STUDIES ON THE CUEING OF LEAF TOBACCO. 29 



In the above scheme the changes which take place quantitatively 

 are indicated by solid lines, and partial transformations are indicated 

 by broken lines. The transformation of the sugars into nonvolatile 

 organic acids is bracketed, for the reason that, although the sugars 

 are quantitatively removed, it is not known to what extent the acids 

 are formed as intermediate products of oxidation. There is some 

 question as to whether citric acid is further oxidized during the curing 

 process, and it has not been actually proved that nitrogen-free acids 

 are formed by the hydrolysis of the amido derivatives of protein, 

 although this seems highly probable. The scheme merely presents 

 the course of events in the breaking up of the surplus food supply 

 in support of respiration, and does not take into account the move- 

 ments of the soluble products due to physiological translocation. 



It will be seen that the so-called ether extract, which is usually 

 included in the analysis of agricultural products and which is intended 

 to show the content of fat or oil, has not been considered in connec- 

 tion with our studies on the changes in composition taking place 

 during the curing. It has not been considered that this determina- 

 tion would throw any light on the problems in hand, for the extract 

 obtained from tobacco leaves is a hopelessly complex mixture, con- 

 taining a portion of the nicotine, chlorophyll, and its decomposition 

 products, tobacco resins, etc., and in reality containing at most very 

 small quantities of constituents which could be properly called fat 

 or oil. No methods are at present available for the quantitative sep- 

 aration of the several constituents of the ether extract, and it is 

 obvious that the crude extract would contain several constituents 

 already accounted for in the analyses. 



The results which have been presented and discussed in the pre- 

 ceding paragraphs apply more particularly to typical air curing. 

 Samples A and B of 1911, in Tables IV and V, should bring out any 

 differences in the final result of the curing when air curing is modified 

 by the moderate use of artificial heat. As a matter of fact these 

 duplicate samples, after curing, show almost exactly the same com- 

 position; so that, although the moderate application of heat hastens 

 the rate of curing, as shown by the appearance of the tobacco during 

 the progress of the process, the final result, so far as shown by the 

 analyses, is the same, whether or not the heat be applied. In the 

 case of flue curing, where much higher temperatures are used, no 

 comprehensive investigations have been made; but analyses of the 

 cured leaves which have been reported show that the curing changes 

 are of the same character as in air curing, the only difference being 

 that in flue curing the transformations are less complete. In typical 

 fire curing, in which the tobacco is only partially cured by the use of 

 heat, the relative completeness of the chemical changes involved 

 probably falls between that in air curing and that in flue curing. 



