LUMINOSITY OF FLAMES 277 



in the mantle. In this state the mantle is in the same resistant 

 condition as when it is finally used upon the burners, but for 

 purposes of transport it is coated with a varnish consisting of 

 nitro- cellulose and various oils, to modify the too rapid character 

 of the combustion of the nitro-cellulose. The mantles are dipped, 

 usually from 40-60 at a time, in this " collodion " solution, 

 allowed to drain and dried in ovens heated by high pressure 

 steam (Fig. 74). They are then able to withstand the handling 

 necessary for examination, cutting to length, and testing to size 

 and for minute holes, due to traces ,of silica adhering to the 

 original yarn. 



The perfect mantles are packed each one in a box having -a 

 pad of cotton wool at either end. A dozen such mantles are 

 packed into an " outer " for the shopkeeper. 



In the case of the inverted mantles, these are impregnated 

 after being cut into suitable lengths and are dried upon glass 

 forms. They are then mounted upon rings with an asbestos 

 thread, and the other end of the stocking is drawn together by 

 hand or by machines, and darned with a thread impregnated 

 with the same solution as that in the body of the mantle (Fig. 75). 

 The fixing fluid is then sprayed on to that portion of the mantle 

 which is adjacent to the magnesia ring in order to give it extra 

 strength at this point. It is then ready for burning, which is 

 conducted in the same way as with the upright mantles, except 

 that the magnesia ring is supported during burning in an iron 

 ring. Ten or twelve of these make up a tray, which goes into the 

 burning and seasoning machines. In the burning off operations 

 the eyes of the workers require to be protected from the glare by 

 the use of shades or blue spectacles. 



The inverted mantles are dipped in collodion, dried, tested to 

 see that they are perfect and that they fit the burners properly, 

 and packed into units and dozens for sale. 



The machines for the testing of the yarn consist of three parts. 



The first, upon which 500 metres exactly of the thread is 

 wound off from the cones upon which it is delivered into a skein, 

 which is then weighed upon the second part. This records 

 directly the " count " of the yarn. The other machine is a 

 stretching and strain-testing machine, which determines the 

 breaking strain of the yarn measured against a weighted bob, 

 which moves over the graduated arc. The breaking p^ain of 

 2-25 ramie thread should be from 7 to 9 Ibs. 



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