256 REPORT—1896. 
this, were it not that the deposit then obtained is always more or less 
powdery in form, and does not adhere sufficiently well to the dish to admit 
of being washed without loss. The method can be made to yield fair 
results if the solution be kept jus? acid throughout the electrolysis by the 
‘addition of oxalic or acetic acid from time to time, as required (Series IT.) ; 
but such a procedure requires constant attention, thus withdrawing at 
once one of the most marked advantages of electrolytic analysis. 
The tin solution used in the following experiments was prepared by dis- 
solving pure tin in pure hydrochloric acid, the acid solution being neutra- 
lised with ammonium hydrate before use and diluted to 175 ¢.c. The 
other solutions employed were : — 
Ammonium oxalate . : . 40 grme. per 1000 c.c. 
Oxalic acid . : ‘ ‘ . 80 BX - 
Aceticacid . : i ‘: . 50 per cent. solution. 
PRELIMINARY EXPERIMENTS, in which 120 c.c. of the ammonium oxalate 
solution were added for 0:1 grme. of tin, showed that the solution be- 
comes alkaline and separates stannic acid after 6 hours, during which 
time only 60-70 per cent. of the metal is precipitated. The decomposition 
may be represented by the equation :— 
.. CO.ONH, , CO.0\ g 
CY GG.ONE,  CO.07 2 tem Nas 200 
Cathode Anode 
(ii.) 2NH, +2CO, + 20,0 =2NH,. HCO,. 
Hence the alkalinity of the solution, which must be overcome to pre- 
vent the precipitation of stannic acid. 
EXPERIMENTAL Data. 
Series I. 
Ammonium Oxalate Solution Acidified with Ovalic Acid. 
{ ‘ Tin Ammonium Oxali id 
Experi- | Tin taken: bond’ oxalate xalic aci Fak pe EMF. | Time: 
ment Grme. ae ‘| solution | Selotion | Ampere | Volts | hours 
| rme. | added, c.c. added, c.c. 
1 | 0:1050 0:0670 | 100 50 0-4 3-4 5 
2 00525 | 0:0247 | 100 50 O-4 30 5L 
3. | 0:1050 | 0-0669 100 50 0:3 3-2 gi 
4 , 00201 | 00158 ; 100 50 0:3 32 gi 
5 | 01026 | 01015 80 40 02-0 | 28-37] 8 
6 01026 | 01009 80 40 0:25-0°5 | 26-32 | 84 
7 | 01026 | 0:0939 80 40 0°24-0°52 | 28-35] 9 
8 01026 | 0:0849 | 80 40 0:23-0°5 | 33-35] 9 
9 01050 | 0:1030 100 50 0°9-1-2 35 6 
10 0-1¢50 | 01042 | 100 50 0-5-1-0 35 7 
11 0:1050 | 0-:0740 100 50 0-8-1 0 35 6 hot | 
12 01575 | 01526 | 100 50 0-5 2-8 9 hot | 
13. | 01050 | 0:1055 100 75 0-5 27 5} 
14 01575 | 01250 100 15 05 2:6 5L 
15 02100 | 02061 100 5) 0:5-1:0 | 31-38 | 6% | 
The above results are taken from forty-five experiments carried out. 
In each case the electrolysis was continued until after the solution became 
alkaline ; after the solution has turned alkaline, the further deposition of tin 
is extremely slow, only 2-3 m. grmes. being deposited by a current of 0-5 
ampere in twelve hours. Although a few fair results are recorded above 
