502 Sir W. Roberts- Austen [Feb. 22, 



at the same time a fungoid-like growth of alumina forms on its 

 surface (see Fig. 1). Aluminium foil will burn readily in oxygen if 

 its combustion be started by a glowing fragment of charcoal. The 

 temperature at which aluminium will abstract oxygen from a metallic 

 oxide will depend on the oxide submitted to its action. Three cases 

 may be taken : (1) Lead oxide and granulated aluminium may be 

 ignited by a match, as may also silver oxide (Ag 2 0), for it parts with 

 its oxygen very readily. (2) Chromium oxide (Cr 2 U 3 ) and granulated 

 aluminium burns slowly and requires rather a high temperature to 

 start the reaction. Oxide of iron (Fe 2 3 ) and granulated aluminium 

 also requires the presence of a readily reducible oxide to start the 

 reaction. On the other hand (3) a mixture of sodium peroxide, 

 carbide of calcium and granulated aluminium may be started by a 

 drop of water by the mere inflammation of the acetylene. In all 

 these cases, or in any other case, the products are solid, for if any 

 of the reduced metal is volatilised it soon condenses, and may be 

 collected, usually in an oxidised form. 



A B 



woo o o Ij 



V O O O 



o o o o oi 



.4OOO0| 



|0O ooo< 



Fig. 2. — Crucible in which the reduction of metallic oxides is 

 effected. A, diagrammatic section of the perforated sheet-iron 

 crucible B, lined with magnesia ; c is the mixture of aluminium 

 and the metallic oxide to be reduced to metal ; a is a piece of 

 magnesium ribbon placed in a mixture b, of aluminium and 

 some readily reducible oxide. 



In using aluminium as fuel the object, of course, is to produce 

 intense heat, and, returning to this mass of iron ore from the Surrey 

 heath, it may at once be stated that an oxide of iron, ferric oxide, is 

 the most convenient oxide to use, partly because it is inexpensive. 



Many of my audience already know that the recent investigations 

 having for their object the use of aluminium as a source of heat have 

 been conducted by Dr. Hans Goldschmidt, of Essen, and it is through 

 his labours that metallurgy enters upon an entirely new phase. It 

 would be difficult to oiler him fuller or more unstinted praise than 

 that. You will, I trust, soon realise how much this branch of metal- 

 lurgical industry is indebted to him. In its simplest form his process 

 consists in igniting a mixture of oxide of iron, ferric oxide and finely 

 divided aluminium. To this mixture the name of " thermit " has been 

 given, and several varieties of it, adapted to various kinds of work, 

 are used by Dr. Goldschmidt at the works of the Allgemeine Thermit- 

 Gesellscbaft at Essen-Euhr. 



The mixture is placed inside a crucible (Fig. 2) and is ignited by 



