CHEMICAL ANALYSES OF TOBACCO. 275 



hi the air-cured leaf. Details are riot at hand concerning the length of time the plants were, in each of these case*, 

 allowed to stand in the field after "topping", bnt the absence of nitric acid from the sample "cured in its juices 7 ' 

 and its presence in the " air-cured" sample would lead to the inference either that the former had been allowed to 

 remain longer in the field than the latter, or that the exceptionally prolonged and thorough fermentation had 

 resulted hit lie destruction of the nitric, acid originally present. The smaller proportion of ash would favor the first 

 assumption. 



In the case of the Perique tobacco "(Mired in its juices", therefore, we have manifestly an instance of the 

 conversion of a large proportion of both the citric and the malic acids into acetic (and butyric) acid, and the agreeable 

 fruity odor which this tobacco acquires during the fermentation, while partly due to these acids, would indicate the 

 presence of substances similar to the volatile oil obtained by Liebig during the fermentation of malic acid. It is 

 probable that this fermentation is similar iu character to that which takes place whenever the drying of the leaf is 

 retarded, and at the same time a moderate elevation of temperature is induced either spontaneously or through the 

 cautious application of artificial heat. It will be observed that the increase in the acetic acid in the foregoing 

 instance has not kept pace with the loss in citric and malic acids. This is no doubt partly due to the volatile 

 character of the former and to the periodical exposure to the air to which the product is subjected during the 

 curing. 



In the case of tobaccos like the foregoing, intended chiefly for chewing purposes, the object of the fermentative 

 part of the operation of curing is chiefly to produce or develop the flavor, and this is attained by the production 

 of volatile acids, and probably of the ethers of these acids as above described. In the case of smoking tobaccos, 

 the object to be attained is the improvement of the odor of the smoke and also the combustibility, on which 

 moreover the former closely depends. 



The fine aroma of good smoking tobacco is dependent on an exact regulation of the operation of combustion, 

 so that a certain quantity of einpyreuuiatio products may be formed and no more. It is hardly necessary to add 

 that the nature of these products, as well as the quantity produced, depends upon the degree of completeness of 

 the combustion. An absolutely complete combustion of tobacco produces only carbonic acid, water, and nitrogen, 

 all absolutely inodorous substances. A simple destructive distillation of tobacco, without combustion, furnishes a ' 

 mixture of liquid and gaseous products most offensive in odor even in the case of fine tobacco, and absolutely 

 dissimilar from the perfume of the same tobacco when smoked. The operation of smoking tobacco, therefore, 

 involves a nicely adjusted combination of destructive distillation and combustion. The more perfectly a tobacco 

 burns the less odor it involves iu burning; on the other hand, the slower and less perfectly it burns the stronger is 

 the odor, until the point is reached when the odor becomes simply offensive and the tobacco becomes unfit for 

 smoking. 



The changes produced in the operation of curing smoking tobacco, must therefore be effected primarily with a 

 view to modifying or, as uncured tobacco is always imperfectly combustible, to increasing the combustibility. 



CAUSES UPON WHICH THE COMBUSTIBILITY OF TOBACCO DEPENDS. 



Schloesing (Comptes-Rcndus, 1, 042 and 1027), to whom more than to any other investigator we are indebted for 

 our present knowledge regarding the chemistry of tobacco, first pointed out in the year 18GO the existence of a 

 connection between the "combustibility" of tobacco (i. e., the property it possesses of remaining incandescent, 

 glowing for some time after being ignited) and the percentage of potassium carbonate it yields on incineration. 

 The conclusions attained by this author are as follows : 



1. The soluble part of the ash of a combustible tobacco always contains potassium carbonate (tobacco contains, 

 according to Schloesing, no sodium); or, in general, a tobacco is the more combustible the more alkaline the ash. 



2. The soluble part of the ash of a difficultly combustible tobacco contains no potassium carbonate ; it ordinarily 

 contains lime, whence it follows that in combustible tobaccos the quantity of potash exceeds in equivalent proportion 

 that of the sulphuric acid and chlorine, and that in difficultly combustible tobaccos the reverse is the case. 



3. A difficultly combustible tobacco becomes combustible if the potassium salts of an organic acid (malic, 

 citric, tartaric, oxalic, etc.) be added thereto in such quantity that the potash in the ash exceeds in equivalent 

 porportions the sulphuric acid and chlorine. 



4. A combustible tobacco becomes difficultly combustible if a mineral salt (sulphate or chloride of calcium, 

 magnesium, ammonium, etc.) be added iu such quantity that the sulphuric acid and chlorine exceed in equivalent 

 proportions the potash in the ash. 



Schloesing finds that while the presence of nitrates promotes the combustibility to a certain extent, their value 

 is only secondary. Very combustible tobaccos have been found to be very poor in nitrates, while other, quite 

 difficultly combustible tobaccos, were rich iu nitrates. 



Schloesing gives the following explanation of the results of his observations on the foregoing subject: 



I have observed that the alkaline salts of malic, citric, oxalic, pectic, aud tartaric acids, when heated in close vessels, swell up 

 strongly, without donbt because they melt in decomposing, and leave a very voluminous coal that possesses little solidity and is very 

 porous: while the lime salts under the name circumstances do not alter in volume, and leave a very compact and coherent coal. Now, 



