June 15, 1906.] 



SCIENCE. 



907 



drated salts, it may be held by capillary 

 forces in the leaf, or it may be in all three 

 conditions. This question of the condition 

 of the moisture in tobacco will not be dis- 

 cussed in this paper. That tobacco may be 

 considered to have a 'vapor pressure' may 

 be safely assumed from every-day experi- 

 ence, for if it is kept in a dry atmosphere 

 it dries, and if in a moist atmosphere it 

 becomes moist. The object of this investi- 

 gation was to determine the magnitude of 

 this vapor pressure. When this had been 

 determined the next step was to find some 

 material which would automatically main- 

 tain that vapor pressure. 



Over two years ago the following experi- 

 ments were conducted by the author under 

 the direction of Professor Wilder D. Ban- 

 croft, of Cornell University. A plug cut 

 tobacco (Old Gold) was used and the ob- 

 ject of the first experiments was to find 

 under what conditions the weight of the 

 tobacco would remain the same as when 

 the box was first opened. As the vapor 

 pressure of sulphuric acid solutions had 

 been determined quite accurately and over 

 a great range of concentrations, solutions 

 of sulphuric acid were employed in the 

 tests. A number of solutions were pre- 

 pared having densities varying from 1.24 

 to 1.38, and a large quantity of each (about 

 300 c.c.) was used so as to avoid material 

 changes in composition. It was already 

 known that the vapor pressure of tobacco 

 probably lay between the vapor pressure of 

 the two end solutions. These solutions 

 were put into desiccators, such as are used 

 in chemical laboratories, and the tobacco 

 was placed on a watch glass which rested 

 on a wire tripod, which in turn rested upon 

 the shoulder of the desiccator. The weight 

 of each sample of tobacco had previously 

 been determined by weighing on the tared 

 watch glass. After standing for two weeks 

 in the closed desiccator the watch glass and 



the samples of tobacco were again weighed. 

 Approximately the same quantities of to- 

 bacco wex'e used in each desiccator, so that 

 the surface exposed should be nearly the 

 same throughout. 



The samples of tobacco, which stood over 

 solutions which tended to maintain in the 

 air a greater percentage of moisture than 

 the tobacco, would gain in weight, and on 

 the contrary the solutions having the less 

 vapor pressure than the tobacco would 

 cause the tobacco to lose in weight. Also, 

 the greater the difference between these 

 pressures the faster would the loss or gain 

 occur. The following are the results of 

 this set of experiments : 



Table I. 



Change in the weight of plug-cut tobacco standing 



over sulphuric acid solutions of different 



strengths. 



In the accompanying figure (1) the per 

 cent, loss or gain in weight has been plotted 



Fig. 1. Showing the loss or gain in weight in (Old 

 Gold) plug cut tobacco after two weeks. 



