1831 .] On the supposed Adulteration of Banca Tin . 
333 
them unfit for the purposes to which tin is applied in commerce and the arts, and 
thus depreciate the value of the Banca Tin in the markets of China or of Europe. 
Knowing that the subject was of considerable importance to the mercantile 
world, I did not confine myself to such a rough mode of testing as is usual with 
the assayers of this metal in Cornwall, who pronounce at once upon its quality 
from its colour, weight, and malleability ; but went through a chemical analysis 
of each specimen, wherein it was nearly impossible to be deceived as to the presence 
of any other metal in any influential proportion. 
The following table presents the results ; the second column shews the specific 
gravities of the several samples taken after they had been melted, cleaned, and 
laminated, and also the appearance of the edge of the strap, though it is difficult to 
say whether the slight roughnesses or cracks were owing to inferior malleability . 
1 should rather sav that all of the samples were perfectly soft and equally ductile. 
Slight variations in the specific gravity from 7. 30 @ 7. 35 may perhaps be unavoid- 
ably due to different degrees of condensation of the same quality of tin under the 
hammer or the roller. But as the admixture of even five per cent, of lead brings 
the specific gravity up to 7.4, and every addition becomes more and more percepti- 
ble in the increase of weight, this mode of testing the metal would of itself 
probably answer every purpose of commerce; while the operation, from its sim- 
plicity, is within the reach of those unacquainted with chemical processes. 1 he 
readiest manner of ascertaining the specific gravity, and satisfying purch.iseis as to 
the absence of lead, is to have a large sized bullet mould with a small oiifice, from 
which a clean bullet can be cut off when cast in it. The buyer or seller may then 
melt a standard muster of pure tin, and cast it in the mould fust, to serve as a 
comparison for the rest : if the tin of commerce give a bullet of the same weig it, 
it may be esteemed pure, (provided always that it is perfectly malleable ,) it it is 
heavier, it may be suspected to be adulterated with lead, and the proportion may 
he readily calculated from the table of specific gravities here subjoined : 
Specific gravity of alloys of Tin and Lead. 
Pure Tin. Pure Lead. Specific gravity at 80°. Diff. 
100 mixed with 
95 ditto 
90 ditto 
85 ditto 
”5 ditto 
*>6.6 ditto 
50 ditto 
0 ditto 
0 by experiment, 
5 ditto, 
10 ditto, 
15 ditto, 
7.30 
7.39 
7.48 
7.62 
7.94 
8.16 
8.82 
11.40 
.09 
.09 
.14 
.32 
25 (by Bishop Watson), 
33.3 ditto, 
50 ditto, 
" 100 ^r n 
If may be assumed, that each addition of one per cent, of lead, up to .> per 
the latter, increases the specific gravity of tin 0.02, or ^th part. 
, T ° the bullet-trial should also added a trial of the homogeneousness of tne 
1 ^ = °ts : this is simply ascertained by striking them with a mallet . if . 8 
c earl y, they may be judged to be solid and good ; but if they emit a u un 
*° Und » there is room for suspicion of fraudulent admixture witlun, an 
^ u 'd be either cut in half, or remelted for the satisfaction of the pu t j n 
Resides lead, there is no metal that it can be worth while to a u e ’ 
Unlesa it be zinc (spelter), and the presence of the latter would be as er . 
W of its impairing considerably the “^^^^nerfectly good in a 
merf 1 1 t0 the P resent sam P les > 1 should P ron ° unce f 25 C en t . on their 
mitile sense ; and by no means liable to the deduction - pn taffe of lead in 
u Ue > stated to have been exacted in the China market : each per cc e 
