302 REPORT — 1898. 



siphon arrangement for decanting and washing without interruption of 

 the current. After thorough rinsing with distilled water, and draining, 

 the deposits were next treated with a few cubic centimetres of absolute 

 alcohol, and finally dried in the steam oven. In each case the outside of 

 the basin was carefully wiped clean and rubbed with chamois leather. 

 Previous to beginning a determination the clean basins were not ignited, 

 but treated in the same way as when they contained deposits, in order that 

 the two weighings might be made under as nearly as possible similar con- 

 ditions. It was found that basins, cleaned by hydrochloric acid and ti-eated 

 as above, fluctuated in weight both upwards and downwards on successive 

 occasions. This at first seemed to indicate considerable liability to error, 

 and yet very concordant results were obtained. The discrepancies would 

 seem to be due to the difficulty of removing the last traces of a deposit by 

 means of hydrochloric acid. It almost appears as if slight alloying took 

 place, for the surface of the platinum becomes marked up to the level at 

 which the liquid has stood during several experiments. From time to 

 time the basins were cleaned as thoroughly as possible by means of nitric 

 acid, ignition, treatment with concentrated hydrochloric acid, &c. 



The substances to be added to the solution must of course be free from 

 any metal which can be deposited electro! ytically. Those employed were 

 tested by means of ammonium sulphide and also by performing a blank 

 experiment. Both the ammonium sulphate and the ammonia were em- 

 ployed in the form of ' 20 per cent.' solutions, i.e. 100 c.c. contained 20 grme. 

 of substance. The required quantities were measured out approximately 

 in graduated tubes or pipettes, and the total volume made up to 130 c.c, 

 or whatever volume was desired, by adding the necessary quantity of dis- 

 tilled water. 



Determination of Nickel. 



The determination of nickel by the ammonium sulphate and ammo- 

 nia method presents no great difficulty, and exceedingly good results are 

 easily obtainable in ordinary circumstances. The first experiments were 

 carried out in order to determine the general conditions under which the 

 best results are obtained. From these the following were adopted as 

 standard conditions for quantities of nickel ranging from O'l to 0*5 grme. 

 or more, the volume of solution in that case being always about 130 to 

 135 c.c. :— 



Substances added to Solution : 5 grme. of ammonium sulphate (25 c.c. 

 of stock solution), and 5 grme. of ammonia (25 c.c. of stock solution). 



Current : 0"5-0'8 ampere per 100 sq. cm. of cathode ; potential differ- 

 ence of electrodes 3-3-5 volts. 



Temperature: Ordinary temperature of laboratory (15°-30°C. In 

 warm weather the temperature rises to the latter amount by the heating 

 effect of the current). 



Ti7ne : 3^-4 hours. 



Under these conditions the metal is completely separated as a fii-mly 

 adherent, well-coloured, and reguline deposit, entirely soluble in dilute 

 hydrochloric acid. In appearance it differs but slightly from the interior 

 surface of the basin. It undergoes no apparent change when left for 

 several days exposed to air, and the weight also remains constant. In 

 successive or simultaneous experiments results are frequently obtained 

 differing by less than would correspond to 0-0001 grme. in the weight of 

 the deposit. 



