362 BULLETIN OF THE BUSSEY INSTITUTION. 
more ago, as a specific for clover points to the same conclusion as 
the foregoing results, inasmuch as there is good reason to believe 
that gypsum acts chiefly by setting free potash from certain sili- 
cates in the soil which had held it in rather firm combination. It 
has often been remarked that even superphosphate of lime may 
occasionally do a certain amount of good in the same way by vir- 
tue of the gypsum which is naturally contained admixed with it. 
There is nothing of novelty in the foregoing statements ; the facts 
set forth in them have long been familiarly known. Indeed the 
German chemist, Grouven,* long since expressed his belief that 
the so-called clover-sickness of land might be due to a lack of pot- 
ash; and this view has often been taught, subject of course to lim- 
itations and exceptions. Dr. Gilbert,t in his South Kensington 
Jectures, distinctly formulates the rule derived from the field-ex- 
periments of Mr. Lawes and himself, that potassie manures in- 
crease in a striking degree the growth of crops of the leguminous 
family (peas, beans, clover, etc.), as well as the amount of nitrogen 
they assimilate from a given area, although such manures give com- 
paratively little increase when applied to grain-crops. 
Mayer admits that chloride of potassium commonly produces a 
considerable increase of crop when applied to clover, but he urges: 
that in his own experiments he found it inferior to the sulphate. 
He found moreover in his experience that an application of a mix- 
ture of lime and chloride of potassium to clover just before sowing 
was highly disadvantageous. He argues that the chloride is by no 
means the best form in which to employ potash-compounds upon 
clover. In experiments on clover made on a loamy soil that was 
somewhat sour, and poor as to potash, lime, and magnesia, — and 
which was reputed to be tired of clover, — he got good crops by 
manuring either with sulphate of potash, or with lime, or with a mix- 
ture of the two; but, as was just now said, the crops obtained from 
chloride of potassium, or from mixtures of it and lime, were poor. 
He speaks of the superiority of the sulphate to the chloride as be- 
ing specially remarkable, and argues in favor of using the sulphate, 
even of low grades, instead of the chloride for this crop. 
E. — Neutral potash-salts, when applied by themselves, sometimes 
notably increase the yield of arable crops. 
It has often been remarked in Europe that the results obtained 
* “¢ Hoffmann’s Jahresbericht der Agrikultur-Chemie,” 1862, 5. 140. 
+ ‘‘American Journal of Science,” 1877 (3), 13. 30. 
