In Lardner's Cyclopedia. Manufactures in Metal, Vol. III., p. 103, it states:
"The composition of Britannia metal is as follows: - 3 1/2 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 raiding 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 of the zinc 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 then, 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."
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 howsoever conducted, a considerable waste of the zinc will inevitably occur.
It is also certain that every 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 541b. of copper shot, about 101b. 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 lb. 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 lb. of copper shot, 27 lb. of sholed spelter, about 10 lb. of calcined calamine, and about 1 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 lb. of pure fine brass, fit for making ingots or casting plates for making brass battery ware, 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 while oxide of zinc; and in gnu-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 vitrreous 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 the oxidation; but the brassfouuder frequently leaves the metal entirely un-covered; 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.*