The applications of chemistry in the commercial world have been in recent years so numerous and varied that it is not possible to do more than to refer to its uses in the manufacture of soda and potash, of alcohol, ether, chloroform, and ammonia, in soap making, washing compounds and tanning, the production of gelatine, the refining of cotton seed and other oils, the art of oxidizing oils for the manufacture of linoleum and oil cloth, the manufacture of fertilizers, white lead and other paints, the preparation of proprietary medicines, of soda water and photographic chemicals, the manufacture of salt and preserving compounds, in the fermentation of liquors and brewing of beer, the preparation of cements and street pavements, the manufacture of gas, and the embalming of the dead. The most interesting and, in many respects, the most important, development of the last twenty-five years has been in _electro-chemistry_. Electro-chemical methods are now employed for the production of a large number of elements, such as the alkali and alkaline earth metals, copper, zinc, aluminum, chromium, manganese, the halogens, phosphorus, hydrogen, oxygen, and ozone; various chemicals, including the mineral acids, hydrates, chlorates, hypochlorites, chromates, permanganates, disinfectants, alkaloids, coal tar dyes, and various carbon compounds; white lead and other pigments; varnish; in bleaching, dyeing, tanning; in extracting grease from wool; in purifying water, sewerage, sugar solutions, and alcoholic beverages. The present low price of _aluminum_, reduced from $12 per pound in 1878 to 33 cents now, is due to its production by electrical methods. Among the earliest successful processes is that described in patents to Cowles and Cowles, No. 319,795, June 9, 1885, and No. 324,658, August 18, 1885, in which a mixture of alumina, carbon and copper is heated to incandescence by the passage of a current, the reduced aluminum alloying with the copper. This has now been superseded by the Hall process (Pat. No. 400,766, April 2, 1889), in which alumina, dissolved in fused cryolite, is electrolytically decomposed. Practically all the copper now produced, except that from Lake Superior, is refined electrolytically by substantially the method of Farmer’s patent (Pat. No. 322,170, July 14, 1885). All metallic sodium and potassium are now obtained by electrolysis of fused hydroxides or chlorides (Pats. No. 452,030, May 12, 1891, to Castner, and No. 541,465, June 25, 1895, to Vautin). The production of caustic soda, sodium carbonate, and chlorine by the electrolysis of brine, is carried on upon a large scale, and will probably supersede all other methods. Nolf’s process (Pat. No. 271,906, Feb. 6, 1883), and Caster’s (No. 528,322, Oct. 30, 1894), employ a receiving body or cathode of mercury, alternately brought in contact with the brine undergoing decomposition, and with water to oxidize the contained sodium. _Carborundum_, or silicide of carbon, is largely