ON ELECTROLYTIC METHODS OF QUANTITATIVE ANALYSIS, 253 
The normal decomposition can be represented by the equation :— 
fo Na 
2 SbCS Na = 8d,4+3Na,S48s. 
S Na Cathode Anode 
The separation of sulphur at the cathode must be due to a secondary 
decomposition, which is prevented provided there is a certain excess of 
the sulphide present. It appears immaterial whether this excess is 
increased or not, for in Nos. 9, 10, and 11 three times as much sulphide 
was added as in Nos. 12, 15, and 14 for the same quantities of antimony. 
From this the method is reliable, provided 30 c.c. of sodium sulphide of 
sp. gr. 118 are added for every 0-2 grme. of antimony, and up to 50 c.c. 
can be used with safety. Classen and others recommend this proportion ; 
the above experiments point out the necessity for it. 
The current density of 0°15 to 0:20 ampere per 100 sq. cm. should not 
be exceeded, otherwise the metal does not adhere so well to the electrode. 
The completion of the deposition is best tested by withdrawing a little of 
the solution from the dish with a capillary tube, and testing it with acid 
for the presence of antimony sulphide. 
The addition of caustic soda to the sodium sulphide has no disadvan- 
tageous effect on the method as described. Under similar conditions to 
the above, in which 30 c.c. of sulphide solution and 2 grme. of sodium 
hydrate were added, 0:1514 grme. antimony were found for 0:1515 taken. 
Caustic soda is added in the separation of antimony and tin electrolyti- 
cally, hence it was desirable to ascertain its influence, if any. 
The solutions of the sulpho-salt were quite free from polysulphides, but 
should these be present they must be oxidised with hydrogen peroxide. 
Series IT. 
Deposition of Antimony from a WARM Solution of the Sulpho. sult. 
The time required for the deposition of antimony is considerably 
shortened by conducting the electrolysis in the warm solution. The 
antimony solution is treated with sodium sulphide as described, and 
electrolysed with acurrent of 1 ampere ; 0:2 grme. of metal can be readily 
deposited in 24 hours. Under the right conditions the deposit is bright 
and metallic in appearance. The following table records the results 
obtained :— 
- _ | Sodium | 
Experi- | Antimony | Antimony | suiphide. C.D.49)  |E.M.¥.| Tempera- | Time: | 
ment takea: fond: Solution Amperes Volts ture hours | 
Grme. Grine, | added 
1 02020 | 02090 | 30c.c. 0-98 61 | 50°-60° | 23 
2 02020 | 02028 | 50c.e. 104 6:5 | 50°-60° | 24 
3 0 1010 071009 | 50ce. 1:00 G7 0°65" |) Be 
4 0:0505 0:0502 | 50 c.c. 0-94 6-7 | 50°65° | 22 
5 0-0202 00213 | 50ce. 0:97 6-4 | 50°65° | 2k 
6 0-0101 00093 | 50 c.c. 1-01 64 | 50°65° | 25 
7 02020 | 02000 | 50c.. 1:03 61 | so°-90° | 25 | 
The deposits in Nos. 1 and 7 were dull and dark coloured ; this is to be 
traced to an insufficiency of sodium sulphide in No. 1, and too high a tem- 
perature in No.7. With 50 c.c. of sodium sulphide solution the method 
