xl Historical Sketch of the Physical Sciences, 1818. 
that bismuth may be substituted for lead in the process of puri- 
fying gold and silver by cupellation ; but no accurate experiments 
had been made to determine whether that metal could be 
employed to ascertain exactly the quantity of alloy contained in 
gold and silver. We are indebted to M. Chaudet for solving this 
problem. He has ascertained that the bismuth to be employed 
in such cases must be free from silver; that if it contains 
arsenic, which is commonly the case, a portion of the silver is 
driven off the cupel along with the arsenic and lost: that a 
smaller proportion of bismuth must be employed than is required 
of lead ; and that the cupels employed must be less porous than 
those used when lead is used to separate the alloys from gold or 
silver; because bismuth has the property of inducing so great a 
degree of fluidity into those metals that they are apt to penetrate 
into the pores of an ordinary cupel and to be lost. It follows 
from the experiments of Chaudet, that if these precautions be 
atteaded to, bismuth may be employed as well as lead to deter- 
mine the purity of gold and silver. The following table exhibits 
the quantity of bismuth requisite for purifying one part of silver 
of the degrees of purity marked in the table ; . 
aga Dose of bismuth ‘Ratio between the 
Silver. | Copper. necessary, ‘bismuth and copper. 
1000 Siehvb m 0:0 
950 50 2 40-0 
900 100 3 30:0 
800 200 6 30°0 
BOGEN 300 8 26:6 
600 400 10 25°0 
500 500 i] 22:0 
400 600 12 20:0 
300 700 | 17:0 
200 800 12 15:0 
100 900 12 13°3 
0 1000 8 8-0 
(Ann. de Chim. et Phys. viii. 113.) 
12. Tin.—This metal has so great a tendency to unite with a 
maximum of oxygen that the preparation of its protoxide is 
attended with some difficulty. I have generally succeeded by 
keeping the permuriate of tin in a close vessel in contact with a 
quantity of metallic tin, and then precipitating the protomuriate - 
by ammonia; but this method is not always attended with the 
desired success. M. Cassola has given us a process which he 
assures us never fails. Upon filings of tin, he pours nitric acid 
diluted with ten times its volume of water, and leaves the two 
substances in contact for 48 hours. The tin acquires a brownish- 
