INCANDESCENT MANTLES. 



391 



that other metals having the same characteristics would act as exciters 

 when used in the proper proportions, and both attributed the high 

 incandescence of the mantle to changes in the state of oxidation 

 increasing the intensity of combustion on the mantle surface, while 

 Dr. Killing also pointed out that a catalytic action probably took 

 place. 



Dr. Bunte has given by far the best exposition of the theory of the 

 incandescent mantle, which if it does not make all points clear, yet 

 offers a simple and probable explanation of the observed phenomena, 

 which he ascribes to intense local temperature due to the ceria exer- 

 cising a power of attracting oxygen and causing its combination with 

 the flame gases. 



The remarkable influence which ceria exerts in awakening light 

 emissivity in the mantle becomes still more remarkal)le when one con- 

 siders that although the percentage by weight of the ceria is only 1, 

 yet that by volume it is enormously less. When nitrate of cerium is 



9 10 



Fig. 1.— Effect of ceria upon light emission of a thoria-ceria mantle. 



2 » 4 S 6 7 



Percentage of ceria. 



converted into ceria by the action of heat, but little change of volume 

 takes place, but when nitrate of thorium is decomposed in the same 

 way its conversion into oxide is accompanied by an increase in bulk of 

 an extraordinary character, the substance swelling up and producing 

 a light powder occupying many times the bulk of original salt, so that 

 in the finished mantle small indeed must be the space occupied by the 

 exciting ceria. 



This seems to point to some specific action on the part of the ceria, 

 and cases are not uncommon in which dilution with some inert material 

 increases physico-chemical action of the kind one would expect of the 

 ceria. If port or claret be shaken up with powdered charcoal, which 

 consists of nearly pure carbon, and the mixture is then filtered, the 

 color is but little changed, while if animal charcoal or some of the 

 artificially prepared imitations of it containing less than 10 percent of 

 carlwn distributed over the surface of inert mineral matter be used for 

 the same purpose, the liquid is absolutely decolorized. 



