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operation. In Italy, where the brown coal is almost the only source of supply, this method of converting it into a serviceable fuel is receiving considerable attention, and in many of the factories the brown coal forms a part at least of the material briquetted.

THE BOND.

In the beginning of the briquette industry many kinds of material, both inorganic and organic, were used as bonds, but at present the organic are used almost exclusively.

Among the inorganic substances used at different times may be mentioned the clays (some of which are still in use today in preparation of certain coals for household purposes when the increase of ash is not such an important matter), silicate of soda, alum, alum shales with quick lime, lime water, etc. Many other materials were added to the inorganic bonds for the purpose of increasing the inflammability of the briquettes or to decrease the production of smoke and soot. Some of these were saltpetre, chlorate of potash, magnesia, slacked lime, potash, soda, nitric acid, hydrochloric acid, permanganate of potash, etc. None of these, however, are now in practical use, and the only substitute for pitch which is at present worthy of attention is magnesia cement.

ORGANIC BONDS.

Coal Tar.—This material was used as bond in the oldest briquette factories, but the product was not firm enough to bear long transportation, or to withstand the heat of the sun. It develops also in burning a dense black smoke and a very disagreeable odor, and although many trials were made to overcome these disadvantages by thoroughly drying the briquettes in dry kilns, the results were unsuccessful. For these reasons, coal tar is now scarcely used in its raw state, but is sometimes added to the material for the purpose of increasing its combustibility. Its real value lies in the fact that it is the material from which the pitch used can be distilled. For this purpose only the tar from bituminous coal is generally made use of, because that from brown coal, peat and bituminous shales is found more valuable in Europe as the basis of the manufacture of mineral oil and paraffine. Pitch from wood tar and petroleum might also be used, but so far has not been applied in this direction.

Coal tar is a product of the distillation of coal, by which it is separated