A solution of this substance in distilled vinegar affords permanent crystals, which are improperly called _distilled verdigris_, and are made into a green paint. Verdigris is principally consumed by dyers in combination with logwood, for striking a black colour. It is a virulent poison. Oxide of copper is employed for giving a beautiful green colour to porcelain. It also imparts the same colour to glass, and hence is frequently employed for the formation of artificial emeralds. _Alloys of Copper._ Of all metals that are known, copper is the most susceptible of alloy. The most frequent and useful of these alloys are made with copper and zinc, in different proportions. _Brass_ is an alloy composed of three parts of copper, and about a fourth part of zinc (241). It is a beautiful, useful, and well─known yellow metal. Not being so apt to tarnish and rust as copper, and being, in other respects, better adapted for the purpose than that metal, it is much used for clock─work, and for mathematical and astronomical instruments. It is more ductile than either copper or iron, and hence is peculiarly fitted to be made into wire, for the strings of musical instruments, and other purposes. Sieves are woven with brass wire, after the manner of cambric weaving, and of such extreme fineness that similar ones could not possibly be made with copper wire. Brass wire, flatted and gilded, is sometimes made into lace. The finest brass is manufactured at Geneva. It unites great beauty of colour to a high degree of ductility; and is used chiefly for escapement wheels, and other nicer parts of watch─making. For work in which there is no friction it is necessary to cover brass with a kind of varnish or _laquer_, to improve its colour, and prevent it from being tarnished by exposure to the atmosphere. _Prince’s Metal_, or _Pinchbeck_, is an alloy containing three parts of zinc (241), and four of copper. This metal has nearly the same colour as gold, and was formerly much in use for the manufacture of ornamental articles of different kinds. _Dutch Gold_ is formed by the cementation of copper─plates with calamine (241), hammered out into leaves. This article is chiefly manufactured in Holland and Germany, and has about five times the thickness of gold leaf. _Bronze_, and _the metal of which cannons are made_, consist of from six to twelve parts of tin (238) combined with 100 parts of copper. This alloy is brittle, heavier than copper, and of a yellow colour. Before the method of working iron was brought to perfection, it was used by the ancients for the manufacture of sharp─pointed instruments; and it is supposed to have been the _æs_ or brass of the Romans. _Bell Metal_, or the metal of which bells are formed, is usually composed of three parts of copper and one of tin. Its colour is greyish white; and it is very hard, sonorous, and elastic.