112 Van X<inn and Huff— Hydrolysis and Electrical 



The lead sulphide was then filtered off, and the residua] 

 hydrogen sulphide was removed by a current of purified 

 air. During this process, which required several hours, 

 and thereafter until the conductivity measurements were 

 made, the receptacle containing the solution was kept in 

 a bath of ice and water. The solution of hypophosphoric 

 acid so obtained gave no test for hydrogen sulphide when 

 treated with acidified silver nitrate, and tests, by the 

 usual methods, for sulphuric acid, lead, and sodium were 

 negative. 



A sample of this solution was at once titrated with 

 sodium hydroxide, using Congo Red as indicator, and 

 with the result of this titration as a guide, was diluted 

 so as to be approximately N/32 with respect to H 4 P.,( )„. 

 Immediately after the completion of the conductivity 

 measurements described below, this solution was anal- 

 yzed iodometrically, both for hypophosphoric and phos- 

 phorous acids, by the method given in the preceding 

 paper, making each determination upon duplicate sam- 

 ples of the solution. The quantity of phosphorous acid 

 present was taken as a measure of the extent to which 

 hydrolysis had occurred. The amounts of hypophos- 

 phoric acid found in duplicate, 20 cm 3 samples were 

 0-05243 and 0-05257 grm., and of phosphorous acid in 

 samples of the same volume, 0-00050 and 0-00060 grm., 

 showing that the concentration of the H 4 P 2 6 , including 

 the small fraction hydrolyzed, was 0-03197 molar, and 

 that 98-96% of this amount was unhydrolyzed. 



The conductivity of this solution was measured as 

 soon as possible after its preparation, using a carefully 

 calibrated three-meter bridge and an accurate Leeds and 

 Northrup resistance box, and diluting the solution in the 

 conductivity cell in the usual way with the aid of accu- 

 rately paired pipettes. The cell constant was twice deter- 

 mined with solutions prepared from samples of specially 

 purified potassium chloride from different sources, both 

 determinations giving exactly the same value. The 

 whole series of dilutions was then repeated with a second 

 sample of the same solution, using a different pair of 

 pipettes, the duplicate results agreeing closely. The 

 conductivities recorded in the following tables are in 

 every case the mean of two such duplicate determinations. 



A 100 cm 3 portion of solution A was then hydrolyzed 

 completely by evaporating in a platinum dish over a 



