Page:Popular Science Monthly Volume 23.djvu/827

This page has been proofread, but needs to be validated.

in large quantities in France and Spain. In the cheaper kinds of chocolate and cocoa, these husks are ground with the nibs, and some other cheap farinaceous substance is added. The black appearance of such chocolate is unmistakable; it will always be found gritty and rough, and, of course, difficult of digestion. The husks are no better than sawdust, and may cause irritation by the minute spiculæ left after grinding.

I must now touch upon the utilization of mineral waste.

The utilizing of tin-plate cuttings and the recovery of the tin have become important and profitable industries. In the manufacture of tin-ware, it is said six per cent of the whole of the plates employed disappears in the form of scrap. Birmingham produces thirty tons per week. Mr. Beck, of that town, is said to have made a profit for many years of £100 a week by taking off the tin from the scrap by solution and precipitation. A very fair trade is done by parties who go about the tin-works buying up the tin-dust. They even go to France and other countries, and ship it to England to be reduced. This so-called tin-dust is really the scum of the tin-pot, and, as it is mixed with grease, it is black. It contains a considerable quantity of metal, which is reduced by ignition and flux. An engineering paper States that the waste of tinned iron, used for all kinds of purposes, but especially for saucepans, kettles, button-making, etc., was formerly large, but a method is now employed by which the tin can be recovered from the waste, simply by the action of dilute sulphuric acid. Tin, to the extent of from five to fifteen per cent, and worth about §97 per ton, with a vast amount of sulphate of iron, is thus procured, giving a large profit on the operation.

Within the last quarter of a century, that formerly neglected mineral—pyrites—has been turned to useful purposes, to supply our manufacturers with the important material, sulphur.

In wire-making factories, the dilute sulphuric acid, formerly used to clean the wire, was allowed to run into the sewer, when it had become so charged with the iron scale as to cease to "bite," and large quantities of refuse wire were employed only to fill up hollows in grading, or thrown into a heap. All this waste material is now r, however, converted into articles of commercial value. The processes are simple and comparatively inexpensive.

Not only in the inferior metals is waste now prevented, but increased attention is given to the collection of gold formerly lost. Immense heaps of refuse, or "tailings," as they are technically termed, accumulate where mining operations are carried on. The sludge which is emptied from the puddling-mills in Australia contains a considerable quantity of fine gold. Much of this is now recovered, and the yield of gold from it exceeds three pennyweights per ton. The right to wash the tailings is often sold to the Chinese, who are always well satisfied with the result of their labors.