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MIXING PEWTER, TYPE METAL, ETC.
beyond moderation in the heat employed, but the difficulty of making definite and uniform alloys increases when the melting points of the metals, or their qualities or quantities, are widely dissimilar.
In mixing alloys with new metals, it is usual to melt the less fusible first, and subsequently to add the more fusible ; the mixture is then stirred well together, and common opinion seems to be in favour of running the metal into an ingot mould, as the second fusion is considered more thoroughly to incorporate the mixture. Sometimes, with the same view, the alloy is granulated, by pouring it from the crucible into water, either from a considerable height, or over a bundle of birch twigs, which subdivides it into small pieces ; others condemn such practices, and greatly prefer the first fusion, in order to avoid oxidation, and to be nearer to the intended proportions.
But in many, and perhaps in most cases, it is the practice to fill the melting pan, or the crucible, in part with old alloy, consisting of fragments of spoiled or worn-out work ; and to which is added, partly by calculation but principally by trial, a certain quantity of new metals. This is not always done from motives of economy alone, but from the opinion that such mixtures cast and work better than those made entirely of new metals.
When small quantities of a metal of difficult fusion are added to large proportions of others which are much more fusible, the whole quantities are not mixed at once. Thus, in pewter, it would be scarcely possible to throw into the melted tin the half or one per cent. of melted copper with any certainty of the two combining properly, and it is therefore usual to melt the copper in a crucible, and to add to it two or three times its quantity of melted tin: this as it were, dilutes the copper, and makes the alloy known as temper, which may be fused in a ladle, and added in small quantities to the fluid pewter, or to the tin, as the case may be, until on trying a small piece the proportion is considered suitable.
The metal for printer's type is often mixed much in the same manner; the copper is first melted alone in a crucible, the antimony is melted in another crucible, and is poured into the copper, sometimes a little lead is also added. The hard alloy and the tin are then introduced to the mass of type-metal or lead, also in great measure by trial, as old metal mostly enters into the mixture.
MIXING BRITANNIA METAL, BRASS, ETC. In Lardner's Cyclopedia, Manufactures in Metal, Vol. III., p. 103, it states :
“ The composition of Britannia metal is as follows:-3 cwt. of best block tin; 28 lbs. of martial regulus of antimony ; 8 lbs. of copper, and 8 lbs. of brass. The amalgamation of these metals is effected by melting the tin, and raising it just to a red heat in a stout cast-iron pot or trough, and then pouring into it, first the regulus, and afterwards the copper and brass, from the crucibles in which they have been respectively melted, the caster meanwhile stirring the mass about during this operation, in order that the mixture may be complete.”
It would appear, however, much more likely and consistent that a similar mode is adopted in making this alloy, as in pewter and type-metal; namely, that the copper and brass are melted together in one crucible, the antimony then added from another crucible, and perhaps also a little tin; this would dilute the hard metals, and make a fusible compound, to be added to the remainder of the tin when raised a very little beyond its fusing point, so as to maintain fluidity when the whole were mixed and stirred together, previously to being poured into ingots. By this treatment the tin would be much less exposed to waste.
When a very oxidizable or volatile metal, as zinc, is mixed with another metal the fusing point of which is greatly higher, as with copper for making the important alloy brass; whatever weight of each may be put into the crucible, it is scarcely possible to speak with anything like certainty of the proportions of the alloy produced, from the rapid and nearly uncontrollable manner in which the waste occurs.
Various means have been devised at different times for combining these two metals. Thus the author of the article “ Brass," Supplement to Encyclopedia Britannica, says :
“ Although the most direct way of forming the different kinds of brass is by immediately combining the metals together, one of them, which is most properly called brass, was manufactured long before zinc, one of its component parts, was known in its metallic form. The ore of the latter metal was cemented with sheets of copper, charcoal being present. The zinc was formed and united with the copper, without becoming visible in a distinct form. The same method is still practised for making brass.”
VARIOUS MODES OF MAKING BRASS.
Under Emerson's patent the more nearly direct fusion of the two metals was accomplished, as will be seen by the extract*.
The author of the “ Britannica” also states :—“The best way of uniting zinc with copper, in the first instance, will be to introduce the copper in thin slips into the melted zinc, till the alloy requires a tolerable heat to fuse it, and then to unite it with the melted copper."
Some persons thrust the whole of the copper, in thin plates, into the melted zinc, which rapidly dissolves them; and the mass is kept in a pasty condition until within a few minutes of the time of pouring, when they augment the heat to the degree required for the casting process.
But the plan which is the most expeditious, and now most usually adopted, is to thrust the broken lumps of zinc beneath the surface of the melted copper with the tongs, which mode will be more particularly described ; but however conducted, some waste of the zinc will inevitably occur.
