38 



BULLETIN 79, U. S. DEPARTMENT OF AGRICULTURE. 



is practically stopped. On the other hand, if too much moisture 

 remains in the leaf toward the end of the curing, when the leaf cells 

 are dying, abnormal processes of decay, commonly known as pole- 

 sweat, set in, which result in the disintegration of the leaf tissue. 

 This latter trouble is due, however, to the invasion of foreign organ- 

 isms and needs no further consideration here. Aside from these ex- 

 treme conditions, we have to consider the effects of partial loss of 

 water by the leaf in the course of the curing process. It is stated by 

 some authorities that normal respiration is most active when the cells 

 are fully turgid; that is, in the presence of a maximum amount of 

 water. It appears from our experiments, however, that this prin- 

 ciple does not hold so far as it relates to tobacco curing. 



In 1911 two ripe tobacco leaves were selected and the midribs re- 

 moved. The two right-hand leaf halves were suspended in a tall 

 closed jar for 24 hours over concentrated sulphuric acid on which 

 was floated a dish containing a little caustic soda. The correspond- 

 ing left-hand leaf halves were similarly placed in a jar containing 

 only the caustic soda. The two lots of material were then killed 

 with hot alcohol in the usual manner and prepared for analysis. The 

 material which had stood over sulphuric acid was quite limp from loss 

 of water, but the other sample had scarcely wilted. The leaves used 

 in this experiment are comparable with those used for the 1911 

 experiment shown in Table IX and therefore originally contained ap- 

 proximately 28.5 per cent of starch and 1.9 per cent of protein nitro- 

 gen. A similar experiment was made in 1912 with a lot of five leaves, 

 the corresponding halves of which were subjected to the different 

 rates of drying for 28 hours and then quickly dried at 90° C. This 

 material is comparable with the 1912 samples used in the experi- 

 ment presented in Table IX and therefore originally contained ap- 

 proximately 42 per cent of starch and 1.2 per cent of protein nitrogen. 

 The results of the tests are shown in Table X. 



Table X. — Effect of partial drying on rate of curing. 



Material. 



Leaf par- 

 tially dried. 



8.7 

 12.61 

 1.49 



19.05 



30.76 



1.13 



Leaf not 

 dried. 



1911 samples: 



Total dry weight of 2 leaf halves 



Starch per cent. . 



Protein nitrogen do 



1912 samples: 



Total dry weight of 5 leaf halves grams. . 



Starch per cent. . 



Protein nitrogen do — 



8.7 



18.27 



1.56 



19.75 



34.55 



1.10 



The final dry weight of the two 1911 samples was the same, but as 

 there was a marked difference in starch content at the end of the 

 experiment it is evident that the leaf halves subjected to partial 

 drying were originally somewhat heavier than those not subjected to 



