130 University Geological Survey of Kansas. 
looked upon gypsum as a stimulant to the leaves of plants. 
This theory, which became prevalent, stated® that ‘‘ sulphate of 
lime acts as an irritant in favoring respiration and exhalation 
of plants.’’ 
Chaptal modified somewhat this theory and regarded the 
stimulation as due to the saline character given to the sap by 
the presence of gypsum, and as this mineral dissolved very 
slowly, it would gently stimulate and not irritate. : 
Gypsum rock is very porous and a good absorbent, so this 
property was long ago taken to explain its agricultural value. 
It was discovered that the atmosphere contained carbonate of 
ammonia which was carried down to the earth in rain water, 
and there it was thought to be held or fixed by gypsum. A 
good statement of this theory is given in Browne’s American 
Muck Book,” written in 1851. The carbonate of ammonia 
acted on the sulphate of lime so as to form sulphate of ammonia 
and carbonate of lime. This prevented the escape of the vola- 
tile carbonate of ammonia back into the air. A computation 
was made which showed that 100 pounds of common unburned 
gypsum would fix or form twenty pounds of ammonia contain- 
ing sixteen and one-half pounds of nitrogen. This would 
furnish a very large amount of valuable food to plants for their 
use; but now it is known that the amount of ammonia in the 
air is so small that it is very doubtful whether the amount so | 
fixed by gypsum is even appreciable to the plants. 
This theory was held and much elaborated by the chemist 
Liebig, who calculated that theoretically if forty pounds of gyp- 
sum were placed on a field, and only one-tenth of it entered 
plants as ammonia sulphate, there would be nitrogen enough 
for 100 pounds of hay, fifty pounds of wheat, or sixty pounds of 
clover. 
STOCKHARDT’S THEORY. 
Some have held that the gypsum fixed the ammonia formed 
within the soil by decaying vegetable matter; and further, that 
the gypsum hastened this decay. Davy tried a number of ex- 
49, Annales de Chimie 55, p. 312. 
50. Pages 68 to 75. 
