115

A press producing 90,000 bricks in ten hours requires an engine of thirty-five horse-power, and there are employed in mining the coal and operating the plant as many as 100 to 130 men.

Briquettes of this character are in demand for use among the farmers, and wherever a low priced fuel is needed and no great heating power required. In 1890 there were forty-five factories of this character in Germany, and the production for the year was 340,000,000 bricks, which were worth at the factory $2 per thousand.

DRY PRESSING.

The manufacture of briquettes by heavy pressure without the use of bond has, up to the present, only proved applicable to certain kinds of brown coal, and to those bituminous coals which are of a decidedly caking character, in which the heat evolved by compression causes the development of sufficient bituminous matter to cement it.

The brown coal which lends itself most readily to this method of treatment is the earthy or common brown coal which occurs in such abundance in the province of'Saxony and on the Rhine.

As it is mined the coal is a mixture of earthy or common brown coal, with more or less "schweel" or tar coal and lignite. The deposits are of great thickness, twenty and even thirty feet not being uncommon, and even much greater thickness being found. As they usually lie near the surface, they are worked by open mining. The coal is roughly separated, as mined, into that which is intended for the manufacture of tar at the schweelerie, and that which goes to the briquette press. From the mine it passes by underground or overhead channels to the place of its destination, and is there again culled before being used.

The coal as it comes from the mine is, for the most part, of an earthy, friable nature, smeary, brownish-black in color, and contains from 40 to 60 per cent of moisture. Before it is compressed the excess of water must be driven off by evaporation.

The process of dry briquetting may be divided into

• (a.) Pulverizing and mixing.
• (b.) Drying.
• (c.) Pressing.