State Agricultural Society. 295 



wall of brick, inclosed in a shell of boiler-iron. The charging appara- 

 tus is also borrowed from blast furnace construction, and is of the kind 

 called Parry's bell and hopper. The mouth of a conical hopper is closed 

 by drawing up into it an upright suspended cone. When the hopper is 

 filled the cone is lowered, and the ore enters the furnace, but its fall is 

 broken by the presence of the cone, and it is thus necessarily distrib- 

 uted in all directions in the furnace. The cone is instantly raised again, 

 and thus shuts off the escape of gas. 



THE CONDENSER 



Of a quicksilver roasting furnace forms, of course, an exceedingly im- 

 portant portion of the structure, and no absolutely satisfactory construc- 

 tion has thus far been hit upon. Brick is an exceedingly porous mate- 

 rial, and quicksilver both filters through it and is absorbed into it by the 

 almost resistless force of capillary attraction. Some years ago, in pull- 

 ing down an old furnace at New Almaden, it was found that the metal 

 had penetrated the foundation and the earth for over thirty feet, and 

 down to the bed-rock. Since then the furnaces have been built on 

 arches, and in the pillars, on which the arches rest, sheet iron plates 

 have been placed to intercept the metal in its downward course; much 

 metal, however, undoubtedly penetrates the outer walls of the con- 

 denser, and is evaporated from the surface, for mercury evaporates, more 

 or less, at all temperatures above the freezing point of water, and the 

 condensers, though built of a very considerable thickness, are, of course, 

 somewhat warm on the outside. On the other hand, the thicker the 

 condensers, the less does the vapor inside cool; and, as it must cool to 

 condense, the necessity for thick walls renders a large number of con- 

 densing chambers indispensable. It is natural, therefore, to seek some 

 material better adapted to the work required than brick. Cast iron and 

 wrought iron answer very well for condensers, so long as the gas is hot, 

 but when the temperature falls below the boiling point of water, a very 

 disagreeable action sets in. Sulphurous acid, heated with air in contact 

 with highly porous substances, is partially converted into sulphuric acid; 

 this condenses with the water and attacks and soon destroys the iron. 

 Wood withstands this action tolerably well, and does not let quicksilver 

 through like brick, and it has, consequently, been much used for the 

 later condensers of the series; but wood is a non-conductor of heat, and 

 hence, properly speaking, ill adapted for cooling apparatus. At New 

 Almaden glass is found to answer excellently, being a much better con- 

 ductor of heat than wood, though not so good a one as iron, and being, 

 of course, quite unaffected by the acid liquors. The condensers assume a 

 great variety of forms, sueh as chambers of various shapes and tubes. 

 Columns of coke are also used with some success as a final conductor. 

 The draught is sometimes kept up by the aid of a chimney, with or 

 without the help of a fire, to give the air in the stack additional buoy- 

 ancy, and sometimes by a suction fan, or a "water drum," an apparatus 

 which sucks in air by means of the friction of a jet of water. So far as 

 the condensation is concerned, an artificial blast would be preferable, 

 but the danger of blowing jets of the metallic vapor through fine cracks 

 in the apparatus, would be too great to admit of its employment. 



THE LOSSES IN QUICKSILVER SMELTING 



Are various and very important, though they are not all very well 



