954 



SCIENCE. 



[N. S. Vol. XII. No. 312. 



cent — with it the mantle becomes flex- 

 ible. Later he found (patent No. 563,524) 

 that thorium oxide, by the addition of a 

 small per cent, of uranium or cerium oxide, 

 has a very high illuminating power, pro- 

 ducing a vivid and neai-ly white incandes- 

 cent light, in spite of the fact that thorium 

 oxide alone radiates little light which is 

 yellow in color, and that uranium oxide 

 alone radiates little light, and it is yellow 

 reddish. Still later, he discovered that the 

 illuminating power of lanthanum, cerium, 

 yttrium, zirconium and other metals of the 

 refractory earths is greatly increased by 

 the addition of thorium oxide (ThOJ ; 

 that cerium not only gives a yellow light 

 (very desirable color), but greatly increases 

 the life of the mantle, causes it to hold its 

 shape better, and makes it in every way 

 stronger and more durable. 



Thus we get a slight idea of the elabo- 

 rate researches conducted by Dr. von Wels- 

 bach, and of the many difficulties which 

 had to be overcome before the Welsbach 

 mantle could become practical and com- 

 mercial. 



To complete the storj' of lights procured 

 by the incandescence of metallic oxides, 

 mention should be made of the lamp in- 

 vented by Professor Walther IS'ernst, of the 

 Universitj' of Gottingen, early in 1899, the 

 substance rendered incandescent being a 

 magnesia rod through which an electric 

 current is passed after preliminarj' heating. 

 Not only is this light related to the same 

 group as the Welsbach, not only does it 

 give a very modern illustration of a sort of 

 lamp mentioned earlier in the report, but 

 (most interesting of all) in his latest work 

 Nernst gives up the magnesia and uses the 

 same mixtures of oxides as used in the 

 Welsbach mantle — zirconium, thorium, 

 cerium, erbium, etc. 



A very brief description of the lamp and 

 mantle made for use with illuminating gas 

 by the Welsbach Light Company, of Glou- 



cester, N. J., will give the best idea of pres- 

 ent methods, and serve to bring out some 

 important points with refei-ence to the light- 

 giving power, durability and economy of 

 the mantle as put on the American market. 

 The Welsbach ' J ' mantles (standard until 

 verj' recently) were made about as follows : 

 A six-cord cotton thread was woven on a 

 knitting machine forming a tube of knitted 

 fabric of rather open mesh. This web has 

 the grease and dirt thoroughly washed out 

 of it, is dried, then cut into lengths double 

 that required for a single mantle. It is 

 then saturated in the fluid (described 

 later), wrung out," stretched over spools and 

 dried. Next, the double length pieces are 

 cut into two, the tops of each piece doubled 

 back and sewed with a platinum wire 

 which draws the top in and provides a 

 means of supporting the mantle when fin- 

 ished from tlie wire holder. After stretch- 

 ing the mantle over a form, smoothing it 

 down and fastening the platinum wire to the 

 wire mantle holder, the mantle is burned 

 out by touching a Bunsen burner to the 

 top. The cotton burns off slowly, leaving 

 a skeleton mantle of metallic oxides, which 

 are unconsumed, and which preserve the 

 exact shape and detail of every cotton 

 fiber. The soft oxides are then hardened 

 by a Bunsen flame. During burning out 

 and hardening, considerable shrinking 

 takes place. This finishes the process, ex- 

 cept the immersion of the mantle in crys- 

 talline, to prepare it for transportation, 

 after which it is trimmed and packed. The 

 fluid in which the cotton webbing is im- 

 mersed is procui'ed from monazite sand, 

 which yields in the finished mantle oxides 

 of thorium and cerium. 



The candle-power of mantles of the sort 

 mentioned is about 75 initial candle-power 

 under gas pressure of Philadelphia illumi- 

 nating gas. This means 20 candles per cubic 

 foot per hour (an ordinary 8-foot fish tail 

 burner gives not over three candle-power 



