18 BURNING QUALITIES OF TOBACCO, 



MINERAL AND ORGANIC ACIDS. 



In describing the results of the tests with the various salts these 

 have been grouped under the heads of the three bases, potassium, 

 calcium, and magnesium, but it is also instructive to consider them 

 arranged according to the acids with which these bases are combined. 



Chlorids. — All of the chlorids injure the burn, but that of potas- 

 sium much less than the calcium and magnesium salts. 



Sulphates. — All of the sulphates injure the fire-holding capacity, 

 but to very different degrees. The potash salt is decidedly less harm- 

 ful than that of calcium, while the magnesium compound is remark- 

 ably injurious, being comparable with the chlorids in this respect. 



Nitrates. — The potash salt is very favorable to the burn, but the 

 calcium and magnesium compounds produce little effect except when 

 present in very large quantities. 



Phosphates. — Dipotassium phosphate is practically neutral in its 

 effect, while the calcium and magnesium salts are somewhat harmful. 



Salts of organic acids. — The potassium salts are very favorable to 

 the burn, the calcium salts are slightly beneficial, and the magnesium 

 salts are somewhat injurious. 



It would seem from these results that the effect on the fire-holding 

 capacity of any element entering into the composition of the ash de- 

 pends more on the nature of its combination than on the quantity 

 which is present. In the case of sulphuric acid, for example, a 

 considerable quantity combined with potash would not seriously 

 injure the glowing capacity, while even a small amount of it in com- 

 bination with magnesium would entirely destroy this property. 

 Again, the organic acids when combined with potash are very bene- 

 ficial, but in combination with magnesia their favorable influence 

 entirely disappears. 



It is evident that the one element on which the fire-holding capacity 

 is entirely dependent is potassium. But it is equally essential that 

 part of the potash be in combination with organic acids, for it is 

 to this form chiefly that its beneficial action is due. The nitrate of 

 potash when present in considerable amounts undoubtedly contrib- 

 utes also to this property. Schlosing, as has been said, attributed 

 the beneficial effects of the organic potassium salts to the peculiar 

 property which they possess of swelling up to many times the 

 original volume when decomposed by heat, thus leaving a very 

 porous, finely divided residue of carbon, which continues to glow until 

 combustion is complete. This explanation, however, is inadequate, 

 for there are other salts which promote the glowing capacity but do 

 not yield the carbonaceous residue when heated. 



It will be observed that all the potash salts which favor the prop- 

 erty of glowing, including the nitrate, yield in the combustion the 



105 



