equivalents per litre, and, speaking generally, observations have only been 

 made to a dilution of about one-thousandth normal. 



I resolved to test whether this dilution was satisfactory for the purpose of deter- 

 mining the conductivity at infinite dilution, and also to obtain conductivity data at 

 very much higher concentrations than those used by other observers, with an object in 

 view which will be apparent in Part IV. of this paper. 



To do so I designed two electrolytic cells, one for dilute, the other for concentrated 

 solutions, suitable for direct heating. The conductivity observations I have made 

 have been at a temperature near the boiling point of the solvent, with the conditions as 

 nearly as possible the same as those under which the observations of boiling-point 

 elevation were made. Rough sketches of the cells are given in figs. 6 and 7. 



Fig. 6 represents a section of the cell for dilute solutions, with a range, say, from 

 normal to one- or two-thousandths normal. B is the outer or boiling tube. The tube 

 D contains, when the apparatus is in use, a condensing tube of the Beckmann pattern. 

 C is an inner tube fitted into B by means of a rubber stopper F, through a hole which 

 it fits tightly. The electrodes E and the thermometer T reading to tenths from 97° 

 to 110° Centigrade, and having its scale entirely above A', are placed in the inner tube C. 

 This tube is perforated at a and a'. The one opening allowing the solution placed in 

 the boiling tube B to pass into or out of the inner tube, the other allowing the vapour 

 formed in C to pass over to the condensing tube D. The glass tubes b and b', by 

 means of which the cell is connected with the bridge, pass through a vulcanite top A', 

 in which they are cemented, and through a rubber stopper F' into the inner tube. The 

 thermometer does so also, but is not cemented into the vulcanite top. A little side 

 tube G was attached and fitted with a rubber stopper for increasing the concentration 

 of solutions by the direct addition of salt. 



The tube designed for strong solutions with which conductivities may be measured 

 from half-normal solutions to any degree of normality desired, is represented in fig. 7. 

 AA' is the boiling tube, which has two limbs, with short tubes D and D' attached to 

 hold small condensers of the Beckmann pattern. The tubes have each a short resistance 

 portion, as represented. E and E' are the electrodes not fitting tightly the tubes in 

 which they are placed. The glass connection tubes F and F' pass through rubber 

 stoppers C and C, and the vulcanite tops a and a', into which they are fixed by 



* Phil. Mag. (6), 3, 487, 1902. 



