STUDIES ON THE CURING OF LEAF TOBACCO. 11 



cold, and, after washing with hot water acidified with acetic acid, the 

 nitrogen in the residue is determined by the Kjeldahl method. Com- 

 parative tests of cured and uncured samples of tobacco show that the 

 Stutzer method regularly gives results about 0.2 per cent higher than 

 the Mohr method. The protein is estimated by multiplying the 

 nitrogen obtained as indicated by the usual factor, 6.25. 



Nicotine. — This constituent was determined by the method described 

 in Part VII of Bureau of Plant Industry Bulletin No. 102, entitled 

 " A New Method for the Determination of Nicotine in Tobacco," tests 

 having shown that this process gives as accurate comparative results 

 as does the well-known Kissling method. 



Nitric acid. — The method of Kissling * was followed in this deter- 

 mination. 



Ammonia. — This constituent was determined in the filtrate from 

 the protein nitrogen by the Folin method as modified by Pennington 

 and Greenlee. 2 Under the conditions, only traces of nicotine are car- 

 ried over into the receiver by the air current. However, in our 

 determinations the results were corrected by running check solutions 

 containing the same quantities of nicotine as were known to be con- 

 tained in the solutions from the tobacco samples. The temperature, 

 rate of air current, etc., were kept as uniform as possible in making 

 the determinations. 



Amid and amido nitrogen. — This value was obtained by taking the 

 difference between the total nitrogen and the sum of the protein, 

 nicotine, nitrate, and ammonia nitrogen. The figure obtained was 

 multiplied by 4.8 (the approximate factor for asparagin) for amid and 

 amido compounds. 



Total nitrogen. — The official Gunning method, as modified for 

 nitrates, was used. 



RESULTS OBTAINED IN THE FOUR-YEAR EXPERIMENT. 



In section A of Table III (p. 12) will be found the results of the 

 analyses of the leaf samples previously described. The leaf web and 

 the stems or midribs were, of course, analyzed separately, and the 

 results for the whole leaf were calculated from the ratio of leaf web 

 to stem in each case. As a matter of convenience, the ripe, uncured 

 leaf is designated in the table as "green." 



The content of pure ash of the cured leaves is higher than that of 

 the uncured leaves in proportion to the loss in dry weight in curing, 

 since there can be no change in the quantity of ash during the curing. 

 While the green leaves contain considerable but quite variable quanti- 

 ties of starch, the cured leaves contain practically none, as shown by 



* Kissling, Richard. Handbuch der Tabakkunde, des Tabakbaues und der Tabakfabrikation. Aufl. 

 2, Berlin, 1905, p. 78. 



* Pennington, M. E., and Greenlee, A. D. An application of the Folin method to the determination of 

 the ammoniacal nitrogen in meat. Journal, American Chemical Society, v. 32, p. 561-568, 1 fig., 1910. 



