304 REPORT— 1898. 



than is the case with cold solutions, it is much more convenient to employ 

 the latter. 



The time stated is sufficient for all ordinary quantities of metal under 

 the otlier conditions given. For small quantities it may be curtailed 

 somewhat, but it is preferable rather to reduce the current and the pro- 

 portion of ammonia. Even when the quantity of metal is considerable, 

 the great bulk of it is deposited in a relatively short time, and it is the 

 removal of the last portions which prolongs the duration of the ex- 

 periment. 



In connection with the electrolysis of nickel sulphate solutions, the 

 formation of nickel sulphide has sometimes been noted, becoming evident 

 Avhen the deposit is dissolved in dilute hydrochloric acid, as a slight black 

 insoluble residue. Though this was observed in several experiments, it 

 was not possible to fix the particular conditions which determine it. 

 Apparently it is not formed to any appreciable extent under the general 

 working conditions specified above. 



Where it is possible to select the quantity of metal to be used in a 

 determination 0'15 to 0-2 grme. will be found to be very convenient. For 

 many purposes, however, the quantity available may be much less than 

 that. In dealing with small quantities there is no need to employ the 

 ordinary large electrolytic basins unless a large volume of solution cannot 

 well be avoided. Very good determinations can be carried out in ordinary 

 platinum crucibles. In that case the quantity of ammonium sulphate 

 and of ammonia should bear the same proportion to the volume of the 

 solution as when the ordinary apparatus is employed. With a crucible 

 holding about 20 c.c. of solution that would mean barely one graipme of 

 ammonia and of ammonium sulphate, while the current to correspond 

 would be about 0-15 ampere. It has been found that in this way deposi- 

 tion is more rapid than when working with a large volume of solution 

 containing the same quantities of metal and ammonia, and with the same 

 actual current (oiot same current density). When working on a small 

 scale with small quantities of metal, there is, of course, less liability to 

 accidental errors, owing to the more compact nature of the deposit, and 

 the greatly diminished size of the vessel to be handled. 



Numei'ous experiments have been carried out in order to determine 

 the influence which may be exerted by other substances present in the 

 solution during electrolysis ; partly to discover if any are decidedly 

 beneficial, but chiefly to find out those which are distinctly objectionable. 



Potassium or sodium sulphate cannot be employed in place of the 

 ammonium salt without very considerably lowering the character of the 

 resulting deposits ; they ai'e invariably dark and rough, but with care the 

 numerical results are hardly, if at all, affected. The presence of these 

 salts, however, is not of itself harmful, for perfectly good deposits can be 

 obtained by employing ammonium sulphate along with them in the usual 

 manner. 



Until recently it was quite generally stated that the presence o/ chlorides 

 in the solution was objectionable, but this has been contradicted by 

 F. Oettel,' and the present experiments fully confirm his result. Ammonium 

 chloride may be added in considerable quantity along with the sulphate, 

 or it may be employed in place of it ; the resulting deposits and the 

 numerical results obtained are in all cases excellent. There is a point to 



' Zeits. Electrochem., 1 894, p. 194. 



