MECHANICS AND USEFUL ARTS. 15 



fuel and atmospheric air, at the same time connecting the other 

 regenerator with the chimney for taking off the products of com- 

 bustion. The entire current of gases through the furnace is thus 

 reversed. The cold air from the atmosphere, and the compara- 

 tively cold gases from the producer, in passing over bricks of 

 gradually increasing temperature, as they approach the furnace, 

 become intensely heated, and, when they are mixed in the furnace 

 itself, enter into combustion under the most favorable circumstances 

 for the production of an intense heat. The principle of this so- 

 called regeneration of heat, therefore, consists in storing up the 

 waste heat in one set of fire-bricks, and afterward making use of 

 that heat for elevating the temperature of the fresh gases intro- 

 duced for combustion. The action of these regenerators is so per- 

 fect that, with a temperature of somewhat about 4,000 in the fur- 

 nace, there is no more than about 300 to be felt at the base of the 

 chimney ; the escaping gases having a temperature no greater than 

 is absolutely required for maintaining the draft. 



This is the present state of this beautiful and important inven- 

 tion. It has supplied us with the power of maintaining an exactly 

 regulated temperature in a furnace of any required size and 

 shape ; it has made us practically independent of the quality and 

 nature of the fuel used for producing the required heat from the 

 most moderate up to the very highest temperature. It has re- 

 duced the expenditure for fuel to a very great extent, and it has 

 given us one of the greatest desiderata in so many metallurgical 

 operations, namely, a dean furnace, free from ashes, dust and dirt, 

 and perfectly suitable for the working of the more refined and 

 purified materials which modern industry has produced, and is 

 still constantly improving upon. We have further to name, as an 

 important feature of the Siemens furnace, the possibility afforded 

 by it of changing the nature of the flame at will, by altering the 

 relative proportion of air and gas admitted through the flues. A 

 surplus of oxygen in the mixture will produce an oxidizing 

 flame, arid will give all the corresponding effects upon the ma- 

 terials exposed to its action. By the admission of a surplus 

 of gas, on the contrary, the flame can be made of a reduc- 

 tive character, and used accordingly for deoxidation. In metal- 

 lurgy, and particularly in the treatment of iron and steel, this 

 is of the utmost importance. There are already several new 

 modes of manufacturing steel direct from the pig iron, patented 

 and practically carried out in France and in Germany, wherein 

 the Siemens furnace is made use of as an indispensable condition 

 for their success. The Exhibition contains a collection of samples 

 of very fine steel made by M. Berard's process. This is called 

 " Acier a gaz," and is made in a Siemens furnace, direct from pig 

 iron. M. Berard constructs a Siemens furnace with the bottom 

 formed into two separate parts, each hollowed out like a dish, and 

 with a bridge between them, upon which the pigs introduced into 

 the furnace receive a preliminary heating. The flame is main- 

 tained with a surplus of oxygen, and a quantity of pig iron is 

 melted in one of the chambers or dishes. The oxidizing action 

 ojf the flame decarburizes and refines the pig iron, and after a 



