88a Dr. watson’s Experiments and 
A little tin added to a mixture of lead and bifmuth, or to 
a mixture of lilver and lead, immediately takes away 
from the refpeifive mixtures the faculty of forming; 
coloured pellicles. 
This quality of tin has hitherto, as far as I know, been 
unobferved; but every new fact, relative to the actions 
of bodies one upon another, ought to be recorded. The 
change produced in lead by the admixture of a fmall 
portion of tin is much felt by the plumbers, as it makes 
the metal fo hard and harfh, that it is not without diffi- 
culty they can call it into ffieet lead. If their old lead 
does not work fo willingly, nor exhibit colours fo readily, 
as new lead, they may refer the difference to the fmall 
quantity of tin contained in the folder, from which old 
lead can feldom be thoroughly freed^ 
With refpedt to the order in which the colours fucceed 
one another upon the furface of melted lead, it feems to 
be the following one; yellow, purple, blue, yellow, pur- 
ple, green, pink, green, pink, green. Upon exhibiting 
the bright furface of melted lead to the air, I have often 
obferved thefe ten changes to follow one another in a 
more or lefs rapid fucceffion, according to the degree of 
heat prevailing in the lead. If the heat is but fmall, the 
fucceffion flops before it has gone through all the 
changes ; but with the greatefl heat I did not obferve any 
further 
