792 



These pieces are to be riveted to the under- 

 side of the fan-case. A fiber wheel 2 in. in 

 diameter is turned in a lathe and fitted to a 

 U-shaped piece of strap iron % in. wide. 

 Now rivet the wheel-support to the under 

 side of the fan-case in such a position that 

 the wheel will support about one-half of the 

 weight, the other half resting on the shoe. 



The fan, Fig. 12, is cut out of sheet iron 

 1/32 in. thick. There are six blades, in 

 pairs. The three pieces comprising the 

 blades are to be firmly screwed to a brass 

 hub, the dimensions of which are given. 

 For added safety it is well to sweat the 

 blades to the hub with solder to 

 prevent them from becoming 

 loose. The fan is secured to the 

 shaft by means of 

 one of the screws 

 used to hold the 

 blades to the hub, 

 the screw being 1/16 

 in. longer than the 

 others for this pur- 

 pose. 



The handle is 

 about 1 in. in diame- 

 ter and 2Y2 ft. long. 

 Two pieces of strap 

 iron are bent as 

 shown and secured to 

 the handle by means 

 of two small bolts. 

 On the under side of 

 the handle a groove 

 is cut to receive the 



Popular Science Monthly 



Small electrical furnace to melt the more 

 precious metals and for experimental use 

 in making calcium carbide and carborundum 



conductor cord. A small one-point switch 

 should be mounted on the upper end 

 of the handle to control the motor. The 

 connecting cord should be 30 ft. long, so as 

 to permit of a large radius of operation 

 from one electric socket. 



The dust bag is of any closely woven 

 material, 30 by 8 in., of the shape shown. 

 On the smaller end a coiled spring is 

 sewed. This fits over the end of the exhaust 

 of the fan. The other end is closed by a 

 6-in. paper clip, the latter being supported 

 by a small coiled spring fastened to the 

 handle. 



The mechanical details of the machine 

 are now complete. The motor and handle 

 should receive two coats of black enamel, 

 and the shoe two coats of aluminum enamel. 

 If care has been exercised in the construc- 

 tion of the vacuum cleaner it will present 

 a very neat appearance and give as satis- 

 factory service as [any electrically driven 

 machine of its size. 



Making an Electric Furnace for 

 the Laboratory 



IT is often desirable to use a heat above 

 that of the ordinary bunsen burner, for 

 instance, to melt silver or gold or make 

 calcium carbide or carborundum. To do 

 this on a small scale, the electric furnace 

 herein described will be found convenient. 

 The material necessary consists of two 

 standard-size fire bricks, two %-'m. arc 

 light carbons 6 in. or more in length, and 

 four porcelain knobs for supports. 



At the center in the top of a 9 by 4^ by 

 2^-in. fire brick gouge out a hole 

 in diameter and 1 in. 

 deep with a cold chisel, then cut 

 grooves as shown at 

 A and B. These 

 should extend from 

 the surface 3^ i n - 

 from either end to 

 the hole at the cen- 

 ter, where they are 

 3^-in. deep and of 

 sufficient width to al- 

 low the carbons to 

 slide freely. 



The cover brick is 

 about 4^ by 4^ by 

 2}/2 in. This should 

 be gouged out slight- 

 ly concave at the 

 place in the bottom 

 which is over the 

 melting pot. This is 

 done to help reflect the heat into the melt- 

 ing pot. The furnace is connected with a 

 no-volt circuit through a water rheostat. 

 A water rheostat capable of keeping the 

 furnace running for an hour and a half on 

 8 amperes can be made by immersing two 

 copper strips in a vessel containing at least 

 !/^2 gal- °f water. Add enough ordinary 

 table salt to allow sufficient current to pass 

 through so an arc can be struck when the 

 carbons are touched together. Then insert 

 an ammeter in the circuit, strike an arc and 

 then add more salt until the ammeter reads 

 five or six amperes. If it is desired to run 

 the furnace for a longer period the rheostat 

 should be built accordingly. 



To make carborundum crystals, mix the 

 following: 2 parts sand; 3 parts carbon, 

 (coal or coke) ; 1 part sawdust and a little 

 common salt. Heap this mixture up 

 around the carbons in the melting pot of the 

 furnace, strike an arc and allow it to run for 

 four or five hours. — E. R. Thomas. 



