the Theory of Luminous Flames. 377 



presence of those metallic salts which appear in the solid form 

 when the doors are opened. This conclusion tacitly assumes 

 the presence of solid matter in the flame of the blast-furnace. 

 Hirn does not appear to have examined the spectrum of this 

 flame ; and, so far as our knowledge extends, the contrary 

 assumption to that made by Hirn appears quite as credible 

 as his. 



Hirn thus assumes that the light from a flame which con- 

 tains solid matter must show evidence of polarization, and 

 that the absence of polarized light is only to be accounted for 

 by supposing that the solid particles become optically altered 

 at a very high temperature, and lose their power of reflecting 

 light. It appears to me that the facts observed by Hirn 

 would be much better explained by regarding the absence of 

 polarization as proof of the absence of solid particles in the 

 flame. This explanation would apply to the phosphorus- 

 flame, and perhaps also to the flame from the blast-furnace. 

 I have, however, convinced myself by experiment that the 

 non-recognition of polarized rays in the light coming from a 

 flame is not proof of the absence of solid matter in that 

 flame. 



The amorphous carbon present in the luminous flames of 

 ordinary combustible hydrocarbons reflects almost no light ; 

 these flames show no traces of polarized light when examined 

 by means of the polariscope. The light from many other 

 non-homogeneous bodies is also devoid of noticeable polarized 

 rays. We cannot, therefore, assume that the light emitted by 

 a flame containing a small quantity of finely divided solid 

 matter must show such a number of polarized rays as shall be 

 recognizable by the polariscope. Hydrogen-flames, rendered 

 luminous by the presence of platinum chloride, osmic acid, 

 ammonium chromate, ferric and cupric chlorides, &c, showed 

 no traces of polarized light when examined by means of 

 Arago's and Savart's polariscopes ; yet these flames certainly 

 contained solid matter. 



The flame of hydrogen containing chromyl dichloride also 

 failed to show polarized light : the smoke of this flame, and 

 also of the turpentine-flame, when examined in sunlight, 

 afforded evidence of polarization. I am inclined to trace the 

 polarizing action of the smoke in these cases to the presence 

 of condensed water, tarry matter, hydrochloric acid, &c, 

 which substances would be present as gases in the flame itself. 



I cannot, therefore, regard the non-detection of polarized 

 light as proof of the absence of solid matter in flame ; much 

 less can I agree with Hirn's statement, that " the solid par- 

 ticles lose their power of reflecting light at a white heat." 



