400 



INCANDESCENT MANTLES. 



having a dense central portion surrounded l)y a more or less spongy 

 coating, due to the fact that the soaked fabric on burning off leaves the 

 oxides produced from the interior of the capillaries in a dense state 

 while the salt on the exterior of the cotton in its conversion into oxide 

 bj'^ heat is rendered spongy by the escape through it of the gaseous 

 products of the combustion of the cotton, so that if a section of one of 

 the lilaments constituting a strand could be examined under the micro- 

 scope, the appearance would be somewhat as described. The physical 

 effect of this on the mantle is that the Clamond class is harder than the 

 Auer and does not show the same high incandescence until the surface 

 of the filaments has become eroded b}^ burning for a short period, the 

 life of the Clamond class when made of the same material as the Auer, 

 however, being longer. For instance, two mantles made one b}^ the 

 Plaissetty and one by the Auer method so as to 3' ield an ash containing 

 99 per cent thoria and 1 per cent ceria would give curves of the 

 following character (tig. 2), the total life of the Knoffler and Plaissetty 

 mantles being probably a third longer that of the Auer: 



80 



70 



60 



50 



100 100 300 400 



Hours iurning. — — — ^Knoffler. — 



SOO 600 



Wetsbach. 



Fig. 2. — Endurance of Welsbach and Knofller mantles compared. 



There seems every probabilit}^ that mantles of Knoffler and Plais- 

 setty tj^pe will play an important part in incandescent lighting, as in 

 Paris the Welsbach Company has acquired the patent rights of the 

 process and is introducing an innovation upon it. On taking a collo- 

 dion mantle and heating it in a drying oven for a certain length of 

 time a considerable shrinkage takes place, and if this shrunken mantle 

 is then placed on a burner and burnt off' the fabric rapidly moulds 

 itself to the form of the flame with but little manipulative aid. For 

 street lighting and for maintenance work it would manifesth' l)e a 

 great convenience to do awa}' with the collodionizing altogether, which 

 always, to a certain extent, impairs the light-giving power of the 

 mantle. 



Another new feature which has oeen introduced into mantles of this 

 class is the doing away with the asbestus thread and loop, which has 