It is also certain that each successive fusion wastes, in some degree, the more oxidizable metal, so that the original proportion is more and more departed from, especially with the least excess of heat; and when the metals are not well covered with flux, the loose oxide frequently mixes with the metal. This in brass gives rise to the white-coloured stains, and the little cavities filled with
* “ Patent granted to James Emerson, dated July 13, 1781. “ I take spelter in ingots and melt them down in an iron boiler ; I then run the melted spelter through a ladle with holes in it, fixed over a tub of cold water, by which means the spelter is granulated or sholed, and is then fit for making brass on my plan. I then mix about 54 lbs. of copper shot, about 10 lbs. of calcined calamine ground fine, and about one bushel of ground charcoal together ; I then put into a casting pot a handful of the mixture, and upon it I put about 3 lbs. of the sholed spelter ; I then fill up the pot with the said mixture of copper shot, calcined calamine and ground charcoal. In the same manner I fill eight other pots, so that 54 lbs. of copper shot, 27 lbs. of sholed spelter, about 10 lbs. of calcined calamine, and about i bushel of ground charcoal, make a charge for one furnace, containing 9 pots, for making brass on my plan. My chief reason for using the small quantity of calamine in the process is more for confining the spelter by its weight, than for the sake of any increase arising from it, and I have frequently omitted the calamine in the process.
“ The pots being so filled are respectively put into the furnace, and about 12 hours completes the process, and from this charge I have on the average 82 lbs. of pure fine brass, fit for making ingots or casting plates for making brass battery. wire, or brass latten ; and my brass, made as aforesaid, is of a superior quality to any brass made from copper and calamine."— Repertory of Arts, 1796, vol. 5, p. 24. THE AUTHOR'S EXPERIMENTS ON ALLOYS OF COPPER.
the white oxide of zinc; and in gun-metal the stains and streaks are blacker, and the oxide of tin (or putty powder) being much harder than the former, is sadly destructive to the tools. The vitreous fluxes collect these oxides, and are therefore serviceable; but when in excess, they are liable to run into the mould when the metal is poured. The chemist generally uses covers to the crucibles, to lessen the access of air, and therefore of oxidation; but the founder frequently leaves the brass, &c. entirely uncovered: no considerable waste occurs until the metal is entirely fused, and rather hotter than is required for pouring, which is indicated by the zinc beginning to burn at the surface with a blue flame *.
In collecting the several alloys given at pages 265 to 286, especially those of copper, I found great difficulty in reconciling many of the statements derived from books; and therefore, to place the matter upon a surer basis, and also with some other views, I determined to mix a series of the copper alloys, in quantities of from one to two pounds each, pursuing, as nearly as possible, the common course of foundry-work, to make the results practical and useful.
My first intention was to weigh the metals into the crucible, and to find, by the weight of the product, the amount of loss in each case, as well as the quality of the alloy. Commencing with this view with copper and zinc, the several attempts entirely failed; owing to the extremely volatile nature of the latter metal, especially when exposed to the high temperature of melted copper. The difficulty was greatly increased, owing to the very large extent of surface exposed to the air, compared with that which occurs when greater quantities are dealt with, and the increased rapidity with which the whole was cooled.
The zinc was added to the melted copper in various ways; namely, in solid lumps, in thin sheet hammered into balls, poured in when melted in an iron ladle ; and all these, both whilst the crucible was in the fire and after its removal from the same. The surface of the copper was in some cases covered with glass
... The loss which occurs in melting brass filings is a proof that the granulation of the metals is not always desirable, and unless the brass filings are well drawn, by a group of magnets, to free them from particles of iron and steel, the latter often spoil the castings, as they become so exceedingly hard as to resist the file or turning tool, and can be only removed by the hammer and cold-chisel.
THE AUTHOR'S EXPERIMENTS ON or charcoal, and in others uncovered, but all to no purpose ; as from one eighth to one half the zinc was consumed with most vexatious brilliancy, according to the modes of treatment: and these methods were therefore abandoned as hopeless.
I was the more diverted from the above attempts, by the well known fact that the greatest loss always occurs in the first mixing of the two metals, and which the founder is in general anxious to avoid: thus when a very small quantity of zinc is required, as for so-called copper castings, about 4 oz. of brass are added to every 2 or 3 lbs. of copper. And in ordinary work, a pot of brass weighing 40 lbs., is made up of 10, 20, or 30 lbs. of old brass, and two-thirds of the remainder of copper, these are first melted : a short time before pouring, the one-third of the new metals, or the zinc is plunged in, when the temperature of the mass is such that it just avoids sticking to the iron rod with which it is stirred.
In mixing the copper and zinc for my experiments on brass, an entirely different course was therefore determined upon, namely, to melt the metals on a much larger scale, and in the usual proportion, that is, 24lbs. of copper to 12lbs. of zinc, to learn the first loss of zinc when conducted with ordinary care. Then to remelt a quantity of the alloy over and over again, taking a trial bar each time, in order to ascertain the average loss of zinc in each fusion. From the residue of the original mixture, to make the alloys containing less zinc, by a proportional addition of copper; and those alloys containing more zinc, by a similar addi. tion of zinc. And lastly, to have the whole of the bars assayed, to determine the absolute proportions of copper and zinc contained in each, and from these analyses to select my series of specimens, as nearly in agreement as I could with the proportions in common use. This method answered every expectation*
Twenty-four pounds of copper, namely, clean ship’s bolts, were first meited alone to ascertain the loss sustained by passing through the fire, which was found to be barely 1 oz. on the whole. A similar weight of the same copper was weighed out, and also 12lbs. of the best Hamburg zinc, in cakes about inch thick, which were broken into pieces.
The copper was first melted, and when the whole was nearly run down the coke was removed to expose the top of the pot,
* Twenty-four assays were made from as many bars, from 11 to 2 lbs. weight; besides which, several failures were laid aside.