KNOWLEDGE. 



Jri.v. 1911. 



■■ Thermit " is also employed technologically as a butt-welding of iron pipes. The ends of the 

 heating agent. As Dr. Goldschmidt has pointed out,* pipes to be welded together are surrounded bv 

 in ■■ thermit" we have a new sort of fire differing a suitable luould. into which the products of the 

 in certain respects from all 

 other fires. In the first 

 place, in the combustion 

 of "thermit "' neither is air 

 consumed nor is anv gas 

 evolved, as in the case of 

 the combustion of such 

 substances as wood, coal, 

 coal-gas or petrol. The 

 second difference is in the 

 heat densitv. The actual 

 amount of heat obtainable 

 from a given weight of 

 "thermit" is realh" much 

 less than that obtainable b\ 

 the combustion of the same 

 weight of anthracite: but in 

 the former case the \\hole 

 of this heat is, so to 

 speak, obtained at once, 

 the reaction between large 

 quantities of iron oxide 

 and aluminium, as we 

 ha\e already indicated, 

 occupying a \ery short 

 period of time : indeed, b\- 

 the combustion of "ther- 

 mit " a heat density is 

 pr(_)duced unattainable 

 otherwise. It is these 



peculiarities m its behaviour which determine the to heat the lines to welding point, but the liquid 

 apphcaliihtx- of the " thermit " fire. Where a steel produced is emploved to form a bulb of metal 

 continuous heating effect rather than density of heat is holding the two lines together, thereby strengthening 



the joint. An 



Figure 4. 

 Aluiiiino-therniic weldint; of train rails. 



■■ thermit '" reaction are 

 poured. Welding tempera- 

 ture being reached, the 

 ends of the pipes are 

 pressed together bv means 

 of screws arranged in 

 position beforehand. Of 

 course, if the liquid iron 

 jiroduced in the reaction 

 were allowed to come into 

 contact with the pipes. 

 the\" would be burnt 

 through, but it is found, 

 as a matter of fact, that 

 the highh-refractory alu- 

 mina slag, which issues 

 from the crucible first on 

 pouring out its contents 

 after the reaction, solidifies 

 on the surfaces of the 

 pipes, thus forming a 

 protective coating which is 

 impenetrable b\' the molten 

 metal. 



In a method of welding 

 which has been chiefl\- 

 applied in the welding of 

 tram lines, not onl\- is the 

 heat deri\-ed from the 

 "thermit" re-action utilised 



the essential de- 

 sideratum, "ther- 

 mit" would be 

 useless: thus it is 

 not suitable as a 

 source of heat for 

 locomotive pur- 

 poses or for cooking 

 generally. But 

 where great density 

 of heat is required, 

 " thermit " is pre- 

 ferable to other 

 forms of fire, be- 

 cause by its aid one 

 can so readily pro- 

 duce an enormou> 

 tem{)erature at a 

 moment's notice. 



One of its chief 

 applications as a 

 h e a t i n 



dv 



!S 



agent 

 in t h e 



-Aliunino-thennic welding 



Figure 5. 

 )f ''third" rails iParis, Metropolitan Raihvayl. 



illustration of the 

 method in use is 

 shown in Figure 4. 

 The " thermit " is 

 ignited in a crucible 

 with a hole in the 

 bottom fitted with 

 a device for tap- 

 ping. The moulds 

 around the rails 

 are constructed in 

 such a manner 

 that the "thermit" 

 steel, which fir^t 

 issues fro m t h e 

 crucible when it is 

 tapped after the 

 re-action is o\-er, 

 r u n s to the 

 bottom, forming a 

 metal bulb over 

 the joint to al)out 



H. Goldschmidt: " .Alumino-Thennics.- Transactions of the American Elcctruchcinical Society 119041. \'ol. \'I, 



Part II, pp. S5 et seq. 



