INTRODrCTION, 11 



of the organic acids to their peculiar property of swelling up to 

 many times their original volume and thus yielding a porous mass of 

 finely divided carbon when decomposed by heat. 



Nessler " made a large number of experiments on the effects of 

 various salts on the glowing capacity of filter paper, his method 

 being simply to impregnate strips of the jjaper with solutions of the 

 salts of definite strength. His principal conclusions are (1) that 

 potash, especiall}' in the form of sulphate and carbonate, acts very 

 favorably on the fire-holding capacity, while lime and magnesia exert 

 no marked effect except to whiten the ash; (2) that chlorids are very 

 injurious, and (3) that potassium nitrate gives a (juick but incom- 

 plete combustion, while calcium and magnesium nitrates act very 

 favorably. Nessler admits that the organic potash salts favor the 

 fire-holding capacity, but combats the theory of Schhising in ex- 

 ])lanation of their favorable action. He points out that the ease with 

 Avhich these salts are deconii)osed by heat leads to carbonization, or 

 " coaling," of the tobacco in advance of the burning area, which is a 

 very undesirable property; and, moreover, that potassium sulphate, 

 entirely lacking the property of swelling and yielding a carbonace- 

 ous residue when heated, also exerts a markedly beneficial influence 

 on the fire-holding capacity. Nessler assumes that the favorable ac- 

 tion of potash salts is due to the formation of a small amount of 

 free potassium during the combustion, which serves as an energetic 

 oxygen carrier; or, in other words, it is simply a catalytic action. 



]Mayer '' has supplemented this work by including in his experi- 

 ments many organic compounds, and concludes in general that these 

 latter favor the burning with a flame, while they decrease the glowing- 

 capacity. The inorganic salts in general, especially those of potas- 

 sium, favor the glowing capacity. 



Nessler and Mayer based their conclusions on the supposition that 

 the compounds tested would exert the same influence on tobacco as on 

 filter paper, but this is by no means the case. The chief reason for 

 this appears to be in the relative sensibility of filter paper and tobacco 

 toward the salts affecting the- glowing capacity. Filter paper, which 

 is almost pure cellulose, is extremely sensitive toward metallic salts, 

 and when moistened with a solution of any of the potash salts con- 

 taining even as low as .25 per cent of potash will continue to glow 

 indefinitely, while, on the other hand, ten times this quantity may 

 entirely destroy this property. Tobacco contains, besides cellulose, 

 many other organic substances which are far less combustible, and 

 hence requires much larger quantities of these salts to produce appre- 

 ciable effects on the burning qualities. For example, small quanti- 

 ties of potassium chlorid greatly improve the glowing capacity of 



a Landw. Vers. Stat, 19, 309. » Landw. Vers. Stat., 38, 126. 



105 



