414 PRINCIPLES OP CHEMISTRY 



large quantity is used in the galvanoplastic process, tvhich consists in 

 the deposition of copper from a solution of cupric sulphate by tho 

 action of a galvanic current, when the metallic copper is deposited 

 on the negative pole and takes the shape of the latter. The d- 

 ficription of the processes of galvanoplastic art introduced by Jacobi 

 in St. Petersburg forms a part "of applied physics, and will not be 

 touched on here, and we will only mention that, although first intro- 

 duced for small articles, it is now used for such articles as type moulds 

 (cliches], for maps, prints, &c., and also for large statues, and for the 

 deposition of iron, zinc, nickel, gold, silver, tfec. on other metals and 

 materials. The beginning of the application of the galvanic current to 

 the practical extraction of metals from solutions has also been estab- 

 lished, especially since the dynamo- electric machines of Gramme, 

 Siemens, and others have rendered it possible to cheaply convert the 

 mechanical motion of the steam engine into an electric current. It is 

 to be expected that the application of the electric current, which has 

 long since given such important results in chemistry, will, in the near 

 future, play an important part in technical processes, the example being 

 fihown by electric lighting. 



The alloys of copper with certain metals, and especially with zinc 

 *nd tin, are easily formed by directly melting the metals together. 

 They are easily cast into moulds, forged, and worked like copper, 

 whilst they are much more durable in the air, and are therefore fre- 

 quently used in the arts. Even the ancients used exclusively alloys 

 of copper, and not pure copper, but its alloys with tin or different 

 kinds of bronze (Chapter XVIII., Note 35). The alloys of copper with 

 zinc are called brass or ' yellow metal.' Brass contains about 32 p.c. of 

 zinc ; generally, however, it does not contain more than 65 p.c. of 

 copper. The remainder is composed of lead and tin, which usually 

 occur, although in small quantities, in brass. Yellow metal contains 

 about 40 p.c. of zinc. 12 The addition of zinc to copper changes the 



12 Among tha alloys of copper resembling brass, delta metal, invented by A. Dick 

 (London) is largely used (since 1883). It contains 65 p.c. Cu, and 41 p.c. Zn, the 

 Remaining 4 p.c. being composed of iron (as much as 3J p.c., which is first alloyed with 

 .zinc), or of cobalt, and manganese, afcd certain other metals. The sp. gr. of delta metal 

 is &'4. It melts at 950, and then becomes so fluid that it fills up all the cavities in a 

 'mould and forms excellent castings. It has a tensile strength of 70 kilos per sq. mm. 

 (gun metal about 20, phosphor bronze about 80). It is very soft, especially when heated 

 to 600, but after forging and rolling it becomes very liard ; it is more difficultly acted 

 Upon by air and water than other kinds of brass, and preserves its golden yellow colour 

 for any length of time, especially if well polished. 'It is used for making bearing's, screw 

 propellers, valves, and many other articles. In general the alloys of Cu and Zn con- 

 taining about | p.c. by weight of copper were for a long time almost exclusively made io 

 Sweden and England (Bristol, Birmingham). These alloys for the most part are cheaper, 

 Larder, and more fusible than copper alone, and form good castings. The alloys con- 



