22 BURNING QUALITIES OF TOBACCO. 



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The fact that the calcium and magnesium salts produce a white ash 

 has already been mentioned, and at least one of these is essential to 

 this property. On the other hand, tobacco containing excessive 

 amounts of lime gives an ash which, although it is very light in color, 

 lacks cohesion, or. in the language of the trade, it " flakes.'' This is 

 a very objectionable property and must always be taken into account 

 in judging the burning qualities of tobacco. The potash salts, more 

 especially the organic compounds, yield an ash which is firm and 

 compact but dark in color. From these facts, then, it is clear that 

 potash and lime combined in the proper proportion are essential to a 

 firm, light-colored ash. There is no apparent reason to suppose that 

 magnesia is of any special significance in this connection further than 

 the fact that it acts like lime. 



THE RELATION OF THE ORGANIC CONSTITUENTS TO THE 

 BURNING QUALITIES. 



The organic compounds constitute the material which is consumed 

 in the combustion of the tobacco, and in some way the mineral con- 

 stituents, more particularly the potash salts, impart to this material 

 the proj^erty of burning without flame. If the mineral constituents 

 are extracted from a leaf of tobacco, it will then only burn with a 

 flame, the glowing capacity having been entirely lost. However, 

 some of the organic compounds show a greater tendency to burn with 

 a flame than do others, and hence act less favorably on the glowing 

 capacity, for, as has been stated, these two qualities usually stand in 

 inverse ratio to one another. The principal compounds or classes 

 of compounds which need to be considered in this connection are cel- 

 lulose, the organic acids, pectin, the so-called tobacco tars, plant 

 wax, the sugars, nicotine, and other organic nitrogenous compounds. 

 For the purpose of studying the composition of the leaf with refer- 

 ence to its burning qualities we may consider cellulose, which con- 

 stitutes from 10 to 15 per cent of the total weight, as the fundamental 

 or basic material, which receives its capacity for glowing from cer- 

 tain mineral salts. Pure cellulose in the form of filter paper is 

 exceedingly sensitive to the catalytic action of these mineral salts, 

 very small quantities of them being sufficient to cause the paper to 

 burn without flame indefinitely, but when the other organic constitu- 

 ents of tobacco are present this sensibility is greatly affected and 

 much larger quantities of the catalytic agent are necessary to pro- 

 duce a good fire-holding capacity. Cellulose, then, must be consid- 

 ered as a very favorable factor in promoting this property of hold- 

 ing fire. 



There are a large number of organic acids normally occurring in 

 tobacco, but of some of these practically nothing is known. Atten- 



105 



