ip4 Conductivity of Aqueous Solutions. Part VII. 



For the purpose of merely testing solutions at 18, when it was not 

 desired to make a measurement at higher temperatures, a small glass 

 conductivity-cell was used, such as is represented in figure 19, Part IX. 

 This had a capacity of about 40 c.cm., and was in the form of an ordinary 

 pipette ; the upper tube was provided with a stopcock, the platinum elec- 

 trodes were sealed in vertically through the shoulder of the bulb on 

 opposite sides of the upper tube, connection being made through glass 

 tubes containing mercury, and the lower exit tube was turned upwards, so 

 as to rise above the liquid in the temperature bath. Solutions could be 

 forced into this cell without any danger of contamination from the air. 



The resistance of the solution in the bomb was measured by means 

 of the usual arrangement, consisting of a new Kohlrausch three-meter 

 cylindrical slide-wire bridge (Hartmann and Braun No. 283), a small 

 induction coil, and a telephone connected between the ends of the slide- 

 wire. A switch was arranged to commutate the current from the coil, 

 and another to connect the bridge with the lower or the upper electrode. 

 The leads were of heavy copper wire, connecting with the bridge or with 

 the leads coming out of the temperature bath by means of double flexible 

 lampcord and flat binding-screws. 



The rotating carriage in which the bomb was mounted, as well as the 

 larger temperature baths required by this rotating arrangement, were simi- 

 lar to those used by Noyes and Melcher (section 28, Part III). Xyene was 

 used in the 18 bath, and naphthalene in the 218 vapor bath. A Beck- 

 mann thermometer was used in each. In the 306 bath benzophenone was 

 employed. Diphenylamine, boiling at 302, was used at first, and some 

 of the data on ammonium hydroxide were obtained at this temperature ; 

 but after a few experiments much of the substance had decomposed, and 

 the boiling-point rose and became uncertain. It was found impracticable 

 to use a Beckmann thermometer at this temperature, because its readings 

 were variable and not reproducible. A 360 Alvergniat thermometer, 

 graduated in degrees, was therefore employed. 



*This bomb was used until June 5, 1906, when the lining of it cracked; after this 

 date another bomb (No. 3) was employed. The first trouble from leakage occurred 

 in February, 1905, after the bomb had been in use for one month, when the lower 

 lining cracked near the bottom ; this was repaired by removing the lining and flow- 

 ing gold over the crack. No more difficulty was experienced, except from occasional 

 accidental leakage at the electrodes or the valve, until after the first heating to 302, 

 when a slow leak developed through a tear in the lining of the upper chamber, 

 caused probably by unequal expansion of the steel and the platinum lining. The 

 leak was so slow at first, however, that the conductivity of the ammonium hydroxide 

 solution could be determined at a given time, and the bomb then removed and 

 cooled without further loss, the solution from the bomb being always analyzed after 

 each heating, whether there had been leakage or not. After some attempts to locate 

 and repair this leak, the upper lining was removed and a new one put in (March, 

 1906). The bomb then held until June 5, when the lower lining again cracked. 



