2538 REPORT—1896. 
dish, and the results are altogether more reliable. A current of 0:3 
ampere is best, and 18-19 hours must be allowed for the complete deposi- 
tion even of such small quantities as taken in Nos, 10, 11, 12, for the last 
traces are only very slowly separated from solution. If a stronger current 
(1:0 ampere) be employed the deposit does not adhere properly. The only 
way to tell whether the deposition is complete is to expose a fresh portion 
of the surface of the cathode to the solution, by diluting the contents of 
the dish, and to observe whether any more metal is separated after con- 
tinuing the passage of the current for one hour ; none of the ordinary 
tests for tin are sufficiently delicate to indicate the completion of the 
electrolysis. A comparison of Nos. 13, 14, 15, in which the amount of 
acetic acid added was varied, show that from 15-25 c.c. of a 50 per cent. 
solution of acetic acid is mostfavourable. The larger quantity was found 
the more reliable. 
This method may be regarded as giving accurate results under the 
conditions mentioned ; but it is extremely important to keep the current 
steady, and not to exceed 0°3 to 0-4 ampere per 100 sq. cm. of cathode 
surface, otherwise it is impossible to be certain of a firm deposit. 
Series LY. 
Ammonium Ovalate Solution in Presence of Oxalie Acid and 
Hydroxylamine Sulphate. 
Engel (/oc. cit.) has recently shown that the electrolytic determination 
of tin is accurately effected in a neutral solution, either by the addition of 
hydroxylamine sulphate alone, or of the sulphate or hydrochloride in addi- 
tion to ammonium acetate and tartaric acid. The presence of such a 
reducing agent as hydroxylamine prevents the separation of stannic acid 
during the electrolysis. Such an action is just what is required to render 
the deposition of tin from ammonium oxalate solution reliable, and the 
following experiments show that it acts favourably in the desired direction. 
a oo: | 
d= st Oxdio toes 
| z nes xa es 
, Tin Tin AES ace a0 , ae 
Experi- toler . | found: | 825 mem piece lene ag0 pte ae 
ment | (Grime. Ginie BS eet cadeds ne Ampere olts hours 
] < ~ 
zs rt c.c. a | 
“ es 
— eee — ~ 2 — 1 SSS ee aa — = 
1 06986 | 0.0980 so “| 40 0-4 0:26 2:8 185 
2 0:0986 | 0-0981 80 40 O-4 0:26 2°8 195 
3 0:0986 | 00986 | 8a 40 O-4 0:27 3:0 195 
4 00493 | 0:0497 | 80 40 0-4 0:26 31 19 
5 01972 | 0:1946 | 80 40 0-4 0:27 3-0 19 
ii | if 
The previously mentioned solutions of ammonium oxalate (40 grme. 
per litre) and of oxalic acid (80 grme. per litre) were used in these experi- 
ments, and the tin solution was prepared as described. The solution of 
stannous chloride was neutralised before the addition of the reagents. A 
small current was purposely employed in order to secure a firm deposit ; 
the deposit obtained was quite satisfactory in all cases. The deposition 
is incomplete in No. 5, showing that an increase of current or continuation 
of the electrolysis was required. In each experiment the solution had 
become alkaline, however, and this fact is undoubtedly the cause of the 
slow rate of deposition. The results are interesting, inasmuch as they 
show the possibility of keeping the tin in solution during the electrolysis, 
