OCTOBER, 1952 0
THERMITE IGNITION ASSURED CLYDE P. BROCKETT University of Toronto, Toronto, Canada
THE COMFORTABLE, safe, and surefire time fuse for the thermite reaction described in this journal by 0. C. Kleinl leaves nothing to be desired by anyone who places a premium on reliability in demonstrating it to lecture or laboratory groups. On the numerous occasions I have used this means to initiate the reaction, it has never failed to respond exactly as intended. This ingenious arrangement, however, is not always able, even with the igniter mentioned, to ignite some commercial grades of thermite which are so coarse as to he merely puffed away from the site of the flash without being set off. In order to guarantee t,he ignition of snch thermite, it is well to emphasize t.hat a good intermediate igniter is essential. For this purpose an intimate mixture of equal volumes of finely powdered aluminum and red oxide of iron, FezOa, both readily available from the stockroom shelf, has been found excellent, no failure having been experienced with it in long use. It is suggested, therefore, that anyone who desires a
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KLEIN,0.C., "An Improved Method for Igniting Therrnite Reaet.ions," J. CEIEM.E ~ u c . ,14, 320 (1937).
trouble-free demonstration of the thermite reaction prepare it as follows: into a crater in the thermite pour a few spoonfuls of this intermediate igniter mixt,ure, crowding it about somewhat with the surrounding thermite; and into a smaller crater in this intermediate igniter pour the Ba07aluminum powder mixture, followed up with the potassium permanganate and the drop of glycerine exactly as previously recommended'. The whole chain react,ion, onre st,arted, is explosively rapid. The demonstration now becomes one to be shown with confidence, not with misgivings about misfire. Be sure to stand well away, once the glycerine is added; and it may be just as well to have the front row in the lecture room vacated, lest someone he humed by the flying globules of molten iron. If the Ba02-aluminum powder igniter is not purchasable, thoroughly stir together approximately equal volumes of t,he two powdered ingredients, guarding against chance sparks or flame getting at it. For the sake of added safety, it is better to use a very long stirring rod and to prepare only a few grams of t,he mixture a t a time, as needed.
