92 Dr. Karl Heumann's Contributions to 



2. The particles of carbon separated in the lower uncooled 

 parts of the flame rose upwards, and were deposited upon the 

 porcelain rod. 



The decrease in luminosity, unaccompanied by deposition 

 of carbon, which was noticed when the -rod was much de- 

 pressed in the flame, is to be traced to the fact that the tem- 

 perature necessary for separation of carbon could not be 

 attained in this part of the flame, which previous to the expe- 

 riment was already cooler than the upper part. 



These considerations teach us that, in order to obtain a large 

 deposit of carbon (as in the manufacture of lampblack &c), 

 the cooling of the flame should not be carried too far, while 

 at the same time the maintenance of a very high temperature 

 or the presence of much air should be avoided. Further, we 

 learn that, in order to obtain deposition of carbon, it is not ne- 

 cessary to cool the flame, inasmuch as the maintenance of a 

 high temperature is a necessary condition of the separation of 

 carbon. The object brought into the flame may be compared 

 to a redoubt which intercepts the balls shot forth. The cool- 

 ing action exercised is productive of carbon-deposition only 

 so far as it prevents the oxidation both of the particles of 

 carbon suspended in the flame and of those caught by the ex- 

 tended surface. 



Hence it follows that the surface of a glowing body immersed 

 in the luminous flame must become covered with soot. 



The carbon which is separated in a smokeless luminous 

 flame is burned partly in the outer, partly in the inner por- 

 tions of the flame : it is evident, however, that this burn- 

 ing will take place to a less extent where the flame is en- 

 closed by the solid body placed within it than where it is 

 surrounded by air. Even in the former part of the flame, 

 however, the supply of air is not altogether shut off ; hence 

 a part of the soot which has been deposited, and which is at 

 a high temperature, will be burned. Deposition of soot 

 is therefore generally somewhat less upon a hot than upon a 

 cooler surface ; nevertheless it may happen that a very cold 

 substance is scarcely, if at all, covered with soot. 



In performing the following experiment, which exhibits the 

 fact that a hot surface may have carbon deposited upon it, 

 care must be taken not to bring the surface covered with car- 

 bon into the air until it cools ; else the soot will almost imme- 

 diately be burned. A platinum basin is placed in a vertical 

 position ; the concave side is heated by means of a Bunsen's 

 lamp placed horizontally ; and a luminous flame burning at 

 the orifice of a tube is caused to play against the convex side 

 of the basin. A deposit of soot is soon noticed. By moving 



