THE SAVINGS OF SCIENCE. 807 



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 spicuke 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 recov- 

 ered 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 min- 

 eral pyrites has been turned to useful purposes, to supply our manu- 

 facturers 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 be- 

 come 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 , how- 

 ever, converted into articles of commercial value. The processes are 

 simple and comparatively inexpensive. 



Not only in the inferior metals is waste now prevented, but in- 

 creased 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 consider- 

 able 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. 



