December 21, 1900.] 



SCIENCE. 



953 



oxides to produce an incandescent light, 

 and even invented a basket or mantle of 

 magnesia threads, supported in an enclosing 

 platinum mantle of small wire and large 

 mesh, which was hung below the lamp and 

 the heating flame directed down into it. 

 The threads were made from magnesia 

 which was calcined and pulverized, then 

 made plastic by mixing with salts of mag- 

 nesia, which may be aftei'wards decomposed 

 by heat, then squirted through a die, woven 

 into a basket form and dried and baked. 



In 1885, Otto B. Fahnehjelm, a Swedish 

 inventor, secured an American patent (see 

 U. S. Patent No. 312,452, February 17, 

 1885) for an incandescent light which con- 

 sisted in the combination with a suitable 

 gas burner and a shade holder of means for 

 suspending an incandescent body in the 

 flame of the burner, and for adjusting the 

 incandescing body horizontally and verti- 

 cally in relation to the flame. The Fahn- 

 ehjelm light consisted substantially of a 

 series of rods of calcined magnesia, resemb- 

 ling the teeth of a comb, held in a suitable 

 frame and suspended in a non-luminous 

 flame of gas. 



In 1886, Galopiu and Evans (in Austra- 

 lia) produced a lamp burning hydrocarbon 

 vapor mixed with air to produce a heating 

 flame, directed downwards into a woven 

 platinum mantle, which was thus made in- 

 candescent. 



About this same time, or even a little 

 earlier (1885), Carl Auer von "Welsbach 

 announced the invention of a lamp in 

 which the rare oxides of lanthanum, 

 yttrium, zirconium, etc., in a finely divided 

 condition, were rendered incandescent by 

 heating to a high temperature. The source 

 of light was a light netwoi'k of cotton 

 thread impregnated with a solution of the 

 salts of the combined nitrates, oxides or 

 bromides. After being saturated with these, 

 upon exposure to heat, the supporting cot- 

 ton network was burned out, the salts con- 



verted into the oxides and a skeleton hood 

 or cap thus prepared, which would incan- 

 desce when a heating flame was applied 

 to it. 



The absolute originality of this form of 

 mantle and method of manufacture should 

 be carefully noted. 



The nitrates of the metals, being very 

 soluble, were especially adapted to the proc- 

 ess, although sulphates, iodides or bromides 

 could also be used. 



Welsbach found that this mantle, as it 

 came to be called almost from the first, 

 could resist the action of all atmospheric air 

 fit to breathe for an indefinite length of time, 

 was not changed by exposure and would re- 

 main efi'ective for a long time. 



For the next five years or more von Wels- 

 bach was constantly at work making elab- 

 orate investigation of the properties of all 

 oxides of metals which would incandesce 

 when used . separately, and when combined 

 in various mixtures. He invented proc- 

 esses whereby the salts of the metals re- 

 quired for impregnating mantles might be 

 prepared from the natural ores, originated 

 means for strengthening the frail mantle, 

 aiTanged the mantles for transportation in 

 safety, and perfected many details making 

 the lamp practical. 



It is interesting to notice that the form 

 of mantle and the general process of man- 

 ufacture have remained up to the pres- 

 ent precisely as von Welsbach originally 

 planned them, without improvements or 

 essential modification of any kind. 



One or two of the discoveries of von 

 Welsbach are necessarily mentioned a little 

 in detail, to explain the magnitude of the 

 investigations he conducted and the sort of 

 results he procured. 



A patent ISTo. 409,531, August 20, 1889, 

 explains that the illuminating power is 

 greatly increased by adding thorium oxide ; 

 that lanthanum oxide without sufiioient 

 thorium oxide crumbles when incandes- 



