Tin . 
397 
determine the tinning of the copper. The experiment 
however succeeded but imperfectly when tartar was used, 
owing to the languor of its action on iron, and even when 
a few drops of sulphuric acid were added, the tin was 
precipitated solely on die iron, whilst the surface of the 
copper remained unaltered, but with alum it was differ- 
ent. 
11. Some tin -leaf was boiled with a solution of alum 
for half an hour and then withdrawn. Into the solution 
were then introduced a piece of polished copper, and 
some iron filings. The latter were acted on with much 
rapidity, and in a few minutes the copper was covered 
with a pellicle of tin, which in half an hour gave it the 
appearance of fine silver unpolished. 
12. Tin-leaf and a solution of alum were boiled to- 
gether. The tin was then taken out, and into the solu- 
tion both iron and copper were introduced, each polished. 
After a few minutes boiling both these metals were high- 
ly tinned. 
13. Some sulphat of copper was dissolved in water, 
tin-leaf was added, and the mixture was exposed to a 
moderate heat for some days in a well closed phial In 
a few days the colour of the solution entirely disappeared, 
and the copper precipitated to the bottom of the vessel 
The clear supernatant fluid was distributed into three 
phials, into the first of which was put copper and tin ; in- 
to the second, copper and iron ; and into the third, cop- 
per alone. They were well corked, and after digestion 
in moderate heat for some hours the copper in the first 
phial, and the copper and iron in the second were well 
tinned, but the copper in the third remained unaltered. 
From the above experiments we may clearly make out 
that the state of the solution of tin, when it is disposed to 
precipitate in a metallic form on the surface of copper 
