296 



REPORT — 1898. 



elusions are contrasted in the sequel. The methods examined were based 

 on the deposition of zinc from a solution containing : — 



i. Sodium pyrophosphate. 



ii. Alkaline oxalate in neutral or alkaline solution. 

 iii. Alkaline oxalate in presence of potassium sulphate. 

 iv. Potassium or ammonium oxalate and free tartaric acid. 

 V. Potassium cyanide. 



vi. Potassium cyanide and sodium phosphate, 

 vii. Ammonium lactate and ammonium sulphate. 



In the following experiments the zinc was always present as sulphate, 

 and the metal was deposited in platinum basins, which were protected 

 from the action of the zinc by a deposit of copper, which extended three 

 or four millimetres beyond the surface of the liquid, during the electrolysis. 

 The basins are coppered by means of a hot solution of copper ammonium 

 oxalate containing free oxalic acid, with a current density of 0'5 to 1 

 ampere ; the operation only requires two or three minutes. Unfortunately, 

 the layer of copper must be renewed for each zinc determination. Experi- 

 ments were made with the object of protecting the platinum with layers 

 of gold or silver, but, on the whole, better results were obtained with th& 

 coppered basins. If the zinc is deposited on the unprotected surface of 

 the platinum a black stain is produced, when the zinc deposit is dissolved 

 in acid. According to Yortmann [Ber. 24, 2753) the black deposit con- 

 sists of finely divided platinum. 



The end of the reaction was generally ascertained by tilting the vessel 

 or increasing the volume of the solution, so that the liquid came in 

 contact with an unaltered layer of copper. In a small number of 

 determinations the end was ascertained by hanging a narrow strip of 

 metallic copper over the side of the basin ; if the colour of the copper 

 remains unchanged, the precipitation of the zinc is complete. As the 

 last traces of zinc are deposited with difficulty the current density is 

 always increased to one ampere at least towards the end of the operation. 

 The deposit was washed with water without interrupting the current. 

 It was finally washed with alcohol and dried at 80°. No signs of oxidation 

 were noticed. 



I. — Deposition of Zinc from Solution of Pyropltospliate. 



Brand's method is simple and accurate. The solution of zinc salt is- 

 mixed with 4 grme. of sodium pyrophosphate and with about 5 c.c. of 

 a saturated solution of ammonium carbonate ; water is added until the 

 liquid measures 120 or 150 c.c, and the mixture is electrolysed. The zinc 

 is obtained as a bright bluish-white deposit, adhering firmly to the basin. 



