INCANDESCENT MANTLES. 399 



less than one-hundredth of a millimeter, this enormous pressure 

 being required to cause the material to flow evenl}^ through the exces- 

 sively small apertures. The filaments of from ten to twelve of these 

 tubes are then twisted and wound on to a bobbin in a machine of the 

 same character as used for the spinning of silk fiber. The air of the 

 room in which this operation is carried out is kept at a sufficiently 

 hi oh temperature to cause the instantaneous setting of the filaments 

 owing to the evaporation of the alcohol and ether, so that within 3 or 

 4 inches of the tube from which the material is issuing it has lost all 

 stickiness and may be twisted without cohesion between the threads. 

 These threads have all the appearance of silk, but have one serious 

 drawback, that being practically a low form of gun cotton, they are 

 excessively inflammable and burn with a violence only a little removed 

 from that of true gun cotton. In order to overcome this trouble, the 

 skeins of artificial silk are soaked in amnionic sulphide, which has 

 the ert'ect of what is termed '' denitrating'' them and converting them 

 once more into cellulose, so that after washing and drying the mate- 

 rial is not more inflammable than an ordinary fabric. This material 

 is capable of taking every .shade that the dyer's art can impart to it 

 and foi-ms a most beautiful and wonderful imitation of silk, lacking 

 only to a slight degree the elasticity found in the original article. 



This extremely beautiful process was brought to perfection bj- 

 Chardonet and protected by him during the period which extended 

 between 1886 and 1893, and in 1894 De Mare took out a patent for 

 making incandescent filaments by charging collodion with metallic salts 

 and oxides, squeezing into threads, weaving, and burning. In this 

 patent, however, he makes no mention of denitrating the collodion 

 filaments before burning, which would make it extremel}' difficult to 

 make a mantle according to his patent. 



In 1895 Knoffler patented the manufacture and denitration of collo- 

 dion threads or filaments loaded with oxides or salts, and in his first 

 claim mentions that the filaments may be "individual or spun and 

 eventually wrought or woven threads which are made after the manner 

 of the so-called artificial silk." 



Latej- on Plaissetty took out a patent which differs from Knofiler's 

 only in that he uses glacial acetic acid as the solvent for his collodion 

 cotton, and instead of denitrating with ammonic sulphide, uses a solu- 

 tion of sulphide of lime, which, however, has the drawback of leaving 

 a trace of lime as an impurity in the finished mantle. 



Mantles made by such methods as those devised by Knofiier and 

 Plaissetty are developments of the Clamond hood and not of the Aucr 

 mantle, the difference being that whereas the Clamond class consists 

 of filaments of even density made by squeezing a plastic material 

 into rods or threads which, after the binding material is burned off, 

 leave a uniform mass of oxide, the Auer class consists of filaments 



