MECHANICS AND USEFUL ARTS. 47 



intensity of heat can be obtained, sufficient to melt the most refractory sub- 

 stances, without any other fuel being used than the ordinary gas used for 

 liiihting the house. The construction of the furnace is as follows : 



^Attached to a large retort-stand, by a horizontal arm, is a small metal box 

 between two and three inches in diameter. This box is divided into two 

 parts internally; the upper part being connected by a flexible tube with the 

 gas-piping of the room; the under part is in like manner connected with a 

 pair of double bellows. On the top of the metal box is fixed a burner, 

 consisting, in most instances, of sixteen jets, each of which is formed of two 

 tubes, the outermost of which is short aud only reaches into the upper part 

 of the metal box, while the inner tubes are long enough to penetrate the di- 

 vision, and to reach the lower part of the box. This burner, with its six- 

 teen tubes, forms a small flat cylinder on the top of the box, around which, 

 and fitting it exactly, is placed a large flat disk of porous earthenware, in 

 shape like a millstone, and of a thickness equal to the height of the burner. 

 Over this burner is placed a plumbago crucible with a lid, and supported by 

 a semi-globular stand of the same material, like an inverted basin, pierced 

 all over with small holes, and having a large hole in the centre to receive 

 the bottom of the crucible; over this latter is placed a second, but larger 

 cup, similarly pierced with small holes. Round the crucible, thus supported 

 and covered, is placed a large cylinder made of porous earthenware, of the 

 same diameter externally as the flat disk, and with exactly sufficient space 

 in the centre to admit the crucible, cover, etc. This cylinder has a small 

 hole in the side, through which to watch the crucible, and this hole is stopped 

 with a plug. On the top of the first cylinder any number of others may be 

 placed as required, and space between the crucible cover and the top of the 

 highest cylinder may be filled with pieces of earthenware or pebbles, and 

 the whole covered with a piece of tile. When the gas is turned on, it passes 

 at first into the upper chamber of the metal box, and thence between the 

 inner and outer tubes of the burner, where it comes into contact with the air 

 which is forced by the bellows through the long tubes; this current of air 

 produces rapid combustion of the gas, which, rushing out through the holes 

 of the stand under the crucible, entirely surrounds the latter with a most 

 ardent flame. The object of the earthenware cylinders and pebbles is solely 

 to prevent the escape of the caloric. This is effected in so perfect a manner, 

 that the hand can be placed with impunity on any part of the apparatus 

 while the inside is glowing with a white heat. 



By means of this furnace, it is stated, three pounds of copper can be 

 melted in ten minutes, at an expense of a cent and a half. 



* 

 FIRE GRATES AND CHIMNEYS. 



A commission, appointed by the Board of Health in England, consisting 

 of Mr. Fairbairn and Professors Wheatstone and Playfair, have made a re- 

 port on grates and fire-places, in which they recommend some changes. 

 They urge, for all parlor grates, the use of a greater amount of reflecting 

 surface, to direct more heat into the room, and they advise the flue of the 

 chimney to be much smaller than those in common use a reform which 

 we have also frequently advocated. They state that the flue of a chimney 

 does not require to be made more than nine inches in diameter at its widest 

 part; a narrow chimney diminishes the quantity of ascending air, and a 

 tendency to smoke. Chimneys always draw better when they are kept 



