GRIMSLEY. | Gypsum as a Fertilizer. 131 
periments to disprove this latter statement, and he found that 
meat mixed with gypsum and allowed to stand for a consider- 
able period of time showed not the slightest difference in time 
of putrefaction from meat not so treated. This theory is given 
in a brief summary by Stockhardt :” 
‘¢Gypsum acts chiefly through its sulphuric acid, which on the one side pro- 
cures soluble ammonia from the humous constituent of the soil and furnishes 
this to the plant at a period when it is especially inclined to the production of 
leaves and stems; and on the other side, strengthens and increases the power of 
plants to absorb ammonia from the atmosphere, and this in greater proportion as 
they are more abundantly endowed with delicate and juicy leaves and are thus 
already fitted by nature to make a more abundant use of the atmosphere.”’ 
The fact that gypsum absorbs moisture readily was thought 
by some to explain its value.’ In wet seasons it took up the 
moisture and held it, and in dry seasons furnished the moisture 
to the plants. Some even thought that plaster had the power 
to draw moisture from below during periods of drought. Gyp- 
sum is a good absorbent of moisture, but it retains the liquid 
very closely, and while it may be of some value in this way, 
other substances, as ordinary lime, would be better. 
DAVY’S THEORY. 
Sir Humphrey Davy and others before and after his time 
have regarded gypsum as a direct source of plant food. Davy 
found that clover contained about two hundred weight per acre 
of sulphate of lime, and that this was the amount of gypsum 
which produced the greatest benefit on the soil, so he argued 
the gypsum entered the plant as sulphate of lime. 
An examination of the table of plant composition given earlier 
in this chapter shows that lime and sulphuric acid are present 
in the plants benefited by gypsum. Other tables give sulphur 
as an element in plant ash rather than sulphuric acid. So sul- 
phur was supposed to come from the gypsum which did not 
enter directly as plant food, but was first broken up into its 
parts. This action was supposed to depend on the presence of 
humous acids, whereby the gypsum was broken up into humate 
of lime and sulphuric acid. If too little humus were present 
51, A Familiar Exposition of the Chemistry of Agriculture, p. 226, 1855. 
