84 TOBACCO LEAF. 



Other investigations in this country also do not sus- 

 tain the idea that the burning quality is entirely con- 

 trolled by the composition of the ash, and it is now be- 

 lieved that combustibility is the result of several condi- 

 tions, of which the ash is but one. These conditions 

 are, the abundance of organic potash salts (i. e., those 

 yielding carbonate of potash), the abundance but not ex- 

 cessive quantity of woody tissue, and the abundance of 

 sulphates. Mineral salts which fuse at the burning 

 temperature, such as the chlorides and phosphates of 

 potash and soda, hinder free burning ; and sugar, gum 

 and albuminous matters are difficult of combustion, and 

 therefore impede burning. 



Composition at Different Stages of Growth also 

 varies widely in both organic and mineral substances. 

 Original analyses of three Virginia tobaccos, set forth in 

 the Appendix, show that at time of cutting, the leaf con- 

 tains about twice as much ash as the stalk, and the 

 same quantity of nitrogen, more lime, and twice as much 

 insoluble matter ; but the stalk contains over twice as 

 much phosphoric acid as the leaf, one-third more potash 

 and four times the chlorine. The composition of the leaf 

 alone undergoes but little change from time of topping 

 until cured. The stalk, when cured, has gained slightly 

 in nitrogen and phosphoric acid, much in lime, but 

 has lost nearly one-fourth of its potash. 



How to Supply the Principal Ingredients is the vital 

 problem, in growing fine tobaccos. But a sharp distinc- 

 tion must be drawn between what the tobacco plant con- 

 tains, and how large a supply of the elements of the 

 plant food are essential for a successful crop. Chemical 

 analyses are valuable in determining absolutely the per- 

 centage of the food elements contained in the plant, and 

 they give an excellent basis for intelligently framing a 

 manurial supply, but afford little indication of the 

 quantity required. Under the old English system of 



