Page:The American Cyclopædia (1879) Volume I.djvu/360

 336 ALLOY ing temperature of one of them. An alloy of tin and copper may be thus treated, the tin melting at 442, and the copper at 1,996. This "sweating process," called liquation, is used to separate silver from copper. Lead is first melted in with the other metals, and when sweated out it takes the silver along with it. This alloy is then separated by another process, depending on the easy oxidation of the lead. An interesting property of the metals, which may seem somewhat opposed to the one just de- scribed, is the tendency of one, when melting, however fusible it may be, to cause any other in contact with it, however infusible, to dis- solve in the melted metal ; its surfaces are washed away, till nothing solid is left. Pla- tinum, which is among the most difficult met- als to melt, is very susceptible of injury from this cause. The costly crucible and other vessels of the chemist may be ruined in an unguarded moment by contact with other metals highly heated. On this property is based the principle of soldering two pieces of metal by means of a third. Their surfaces are fixed together by interposing an alloy which is more fusible than either of the metals to be joined ; and this must also consist of metals which are disposed to unite and form a new alloy with them. Pieces of gold are soldered together with an alloy of gold with silver or with copper; articles of silver with an alloy of sil ver and copper ; of copper, with an alloy called hard solder, which is brass containing a large proportion of zinc. Another interesting prop- erty of alloys is the different effects produced by the order in which their component parts have been mixed, the proportions continuing the same. Ten parts of antimony added to 90 of tin and 10 of copper, make a compound of very different physical properties from that produced by adding 90 parts of tin to 10 of copper and 10 of antimony. This appears to be analogous to what we witness in vegetable chemistry, as in the identity of composition in starch and sugar. The alloys already in use are very numerous, and new valuable combina- tions are continually discovered. Those alone of copper with zinc form a long list, in which we find the names of many very useful com- pounds, some of them known from the time of Tubal Cain. Pewter has long been a useful, though a very homely alloy. It is made of dif- ferent combinations of lead and tin, sometimes with additions of antimony, bismuth, and cop- per, and in this case is known in trade under different fanciful names, as britannia, &c. Ger- man silver, composed of copper, nickel, and usually zinc, has in part displaced it, and is likely to be itself displaced by some improved combinations. Muntz's yellow metal is an alloy of 60 parts of copper to 40 of zinc. These pro- portions may be slightly varied, but they are the ones specially recommended in the patent, as producing a composition more easily rolled into sheets while hot. It is used for sheathing the bottoms of ships. In importance, no alloys can rank higher than those of which printers' types are made, and no known metal possesses the properties essential to them. ' They consist of lead and antimony, in proportions varying with the kind of types. For very fine types tin is added, to increase the fusibility and consequently to make the metal flow better, so as to fill the finest details of the mould. Many type founders introduce also some copper, by first alloying it with the antimony; this in- creases the durability of the type considerably. The noble metals, gold and silver, are too soft to be used in a pure state. They are alloyed with copper to give them hardness, and gold also with silver. The standard silver of Great Brit- ain consists of silver 11 -10, and copper 0'90. The French silver plate contains 9 '5 parts of silver and 0'5 copper; trinkets, 8 parts of sil- ver to 2 of copper. In the United States these alloys are made as rich or as poor as the indi- vidual manufacturer judges best for his inter- est. His reputation is the only guarantee that his work is what it is sold for. There is no test but actual analysis, and this is not appli- cable to the articles without destroying part of them. Specific gravity may be employed to some extent, but as the alloy often has a some- what different density from that of the mean of its metals, the calculation gives an approxi- mation more or less correct according to cir- cumstances. The following rule given by Dr. Van der Weyde may be used to find the spe- cific gravity of an alloy made of any number of metals, mixed in whatever proportion : " Find the relative volume of each metal by dividing its weight by its specific gravity ; the sum of all the weights divided by the sum of the volumes gives the specific gravity of the alloy." An alloy which closely resembles gold in color, specific gravity, and ductility, is made of 16 parts of platinum, 7 parts of copper, and 1 of zinc. These are put into a crucible, cov- ered with charcoal powder, and melted. Its cost is scarcely one fourth of that of gold. The so-called oroide gold is a very base alloy, only resembling gold in color if kept clean, and is easily distinguished from it by having scarce- ly half its specific gravity. It is said to be made by melting copper 100 parts, tin 17, magnesia 6, carbonate of potash 9 or salt of antimony 8'6, and quicklime 1 '6. The latest im- provement is the so-called sterrometal, invented by Rosthorn in Vienna ; it is made by melting 600 Ibs. copper with 2 Ibs. cast iron; when fluid there is added 36 Ibs. zinc and 4 oz. borax. It is asserted that it is,8,000 Ibs. stronger per square inch than the best wrought iron. Al- exander Birchholz of Hartford, Conn., has pat- ented the same alloy, and erected a factory in Providence, R. I. Among interesting ap- plications of alloys we must mention the plates of easily fusible metals with which steam boilers are sometimes provided, offering an additional safety besides the safety valve, as they will melt at a temperature corresponding with too high a pressure. Another application