ALLOYS OF COPPER. 585 



in fine blue crystals, containing 8HO. Verdigris is a subacetate 

 of copper, formed by placing plates of the metal in contact 

 with the fermenting marc of the grape, or with cloth dipt in 

 vinegar. The bluer species, which consists of minute crystal- 

 line plates, is a definite compound of 1 eq. acetic acid, 2 eq. 

 oxide of copper, and 6 eq. of water, CuO, (C 4 H 3 O 3 ), CuO + 

 6 HO. The ordinary green species is a mixture of sesqui and 

 tribasic acetates of copper, with the preceding bibasic acetate. 

 Water dissolves out from verdigris the sesquiacetate, which pre- 

 sents itself on evaporating the solution, sometimes as an amor- 

 phous mass, and sometimes in crystalline grains of a pale blue 

 colour. It consists of 2 eq. of acetic acid, 3 eq. of oxide of 

 copper and 6 eq. of water; it loses 3 eq. of water at 212. The 

 tribasic acetate is the insoluble residue which remains, after 

 the lixiviation of verdigris. It is a clear green powder, which 

 loses nothing at 212. It contains 2 eq. of acetic acid, G eq. 

 oxide of copper, and 3 eq. of water. (Berzelius). 



Acetate of copper also combines with acetate of lime, and 

 with several other salts. The double acetate and arsenite of 

 copper, is a crystalline powder of a brilliant sea-green colour, 

 which is used as a pigment, under the name of the green of 

 Schweinfurth. It is obtained by mixing boiling solutions of 

 equal parts of arsenious acid, and the neutral acetate of copper, 

 adding to the mixture its own volume of cold water, and leaving 

 the whole at rest for several days. It is a highly poisonous 

 substance. From the analysis of Ehrmann its formula is Cu O, 

 (C 4 H 3 3 )+3(CuO,As0 3 ). 



The most important alloys of copper are those with tin and zinc: 

 100 parts copper with 10 tin, form bronze and gun metal. 

 100 parts copper with 20 to 25 tin, form bell metal. 

 100 parts copper with 30 to 35 tin, form speculum metal. 

 A little arsenic is generally added to the last alloy, to increase 

 its whiteness. 



The different varieties of brass are prepared, either by fusing 

 together the two metals, copper and zinc, or by heating copper 

 under a mixture of charcoal and calamine, an operation in which 

 zinc is reduced and its vapour absorbed by the copper. Two or 

 three parts of copper to one of zinc form common brass ; equal 

 parts of copper and zinc, or four of the former and one of the 

 latter, give an alloy of a higher colour resembling gold, and on 

 that account called similor. 



