594 MR. F. E. SMITH, MR. T. MATHER, AND DR. T. M. LOWRY 



take place at the anode with formation of silver nitrite. It was therefore of interest 

 to determine the effect of this substance on the electrochemical equivalent. 



RICHARDS* prepared silver nitrite by boiling silver nitrate solution with finely 

 divided silver, and obtained with a nitrate solution saturated with it a value identical 

 within 1 part in 200,000 with that found with a pure nitrate solution. He also 

 prepared nitrite from pure potassium nitrite and silver nitrate and concluded, from 

 voltameter experiments made with a nitrate solution saturated with the salt so 

 prepared, that the nitrite caused an increase in the deposit of between 30 and 80 

 parts in 100,000. 



A first experiment, in which a solution of pure silver nitrate was saturated with 

 silver nitrite (purchased as pure) by making a saturated solution of the latter and 

 dissolving the requisite quantity of silver nitrate in it, gave T11832 (2id) as the 

 equivalent. That the solution was saturated with nitrite was evident from the 

 copious precipitate of this salt which resulted when the silver nitrate crystals were 

 dissolved in it. 



A second experiment, in which a 50 per cent, solution of silver nitrate was saturated 

 with nitrite by the addition of KNO 2 and then diluted and filtered, gave the value 

 1 '11 837 (52d) for the electrochemical equivalent. In this case the saturation of the 

 solution was evidenced by the fact that needles of silver nitrite actually crystallised 

 out from the solution on standing in a cool place. 



The above experiments show clearly that silver nitrite even when present in 

 considerable quantity does not raise the electrochemical equivalent by more than 

 one part in 10,000 and can only be an unimportant impurity. In view of the yellow 

 tint of the nitrite crystals, which should be colourless when pure, we are by no means 

 certain that the slight increase which we have observed may not be due to hyponitrite 

 (vide infra) and not to the nitrite itself. 



The influence of hyponitrite on the deposit does not appear to have been determined. 

 The salt was prepared by reducing sodium nitrite with sodium amalgam, neutralising 

 with acetic acid and precipitating with dilute silver nitrate solution. The yellow 

 precipitate of silver hyponitrite was drained on a filter, thoroughly washed with 

 water and shaken up with 120 grammes of a 50 per cent, solution of silver nitrate. 

 The strong saturated solution was then filtered and diluted to 400 cub. centims. with 

 water. A slight cloud was produced which was removed by filtration and the 

 solution was then electrolysed. The deposit was strongly striated and gave the value 

 1'11873 (88b). An earlier preparation gave a higher figure, 1'11930 (47c), but we do 

 not wish to lay stress on this. 



K. Influence of Acid*. 



It has been shown that there are a considerable number of impurities which raise 

 the electrochemical equivalent of a silver nitrate solution oxide, carbonate, chloride 



* RICHARDS and HEIMROD, ' Proc. Am. Ac.,' 37, p. 423, 1902. 



