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 every 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 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.
* The loss which occurs in molting 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 he only removed by the hammer and cold-chisel.
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 the so-called copper castings, about 4 oz. of brass are added to every 2 or 3 lb. of copper. And in ordinary work, a pot of brass weighing 40 lb., is made up of 10, 20, or 30 lb. 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, 24 lb. of copper to 12 lb. 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 every time, in order to ascertain the average loss of zinc in every 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 addition of zinc. And lastly, to have the whole of the bars assayed, to determine the absolute proportions of copper and zinc contained in all, 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 melted alone to ascertain the loss sustained by passing through the fire, which was found to be barely 1/4 oz. on the whole. A similar weight of the same copper was weighed out, and also 12 lb. of the best Hamburg zinc, in cakes about 3/4 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, which was watched until the boiling of the copper, arising probably from the escape of bubbles of air locked up at the lower part of the semi-fluid mass, ceased, and the copper assumed a bright red, but sluggish appearance; the zinc was then added.
* Twenty-four assays were made from as many bare, from 1 1/2 to 2 lbs. weight; besides which, several failures were laid aside.
Precaution is necessary in introducing the first quantity of zinc, not to set the copper, which is liable to occur if a large quantity of cold metal is thrown in, simply from the abstraction of beat; and it is also necessary to warm the zinc that it may be perfectly dry, as the least moisture would drive the metal out of the pot with dangerous violence. A small lump of the zinc, therefore was taken in the tongs, held beside the pot for a few moments, and then put in with the tongs with an action between a stir and a plunge, regardless of the flare, and of the low crackling noise, just as if butter had been thrown in; the zinc was absorbed, and the surface of the pot was clear from its fumes almost immediately. The remainder of the zinc was then directly added, in about eight pieces, one at a time, much in the same manner, but the danger of setting the copper nearly ceases when a small quantity of the spelter is introduced. After every addi-tion the pot was free from flame in a few moments, a handful of broken glass was then thrown in, the tile replaced, and the whole allowed to stand for about fifteen minutes to raise the metal to the proper heat for pouring, which is denoted by the commencement of the blue fumes of the zinc.
The pot was then taken from the fire, well stirred for one minute and poured; the weight of the brass yielded was 34 lb. 12 1/2 oz., showing a loss of 1 lb. 3 1/2 oz., or one-tenth of the zinc, or the one-thirtieth part of the whole quantity. This experiment was repeated, and the loss was then 1 lb. 3 oz., the difference being only 1/2 an oz. By analysis, the mean of the two brasses was 31 1/4 per cent. zinc; or instead of being 8 oz. to the pound, it was only 7 1/4 oz.
Twelve pounds of each of these experimental mixtures were remelted six times, a bar weighing about one pound and a half, bring taken every time; the two series of trials were conducted in different foundries, by different men, and quite in the ordinary course of work; but the loss per cent. of zinc was in the six experiments exactly alike in each series, that is, each bar, after the sixth melting, contained 22 1/2 per cent. or 4 5/8 oz. to the pound of copper. The second fusion in each case sustained the greatest loss, (say nearly two-fold); and in the others, taking all the accidental circumstances into account, the loss might be pronounced nearly alike every fusion.*
In making the alloys with more zinc, the calculated weight of the first alloy was melted, and the amount of zinc was warmed and plunged in with the tongs, whilst the pot was in the fire, the whole was stirred and quickly poured: the losses in weight were rather large, but this is common when the zinc is in great quantity. To make the alloys containing less zinc than the alloy, the calculated weight of copper was first made red-hot and the respective portion of the brass alloy was then put in the pot, by which means the two ran down nearly together: it being found that the copper, if entirely melted before the brass was added, incurred a risk of being set at the bottom of the pot; and remelting the mass, wasted the zinc. These alloys came out much nearer to their intended weights.
In making the tin and copper alloys, very little difficulty was experienced. The copper was put into the pot together with a little charcoal, which was added to assist the fusion and also to cause the alloy to run clean out; as in pouring gun-metal a small quantity is usually left on the lip of the crucible, which would have been an interference in these experiments. When the copper had ceased boiling, and was at a bright red heat, it was taken from the fire, and the tin previously melted in a ladle, was thrown in, every mixture was well stirred and poured immediately.
In the fourteen alloys thus formed, each weighing about a pound and a half, namely, 1/2, 1, 1 1/2, etc, up to 8 oz. of tin to the pound of copper, (missing the 6 1/2 and 7 1/2,) no material loss was sustained in nine instances, and in the other five it never exceeded 1/8 oz. and that quantity was probably lost rather in fragments than by oxidation.
Alloys of 2, 4, 6 and 8 ounces of lead to the pound of copper, were made exactly under the same circumstances as the last.
* Lord Oxmantown required the proportion of 2.75 copper and 1 zinc, to be very carefully preserved, as that alloy was found to expand equally with the speculum metal to which it had to be soldered. After many trials, Lord Oxmantown found that by employing a furnace deeper than usual, and by covering the metal with a layer of charcoal powder two inches thick, the loss every time was the smallest, and almost exactly the 180th each casting. To renew the charcoal dust it was folded up in paper and tin-own in. See Trans. Royal Society, 1840, p. 607