If spirit of salt, or even sea-salt in substance, be added to a solution of Lead in the nitrous acid, a white precipitate immediately falls; which is no other than the Lead united with the marine acid. This precipitate is extremely like the precipitate of Silver made in the same manner, and that being called _Luna cornea_ hath occasioned this to be named _Plumbum corneum_. Like the _luna cornea_ it is very fusible, and being melted hardens like it into a kind of horny substance: it is volatile, and may be reduced by means of inflammable matters combined with alkalis. But it differs from the _luna cornea_ in this chiefly, that it dissolves easily in water; whereas the _luna cornea_, on the contrary, dissolves therein with great difficulty, and in a very small quantity. As this precipitation of Lead from its solution in spirit of nitre is procured by the marine acid, Lead is thereby proved to have a greater affinity with the latter acid than with the former. Yet, if you attempt to dissolve Lead directly by the acid of sea-salt, the solution is not so easily effected as by the spirit of nitre, and it is always imperfect; for it wants one of the conditions essential to every solution in a liquor, namely transparency. If Lead be boiled for a long time in a lixivium of fixed alkali, part of it will be dissolved. Sulphur renders this metal refractory and scarce fusible; and the mass they form when united together is friable. Hence it appears that sulphur acts upon Lead much in the same manner as upon Tin; that is, it renders both these metals less fusible, which are naturally the most fusible of any, while it exceedingly facilitates the fusion of Silver, Copper, and Iron, metals which of themselves flow with the greatest difficulty. CHAP. VIII. _Of_ QUICK-SILVER.