84 



CONDUCTIVITY AND VISCOSITY OF SOLUTIONS 



31 



T 





fox 



of tubes (we used only two, figure 32) being filled with toluene, which 

 has about 6 times the cofficient of expansion of mercury. Instead of 

 using a 0.75 mm. capillary, into which a platinum wire connecting with 

 the regulating circuit was introduced, as in the old mercury regulator, 

 a capillary tubing of 2 mm. internal bore was employed, and the con- 

 tact was made by means of a steel wire of about 1.5 mm. diameter and 

 rounded at the end. The regulator worked with a fairly high degree 

 of accuracy, having a total variation of only 0.01 at 25 and lower 

 temperatures; and for a time it worked fairly well at 35, but it did not 

 prove to be satisfactory for any length of time at the latter temperature. 

 One difficulty was that the mercury at the surface of the glass sooner 

 or later became covered with toluene, and this began to creep out, 

 especially when the regulator was 

 not kept constantly at the desired 

 temperature, but was allowed to 

 cool down over night. 



This question in the meantime 

 suggested itself : Why is it not pos- 

 sible to have two or more long 

 tubes of thin glass containing mer- 

 cury instead of toluene, and in order 

 to avoid too great a weight, to have 

 these tubes of narrow bore? Thus, 

 we would have a greatly increased 

 surface of mercury, in comparison 

 with the old form of regulator, and 

 therefore a greater expansion. (See 

 figs. 33 and 34.) Such a form was 

 tried with great success. 



The supply of heat to the ther- 

 mostat was controlled by a gas- 

 regulator consisting of a 150-ohm relay, connected electrically with the 

 thermo-regulator and having an arrangement attached directly to the 

 armature, for cutting off the gas. 



CORRECTIONS FOR EXPANSION AND CONTRACTION. 



When the conductivities of electrolytes in water as a solvent are 

 determined at the temperatures at which we worked that is, 15, 

 25, and 35- when the solutions are made up at 20, the change in 

 volume caused by the expansion or contraction of the solvent and 

 solutions between 20 and these temperatures is so small that the 

 volume correction can be neglected. With alcohol and mixtures of 

 alcohol and water, however, this is not the case. The expansion here 

 is very appreciable, and there are, in consequence, changes in the 

 normality of the solutions for which corrections should be made. 



FIGS. 31, 32, 33, and 34. 



