Febbuary 4, 1910] 



SCIENCE 



163 



which is still going on. The Welsbach 

 mantle practically substitutes for the car- 

 bon of the simple gas flame another solid 

 in a finely divided shape capable of giving 

 more efficient light. This allows all of the 

 carbon of the gas to contribute to the pro- 

 duction of a hotter flame. But more inter- 

 esting than the mechanical success, to my 

 mind, is the unforeseen or scientifically 

 iinexpected discovery of the effect of chem- 

 ical composition. By experiment it was 

 discovered that the intensity and color of 

 the various mixtures of difficultly fusible 

 oxides at incandescence varied over a wide 

 range. Thus a broad field for unforeseen 

 investigation was opened. The samples of 

 Welsbach mantles which you see before you 

 were kindly loaned to me by Mr. H. S. 

 Miner, of the Welsbach Company, and 

 beautifully illustrate the application of 

 advanced chemical work to this industry. 

 The color and intensity of the light vary 

 in an unexplained manner with slight dif- 

 ferences in composition of the mantle. The 

 following are the composition and candle 

 powers of the mantles shown: 



CANDLE POWER OF MANTLES, BANGING FROM 

 PUBE TIIOKIA TO 10 PER CENT. CERIA 



Per Cent. Per Cent. Candle 



No. Thoria Ceria Power 



367 100.00 0.00 7 



368 99.75 0.25 56 



369 99.50 0.50 77 



370 99.25 0.75 85 



371 99.00 1.00 88 



372 98.50 1.50 79 



373 98.00 2.00 75 



374 97.00 3.00 65 



375 95.00 5.00 44 



376 90.00 10.00 20 



69 La, Zr, Ce Oxides, 30 



The methods of making present mantles 

 were also a part of Dr. Auer's contribution 

 to the art. Suitably woven fabrics are 

 dipped into solutions of the rare earth 

 salts; these are dried and the organic mat- 



ter burned out, leaving a structure of the 

 metal oxides. 



The pure thoria gives a relatively poor 

 light. The addition of the ceria, up to a 

 certain amount, increases the light. This 

 added component is called the "excitant,"- 

 and as the cause for this beneficial action 

 of the excitant is not known, it is possible 

 that further discoveries along this line will 

 yet be made. There is hardly a prettier 

 field for chemical speculation than is dis- 

 closed by the data on these light efficien- 

 cies. For some unknown reason, the 

 change in composition by as little as one 

 per cent, varies the luminosity over ten- 

 fold, and yet more than one per cent, of 

 the excitant (ceria) reduces the light. 

 Besides the temptation to speculation, such 

 disclosures of nature encourage us to put 

 greater trust in the value of new experi- 

 ments, even when accumulated knowledge 

 does not yield a blazed trail for the pioneer. 

 By giving a discovery a name and attach- 

 ing to it a mind-quieting theory, we are 

 apt to close avenues of advance. Calling 

 this small amount of ceria an "excitant" 

 and guessing how it operates is directly 

 harmful unless our guess suggests trial of 

 other substances. 



One of the explanations proposed to 

 cover the action of the ceria ought to be 

 mentioned, because it involves catalysis. 

 This is a term without which no chemical 

 lecture is complete. Some think that the 

 special mantle mixture causes a more rapid 

 and localized combustion, and therefore 

 higher temperature, by condensation of gas 

 in its material. Others think that this par- 

 ticular mixture permits of especially easy 

 and rapid oxidation and reduction of its 

 metal oxides themselves in the burning gas 

 mixture. The power which catalyzers have 

 of existing in two or more states of oxida- 

 tion seems to apply also to the ceria of the 

 Welsbach mantle. Whatever the truth 



