36 BULLETIN" 79, IT. S. DEPARTMENT OF AGRICULTURE. 



Table VIII. — Diastatic activity ofuncured and partially cured tobacco leaves. 



Material. 



Total 

 weight of 

 material. 



Weight per 

 square foot. 



Loss of 



weight in 



curing. 



Weight of 

 leaf used. 



Relative 

 diastatic 

 activity. 



Experiment 1 (14 square inches of leaf sur- 

 face used): 

 A bottom leaf- 

 Green half 



Grams. 

 6.47 

 5.67 



7.634 

 4.836 



8.536 

 5.004 



Grams. 

 5.124 

 4.489 



7.354 

 4.659 



7.940 

 4.655 



Per cent. 



Grams. 

 0.5000 

 .4378 



.5000 

 .3167 



.5398 

 .3164 



4.41 



Cured half 



12.4 



5.48 



Experiment 2 (9.8 square inches of leaf sur- 

 face used): 

 2 top leaves— 



2.04 





36.7 



7.02 



A bottom leaf- 

 Green half 



2.48 



Cured half 



41.4 



6.50 







The above results show very clearly that there is a marked increase 

 in the diastatic activity of tobacco leaves during the curing process. 

 It seems probable that there is a similar increase in the proteolytic en- 

 zyms during the curing, but no attempt was made to determine this 

 point. 



TOBACCO CURING AS AFFECTED BY EXTERNAL CONDITIONS. 



Since respiration plays a fundamental r6le in tobacco curing, it is to 

 be expected that the external conditions, notably the temperature, 

 will have a decided influence on the curing process. The factors of 

 importance in this connection are the temperature and relative con- 

 tent of moisture, oxygen, and carbon dioxid of the surrounding 

 atmosphere and the presence or absence of light. We have made 

 some experiments on the relation of the first two of these factors to 

 the rate of curing, using the quantities of starch and protein hydro- 

 lyzed as a measure of the progress of the curing. 



EFFECT OF TEMPERATURE ON RATE OF CURING. 



In 1911 three lots of six leaves each were collected, using the pre- 

 cautions already described in detail, to have the three lots strictly 

 comparable. The stems were removed from the first lot of leaves (a) 

 and the leaf web killed by plunging into boiling absolute alcohol, 

 after which the leaf web and stems were dried at 80° C. The second 

 lot of leaves (b) was placed in a bell jar and maintained at a temper- 

 ature of approximately 10° C. (50° F.) for 24 hours, after which they 

 were treated exactly like the first lot. The third lot (c) was similarly 

 maintained at a temperature of approximately 24° C. (75° F.) for 24 

 hours and then treated like the other two lots. In 1912 the experi- 

 ment was repeated with two lots of five leaves each. The stems were 

 removed from the first lot (a), one half of each leaf being quickly 

 dried at 90° C, while the remaining leaf halves were chloroformed 

 and placed under favorable conditions for curing for a period of four 



