ORF-s OF MOLYBDENUM. 217 



sheets in a vertical position are immersed, first in a vat of grease, and 

 then in B cast iron huh containing about 5 cwt. of melted tin ; they 

 remain in the tin for an hour and a half, and arc then taken out. As 

 there is now two or three times too much tin on the plates, they are 

 made to undergo a process called washing, in a vessel of melted grain 

 tin, by which the excess of tin is removed ; after which they are cleaned 

 and rubbed in bins of dry bran until they receive the characteristic sil- 

 ver polish. 



When tin plate slightly heated is sponged over quickly by an acid, 

 (nitro-muriatic,) the crystalline character of the tin is brought out, and 

 the ware so treated is called ?noirc' metallique. The plate before sub- 

 jecting it to the acid should be well washed with alkali ; and after the 

 action it should be immediately washed in clean water and dried. 



Tin is also used extensively as tinfoil, the sheets of which are about 

 1000th of an inch thick ; also with quicksilver it is used to cover glass 

 in the manufacture of mirrors. It is alloyed with copper in various pro- 

 portions, constituting thus 7 to 10 per cent, of bronze ; 20 per cent, of 

 the ancient bronze for weapons; 20 per cent, of the metal for cymbals 

 and the Chinese gong ; 20 to 30 per cent, of bell metal ; and 30 to 40 

 per cent, of speculum metal. 



The oxyd of tin, as obtained by chemical processes, is employed on 

 account of its hardness for forming a paste for sharpening fine cutting 

 instruments. The chlorid of tin is an important agent in the precipi- 

 tation of many colors as lakes, and in fixing and changing colors in 

 dyeing and calico printing. The bisulphuret of tin has a golden luster, 

 and was termed aurum musivum, or mosaic gold, by the alchemists. 

 It is much used for ornamental painting, for paper hangings and other 

 purposes, under the name of bronze powder. 



Pins are, tinned by boiling them for a few minutes in a solution of 1 

 part of cream tartar, 2 of alum, 2 of common salt, in 10 or 12 of water, 

 to which some tin tilings or finely granulated tin are added. 



Tin medals or castings, are bronzed by being washed over with a 

 solution of 1 part of protosulphate of iron, 1 of sulphate of copper, in 20 

 of water ; this gives a gray tint ; they are then brushed over with a 

 solution of 4 parts of verdigris in 11 of distilled vinegar, and then 

 polished with a soft brush and colcothar. 



6. MOLYBDENUM. 

 Molybdenum occurs in nature as a sulphuret, and sparingly 

 as an oxyd. Also as molybdic acid, in molybdate of lead. 



1. molybdenite. — Sulphuret of Molybdenum. 



In hexagonal crystals, plates, or masses, thin foliated like 

 graphite, and resembling that mineral. Color pure lead- 

 gray ; streak the same, slightly greenish. Thin laminsB 

 very flexible ; not elastic. H=l — 1*5. Gr=4*5 — 4*75. 



In what other way is tin used ? What alloys are made with it 1 

 What are the characters of molybdenite ? 



