STUDIES ON THE CUEING OP LEAF TOBACCO. 



37 



days before being dried in the oven. (This material served also for 

 the data presented in Table VII.) The stems were also removed from 

 the second lot of leaves (b) and one half of each leaf maintained in a 

 bell jar at an average temperature of 12° C. (54° F.) for 48 hours, 

 while the second half of each leaf was similarly treated, but at an 

 average temperature of 27° C. (80° F.). These leaf halves were then 

 quickly dried at 90° C. The results of these experiments are given in 

 Table IX. 



Table IX. — Effect of temperature in hastening rate of curing. 



Material. 



(a) 

 Leaf killed 

 with alco- 

 hol (1911) 

 or with 

 heat (1912). 



(&) 



Leaf par- 

 tially cured 

 at 10° to 

 12° C. 



Leaf par- 

 tially cured 

 at 24° to 

 27° C. 



1911 samples: 



Total dry weight of 6 leaves, including stems grams. 



Starch (leaf web) per cent. 



Protein nitrogen (leaf web) do. . . 



1912 samples: 



Total dry weight of 5 half leaves, without stems grams. 



Starch per cent. 



Protein nitrogen do . . . 



61.1 

 28.47 

 1.90 



18.7 



41.74 



1.17 



61.5 

 25.17 

 1.94 



18.3 

 37 

 1.03 



57.6 



21.33 



1.59 



17.4 

 26.46 

 .87 



From the above table it is seen that where the leaf was allowed to 

 cure for 24 hours there was a loss of about 3.3 per cent of the starch 

 content at the lower temperature and of 7.1 per cent at the higher 

 temperature, while for the leaf tissue cured for 48 hours the losses 

 were 4.7 per cent and 15.3 per cent, respectively. There was no 

 decrease in protein in the first case at the lower temperature, but a con- 

 siderable decrease at the higher temperature; and in the second case 

 there was only a small decrease at the lower temperature, but the 

 decrease at the higher temperature was very marked. It is evident 

 that the rate of curing is proportional to the temperature, which is in 

 accord with the well-known principle that normal respiration, as 

 measured by the rate of evolution of carbon dioxid, increases regu- 

 larly with rise in temperature; and it is interesting to note that in 

 tobacco curing the rate of increase in the speed of the reactions in- 

 volved tends to obey the law of Van't Hoff that the speed of ordinary 

 chemical reactions is approximately doubled for each increase of 10 

 degrees centigrade in temperature, provided, of course, that in this 

 case the optimum temperature for the enzyms involved in curing is 

 not much exceeded. 



EFFECT OF MOISTURE ON THE RATE OF CURING. 



It is well known that the rate of drying is of fundamental import- 

 ance in practical tobacco curing, and when the quantity of water in 

 the leaf has been reduced to certain limits the progress of the curing 



