232 



Journal of Agricultural Research 



Vol. XX, No. 3 



decided to be consistent with our previous conclusions as to the manner 

 in which formaldehyde solutions injure the treated seeds upon which 

 they dry. If injury occurred as the result of the close adherence to the 

 seed of concentrated formaldehyde gas formed by the decomposition of 

 paraformaldehyde deposited on the surface as the seed dried, then it 

 would follow that well-aerated seeds might very probably escape injury 

 by virtue of the rapid breaking down of the polymer and its escape by 

 diffusion into the air. Formaldehyde gas is heavier than air, so that if 

 seeds were dried in large quantities in sacks or in boxes, diffusion would 

 be slow and the air around the seeds would become saturated with gas, 

 which would be held around them long enough to cause seed injury. 



The evaporation of but a relatively small quantity of paraformaldehyde 

 in a closed space saturates the atmosphere so that further breaking down 



T/ME //V WEEKS 

 O I 2 3 4 S 6 7 8 9 fO // 12 i3 fit JS /6 17 tS 



8 



I 7 



K4 



Fig. 5. — Graph showing the diminution in the rate of evaporation of paraformaldehyde inclosed in a 



desiccator of 2,400-cc. volume. 



of the solid is inhibited by the partial pressure of the formaldehyde gas. 

 This was shown experimentally by placing some paraformaldehyde in 

 desiccators at the same time that dishes containing approximately the 

 same quantities were evaporating in the open air of the room. The rate 

 of evaporation of each sample was measured by the loss in weight after 

 successive weekly intervals. Figure 5 illustrates the initial rapid rate of 

 evaporation of a sample in the open air and the slowing up of that rate 

 when it was placed in a 2 ,400-cc. desiccator containing calcium chlorid as 

 a drying agent. When the sample was removed from the desiccator the 

 rate increased again, and the curve representing this period shows a 

 steady , even fall, until after 1 8 weeks the solid had practically disappeared. 

 If we compare the curve with figure 1, we note that whereas when the 

 sample is exposed to the open air it disappears entirely, when it is inclosed 

 and hence unaerated its evaporation practically stops. The exact weight 



