ON THE SILVER VOLTAMKTF.K 583 



III. The strongly acid mother-liquors from II. were evaporated on the water-bath 

 and dried in the oven until free from acid. The dry salt was further lu-.itcd until thr 

 hlue colour of the copper nitrate had disappeared, and was then dissolved in water, 

 filtered, and recrystallised until colourless. After one further crystallisation a 

 solution was prepared as before, and the electrochemical equivalent determined. 

 Three determinations gave the values 



III. 1-11827 (266) 

 1-11830 (27 d) 

 1-11827 (29a) 



Mean 1*11828 milligrammes per coulomb. 

 Other samples of recovered silver nitrate purified by this method gave the values 



IV. 1-11826 (28c) 

 V. 1-11831 (356) 



1-11827 (35c) 



VI. 1-11816 (?) (44c) 



1-11830 (46c) 



VII. 1-11830 (656) 



whilst a 50 per cent, solution prepared by dissolving recovered silver nitrate (purified 

 as above) in its own weight of water gave the value 



VIII. 1-11827 (306). 



IV. Silver Nitrate from Commercial Samples. As a further test of the possibility 

 of preparing silver nitrate of constant properties, two commercial samples were 

 procured, one from an English and one from a German firm, and these were purified 

 by recrystallising two or three times from water. One of these samples was of 

 especial interest, as it gave initially a lower value for the electrochemical equiva- 

 lent than any of the samples I. to VIII. which we had purified for ourselves, and 

 we were uncertain at first whether a higher standard of purity might not perhaps 

 be attained by a works-recrystallisation on a large scale than when smaller quantities 

 were dealt with. The recrystallised samples gave, however, entirely normal values, 

 and the low value of one of the commercial samples was therefore due to an 

 impurity which could be removed by recrystallising (see later p. 595). The values 

 obtained for the electrochemical equivalent were : 



