24 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



washed and ignited asbestos, in order to allow freer circulation of air. 

 This precaution was not necessary for the success of the experiment, al- 

 though it had been found to increase somewhat the sharpness in the 

 change in the rate of dehydration. The crucible was now placed in a 

 small desiccator containing phosphoric oxide, and the whole was placed in 

 a thermostat maintained at 30°. From time to time the crucible was 

 rapidly weighed, the phosphoric anhydride being stirred in order to ex- 

 pose a new surface to the moist air. The results of this experiment are 

 recorded below. 



Rate of Dehydration of Baric Chloride. 



After several days more, the salt had lost very nearly all of its crystal 

 water, although the last portions, which must have been in tlie centre of 

 the various masses constituting the powder, naturally left more and more 

 slowly. Exposed to the somewhat moist air of the laboratory, the salt 

 regained in a few days all the water which it had lost. 



The only remarkable thing about this rather commonplace experiment 

 was the suddenness of the change in the rate after the first molecule of 

 water of ci-ystallization (0.0900 grams) had gone. Graphic representa- 

 tion will make the point clearer. In the accompanying diagram, the loss 

 of water (in grams) is plotted vertically, while time (in hours) is plotted 

 horizontally. 



