37
the zinc forms a considerable proportion. The solder oflead and tinplate is an a'iioy oflead and tin, and that of tin is the same alloy with a little bismuth. Tinning, gilding,and silvering may also be reckoned a species of alloys, since the tin, gold, and silver aresuperficially united in these cases to other metals.
Metallic alloys possess usually more tenacity than could be inferred from their con-stituents ; thus, an alloy of twelve parts of lead with one of zinc has a tenacity doublethat of zinc. Metallic alloys are much more easily oxydized than the separate metals, aphenomenon which may be ascribed to the increase of affinity for oxygen which resultsfrom the'tendency of the one of the oxydes to combine with the other. An alloy of tinand lead heated to redness takes fire, and continues to burn for some time like a pieceof bad turf.
Every alloy is,* in reference to the arts and manufactures, a new metal, on account ofits chemical and physical properties. A vast field here remains to be explored. Not abovesixty alloys have been studied by the chemists out of many hundred which maybe made;and of these very few have yet been practically employed. Very slight modificationsoften constitute very valuable improvements upon metallic bodies. Thus, the brass mostesteemed by turners at the lathe contains from two to three per cent, of lead; but suchbrass does not work well under tile hammer; and, reciprocally, the brass which is bestunder the hammer is too tough for turning.
That metallic alloys tend to be formed in definite proportions of their constituents isclear from the circumstance that the native gold of the auriferous sands is an alloy withsilver, in the ratios of 1 atom of silver united to 4, 5,6,12 atoms of gold, but never witha fractional part of an atom. Also, in making an amalgam of 1 part of silver with 12or 15 of mercury, and afterwards squeezing the mixture through chamois leather, theamalgam separates into 2 parts : one, containing a small proportion of silver and muchmercury, passes through the skin; and the other, formed of 1 of silver and 8 of mercury,is a compound in definite proportions, which crystallizes readily, and remains in the knotof the bag. An analogous separation takes place in the tinning of mirrors ; for on load-ing them with the weights, a liquid amalgam of tin is squeezed out, while another amal-gam remains in a solid form composed of tin and mercury in uniform atomic proportions.But, as alloys are generally soluble, so to speak, in each other, this definiteness of com-bination is masked and disappears in most cases.
M. Chaudet has made some experiments on the means of detecting-the metals ofalloys by the cupelling furnace, and.they promise useful applications. The testingdepends upon Ihe appearances exhibited by the metals and their alloys when heated on a^Pel. Pure tin, when heated this way, fuses, becomes of a grayish black color, fumesa little, exhibits incandescent points on its surface, and leaves an oxyde, which, when■Withdrawn from the fire, is at first lemon-yellow, but when cold, white. Antimonyjnelts, preserves its brilliancy, fumes, and leaves the vessel colored lemon-yellow when*°t, but colorless when cold, except a few spots of a rose tint. Zinc burns brilliantly,® Cone of oxyde; and the oxyde, much increased in volume, is, when hot, green-8 j “it when cold, perfectly white. Bismuth fumes, becomes covered with a coat ofebed oxyde, part of which sublimes, and the rest enters the pores of the cupel; when? u, the cupel is of a fine yellow color, with spots of a greenish hue. Lead resemblesismuth very much; the cold cupel is of a lemon-yellow color. Copper melts, and be-mes covered with a coat of black oxyde; sometimes spots of a rose tint remain on the
hav e “T~J in 75 > antimony 25, melt, become covered with a«coat of black oxyde,very few incandescent points; when cold, the oxyde is nearly black, in con-
this w' e -°^ *Be nctinn of the antimony : a part of antimony may be ascertained incu Pel "V** e aiI °y- An uHoy of antimony, containing tin, leaves oxyde of tin in theoxyil e "Too P art °ftin may be detected in this way. An alloy of tin and zinc gives anAn ai] ov 1Ca ’ while hot, is of a green tint, and resembles philosophic wool in appearance,and g a ^ conta ining 99 tin, 1 zinc, did not present the incandescent points of pure tin,of a gr a y aa °xyde of greenish tint when cold. Tin 95 , bismuth 5 parts, gave an oxydeand ti nj (.q 0 .• Tin and lead give an oxyde of a rusty brown color. An alloy of leadclean si rf " tai !'.‘ns? only 1 per cent, of the latter metal, when heated, does not expose a25, did not m i e * e ad, but is covered at times with oxyde of tin. Tin 75, and copperthe oxyde j s .Save a black oxyde : if the heat be much elevated, the under part ofThe cupel becom^ and is oxyde of tin ; the upper is black, and comes from the copper.By it is marked me - S a rose color. If the tin be impure from iron, the oxyde producedThe degree of^m 81 ? 018 a rust color.
greater or less f ac -?. 1% Between metals may be in some measure estimated by thethey unite, or \vith it5 v' vitl1 w Bich, when of different degrees of fusibility or volatility,less tendency to sen'™' 011 - tlley can ’ a *" ter un i° n > Be separated by heat. The greater ormay also give some rat J: * nt0 differently proportioned alloys, by long 5 continued fusion,information upon the subject. Mr. Hatchett remarked, in his