〈BURNING TOGETHER BRONZE.〉
The process of “burning together” is as follows:—Two portions of a large statue, which have been cast separately, are placed in a trough of sand, with their corresponding ends near to each other. A channel is made in the sand, leading through the junction of the parts to be united.
A stream of melted bronze is now allowed to run out from the furnace through the channel between the contiguous ends which it is proposed to unite. The first effect of this is to heat the ends of the two fragments. After the stream of melted metal has continued some time, the ends of those fragments themselves begin to melt. When a small quantity of each end is completely melted, the further flow of the melted metal is stopped, and as soon as the pool of melted metal connects, the two ends of the pieces to be united begins to consolidate: the whole is covered up with sand and allowed to cool gradually. When cold, the unnecessary metal is cut away, and the fragments are as perfectly united as if they had been originally cast in one piece.
The sudden consolidation, by physical force, of pounded ice or snow appears to me to arise from the first effect of the pressure producing heat, which melts a small portion into water, and brings the particles of ice or snow nearer to each other. The portion of water thus produced then, having its heat abstracted by the ice, connects the particles of the latter more firmly together by freezing.
If two flat surfaces of clear ice had a heated plate of metal put between them, two very thin layers of water would be formed between the ice and the heated plate. If the hot {446} plate were suddenly withdrawn, and the two plates of ice pressed together, they would then be frozen together. This would be equivalent to welding. In all these cases the temperature of the ice must be a very little lower than the freezing-point. The more nearly it approached that point the slower the process of freezing would be, and therefore the more transparent the ice thus formed.
〈ICE FROZEN IN THE EXHIBITION, 1862.〉
In the Exhibition of 1862 there were two different processes by which ice was produced in abundance, even in the heat of the Machinery Annex, in which they were placed.
In both the water was quickly converted into ice, and in both cases the ice was opaque.
In one of them the ice was produced in the shape of long hollow cylinders. These were quite opaque, and were piled up in stacks. The temperature of the place caused the ice to melt slowly; consequently, the interstices where the cylinders rested upon each other, received and retained a small portion of the water, which, trickling down, was detained by capillary attraction. Here it was very slowly frozen, and formed at the junction of the cylinders a thin film of transparent ice. This gradually increased as the upper cylinders of the ice melted away, and, after several hours’ exposure, I have seen clear transparent ice a quarter of an inch thick, where, at the commencement, there had not been even a trace of translucency.
On inquiring of the operator why the original cylinders were opaque, he told me, because they were frozen quickly. I then pointed out to him the small portions of transparent ice, which I have described, and asked him the cause. He immediately said, because they had been frozen slowly.