138 Prof. J. Joly on a Method of Investigating the 



folded in zigzag according to a pattern as under (full size) 

 laid down on a piece of paper. The folds beneath the dotted 

 line are then bent at right angles to the paper, and the whole 

 bent round the platinum crucible and pressed against its 

 surface. This gives it the right set. This basket is placed 

 in the porcelain crucible, resting on a layer of magnesia. 



Fig. 2. 

 to 



fc\ fr^ 



\& 



& 



^\ r? 



\y> 



A little more magnesia is then added and the platinum 

 crucible placed in position. Magnesia is next poured in 

 around it and shaken down. The heater should be as close 

 to the platinum as possible. This furnace is simple and 

 effective, giving temperatures up to 1200°. The higher tem- 

 peratures are, however, only got at the risk of shortening the 

 life of the resistance wire. It would, doubtless, be better to 

 imbed the wire in compressed magnesia, but this is not easy 

 to effect without special appliances. The system of vertical 

 folding is adopted chiefly for the reasons that it is easy 

 thereby to distribute the heat as required, and that it is not 

 attended by the gradual sagging downwards, which occurs 

 when the wire is spirally folded and left unsupported by a 

 rigid material. 



It is desirable to watch the progress of the fusion lest there 

 be risk of boiling over. For this purpose a small opening is 

 made in the reflecting cover of platinum. The opening is to 

 one side. The gases escaping from the furnace pass first 

 into a small bulb to catch and hold back a certain amount of 



