Page:Popular Science Monthly Volume 92.djvu/325

 Popular Science Monthly

��309

��How to Make an Electric Laboratory Furnace

IN the laboratory, it is often desirable to secure heat greater than that pro- duced by the Bunsen burner, or even a greater range of temperature than can

���Flower pot susi>ended on a ring stand and holding crucible to melt metals electrically

be reached by the Scimatco burner. This makes the use of an electric furnace necessary. A furnace that can be con- structed by any amateur is herein de- scribed. It is very convenient to handle, and the materials that are utilized in it, can for the most part be found in the laboratory. The terrific heat generated by this furnace is capable of reducing alumina. Its other uses are familiar to all those who work in the laboratory.

As can be ascertained in the accom- panying illustration, one of the most essential parts of the apparatus is the two-ring stand which serves as a support for the main part of the furnace. The rings support a flower pot, in which ia placed a small crucible, made either of porcelain or alundum, according to the work that is to be done by the electric furnace. The crucible should be placed in the flower pot in such a manner that it may be readily removable when neces- sity arises. The space between the flower pot and the crucible is filled with pulverized fire-brick, but if that cannot be obtained, the fire-brick may be of the ordinary granulated variety, A sheet of thick mica covers the top of the fur- nace, and a hole is bored in it to permit the passage of the carbon. This carbon is supported by the upper ring which has been provided with an asbestos plug

��to hold the carbon stationary. A brass ring prevents the carbon from slipping, and forms a means of regulating the distance between the carbons. The other carbon goes through the bottom of the flower pot, and through the crucible, which has previously had a hole that fits the carbon snugly drilled in its bottom. The lower carbon rests upon a block of wood or asbestos which is placed on the base of the stand. The terminals of the furnace are shown in the illustra- tion. To secure best results, the lead-in wires should be of No. 14 copper wire. The furnace requires from six to eight amperes of current, using a direct or alternating current of 110 volts con- nected with incandescent lamps as shown, or with a water rheostat. At first, it is advisable to operate the furnace empty, in order to ascertain whether the appa- ratus stands up well under the terrific heat generated. It is also strongly ad- vised that the operator use smoked glasses when the furnace is in play, as the glare produced has an unpleasant effect on the eyes. — Herman Neuhaus.

��Thermostat Made from a Brass and an Iron Strip

IRON and brass expand to different lengths at the same temperature and for this reason these metals are ideal for

���The two metals riveted together and mounted on a base to operate an electrical system

making a thermostat. I took a piece of iron 12 in. long, }4 in- wide, and 1/16 in. thick and riveted it to a similarly shaped strip of brass. This compound strip I

�� �