IOWA ACADEMY OF SCIENCE 
133 
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The substance was difficult to grind on account of adhering so* tena- 
ciously to the mortar. We therefore substituted a large agate mortar 
and pestle that seemed unusually hard and well polished, not having been 
used before. This rendered the grinding of each substance much more 
satisfactory. 
10. Calcium Sulphate, transparent selenite — 
The unground crystals 20.90 
After two hours’ grinding 17.66 
Removed hy grinding 3.24 
11. Sodium Thiosulphate — 
Unground crystals ...36.19 
After two hours’ grinding 24.43 
Removed hy grinding 11.76 
12. Barium Chloride — 
We decided to repeat the experiment (4) on account of the unexpected 
result. 
The unground crystals 14.76 
After two hours’ grinding * 14.85 
The grinding increases the amount of water 09 
A number of trials gave the same result. The crystals become moist 
and sticky by continual grinding. • 
13. Borax — ■ 
Unground crystals 41.62 
After two hours’ grinding 31;08 
Removed hy grinding 10.54 
14. Strontium Chloride — 
t 
Unground crystals 35.66 
After two hours’ grinding 23.22 
Removed hy grinding 12.44 
Thanks are due Miss Florence Klaus and I. B. Bleeker for all the 
determinations described in this paper. 
