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



In all cases but IV. the nitric acid was purified by distillation from silver nitrate ; in 

 series III. and Ilia, the acid was added in a concentrated form, in the others it was 

 diluted and titrated. LEDUC found a diminution in the mass of the deposits of 

 2 parts in 10,000 when free acid was present. 



We conclude, therefore, that whilst the abnormally low values which are observed 

 from time to time can only be explained by the presence of acid, it may be very difficult 

 in practice to add nitric acid without at the same time introducing other impurities 

 which may more than counterbalance the effects produced by the acid itself. 



L. Effect of Heating Silver Nitrate. 



It has been shown above that the mere act of electrolysis does not cause any 

 increase in the electrochemical equivalent of a silver nitrate solution, and that in our 

 experiments no contamination appears to be produced by the changes which take 

 place at the anode. For a considerable time we were of opinion that atmospheric 

 contamination with sulphide might in some way produce an alteration in the electrical 

 behaviour of the solution, but finally we were unable to uphold this explanation of the 

 heavy deposits. We believe, however, that a clue to the origin of the abnormal 

 deposits may be found in the behaviour of the nitrate when heated, and, on the other 

 hand, in the action of the nitrate on the filter paper, to which we have referred above, 

 but which in our own experiments we have only been able to detect at high 

 temperatures. 



Very early in the course of the investigation we noticed that the fusion of the 

 nitrate caused an increase ill the weight of the deposit. A perfectly normal salt (H^) 

 was fused, dissolved in water, and its electrochemical equivalent was found to be 

 I'll 838 (24c), an increase of 1 part in 10,000. A second similar experiment with a 

 slightly acid salt (W t ) showed an increase in the electrochemical equivalent from 

 T11819 (mean of several) to Til 835 (25c), the latter value being again 1 part in 

 10,000 higher than the normal. It was further noticed that the mother-liquors which 

 gave such high deposits were all obtained from samples of nitrate which had been 

 fused or strongly heated at some stage of their treatment. 



In order to test the effect of heat alone on the nitrate a q\iantity of the purified 

 salt was heated to incipient fusion for several hours, and the greater part of the 

 nitrate was removed by crystallisation. The colourless mother-liquor was electrolysed, 

 and gave for the electrochemical equivalent the value of T11972 (88c). We therefore 

 feel justified in suggesting that whilst other causes (action of light, action of filter 

 paper, &c.) may contribute to the production of heavy deposits, the heating of the 

 nitrate appears to be one of the most effective ways of producing this effect. It is 

 possible that traces of hyponitrite may be formed both by the action of heat and by 

 the reducing action of filter paper, but we do not wish to commit ourselves to the 

 view that the hyponitrite is the only, or even the main, source of the disturbances 



