It will be noticed that when cavities are lined with tin foil, it only constitutes a small part of the filling, and that it has not been melted with the other metals in the alloy before being amalgamated. A thick mat of tin has been recommended as a partial non-conductor under amalgam fillings. Plastic tin can be made by pouring mercury into melted tin, or by mixing the fillings with mercury at ordinary temperatures; it has a whitish color, and if there is not too much mercury it occurs in the form of a brittle granular mass of cubical crystals. Generally amalgams of tin and mercury do not harden sufficiently, but forty-eight parts of mercury and one hundred of tin make a fairly good filling, said to have a therapeutical value; it should not be washed or squeezed before using, and "is not a chemical combination." "Tin unites with mercury in atomic proportions, forming a weak crystalline compound." (Dr. E. C. Kirk.) Mercury and tin readily unite as an amalgam under ordinary circumstances, and form a definite chemical compound having the formula Sn_{2}Hg. (Hodgen.) Another preparation of tin is known as stannous gold; it is manufactured in heavy sheets and used the same as cohesive gold foil, and can be easily manipulated, for it is rather plastic. Crystal tin for taking the place of tin foil: "Take chemically pure hydrochloric acid and dissolve tin foil in it until a saturated solution is obtained; this may be done speedily by heating the acid to a boiling point, or the same thing can be accomplished in a few hours with the acid cold; it is then chlorid of tin. It is then poured into a clean vessel and an equal quantity of distilled water added; then a clean strip of zinc is plunged into the solution, and tin crystals are deposited on the zinc; when there is sufficient thickness on the zinc, remove both, and slip the crystals off from the zinc into pure water, clean the zinc thoroughly, and reinsert for another coating. The character of the crystallization will be modified by the extent of the dilution of the solution in the first place. Wash the tin in pure water until all traces of the acid are removed, or a few drops of ammonia can be added to neutralize the acid. It was suggested that it would be desirable to have some acid remain in the tin for filling teeth in which there is no sensitive dentin. We have put in a few fillings, and it works beautifully, and makes firmer fillings than foil. It must be kept in water (probably alcohol is better). It is pure tin, unites perfectly, and works easier than foil." (Dr. Taft, _Dental Register of the West_, 1859.) For some years it was considered the best practice to enlarge all root-canals and fill them with gold; in many of these cases the crown cavities were filled with tin.