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 vnth 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 



