INTRODUCTION. 9 



others which favor the complete combustion predominate, the ash 

 will be white, or very nearly so. 



From what has been said it is perhaps not surprising that the rela- 

 tion of the chemical composition to the burning qualities of tobacco 

 early attracted the attention of agricultural chemists, and this prob- 

 lem has led to a large number of purely chemical investigations, as 

 Avell as practical field experiments. But although more than fifty 

 years have elapsed since the publication of the first important paper 

 on the subject, by Schlosing, no one has as yet been able to offer a 

 satisfactory explanation of the conduct of different kinds of tobacco 

 as regards their burning qualities. Many theories have been put for- 

 ward from time to time, but they have all proved to be either funda- 

 mentally erroneous or inadequate to explain all the facts. Except a 

 few general relations which have been pretty fully established, the 

 results obtained by different investigators have led to widely different 

 and oftentimes contradictory conclusions. It will not be necessary to 

 discuss or even mention here all the work which has been published 

 on this important subject, and only those facts which seem to be best 

 supported will be briefly reviewed. 



In comparing the composition of the tobacco plant with that of 

 other agricultural crops, the most striking characteristic is its re- 

 markably high content of mineral matter, commonly spoken of as 

 the ash. In some cases the ash content reaches 25 per cent of the 

 total weight of the dry tobacco leaf, and the average is well above 15 

 per cent. For this reason by far the greater portion of the work of 

 chemists on tobacco has been devoted to the study of the composition 

 of this ash. 



Broadly speaking, there are two methods of attacking the problem 

 of the relation of the composition to the burn, one of which may be 

 called the analytical and the other the synthetical. Nearly all of the 

 investigations on this subject fall under the head of the analytical 

 method, which consists simply in making comparative analyses of 

 samples of tobacco having good and poor burning qualities, and at- 

 tempting to trace the relation between the differences in composition 

 and the good and bad burning qualities. An examination of the 

 composition of a typical tobacco ash will show how extremely diffi- 

 cult it is to draw any positive conclusions from any set of analyses 

 which will not be subsequently contradicted by other analyses. 



In the first place, there are present in tobacco three inorganic acids 

 and three bases, all of which occur in sufficient quantities to exert an 

 important influence on the burn and all of which are subject to wide 

 variations in quantity in different tobaccos. With such complex 

 variations it is almost impossible to single out those differences which 

 really exert determinative influences on the burn. But more impor- 



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