AVAILABILITY OF POTASH IN GROUND ROCK. 13 



On account of tlic «;reat interest which has Immmi aroused in this 

 important subject and in order to pres(Mit all the facts in the most 

 accurate manner, the \vorlv of previous experimenters will be jriven 

 in as nuich detail as space will i>ermit. It is the intention to bring 

 tosfethei- all the information and evidence that the literature of the 

 subject ati'ords, whether it api)ears to be favorable to the use of 

 ground feldspar, or the reverse. 



In 1841) Salm-IIorstmar" pul)lishe(l in a German scientific journal 

 a method of prei)aring an artificial soil which, while being open, 

 porous, and of a soft texture, should be absolutely free from all 

 plant foods except those which were purposely added to it. The 

 purest crystallized sugar was burned to a light form of charcoal and 

 found to be absolutely free from any impurity capable of furnishing 

 nourishment to i)lants. All sorts of ditferent substances were then 

 added to this material in other pots, and plants grown in them. In 

 this way the experiments were kept under accurate observation and 

 miicli information was obtained of the actual foods, and their forms, 

 which are necessary to carry on the nourishment of plants. A short 

 time after this investigation, in l.s.")(). a chemist named Magnus'' re- 

 peated these experiments, and also made othei's. In addition to the 

 pots filled with sugar-charcoal, some of the pots were filled with 

 coarsely pulverized feldsi)ar. It was found that the plants growing 

 in the feldspar made a good growth, even if no other food contain- 

 ing potash was added. The finer the feldspar was ground the better 

 was the development of the plants. Magnus sununed up the results 

 of his investigations as follows : 



(1) 111 the abseuce of all uiiiieral plant foods, barley attained a height of 

 about 5 inches only before dying. 



(2) The addition of very small aiiionnts of mineral plant foods cuahleil the 

 plants to reach complete develoinneiit. 



(.S) If too mncli plant food was ])resent. the jdants were stunted or refused to 

 grow at all. 



(4) In pure feldsi)ar barley made complete development and matured grain. 



(."») The development of growth varied with the coarseness or fineness of the 

 feldspar. 



In 1861 Reichardt,^ a distinguished agricultural chemist, advanced 

 the opinion that granite, porphyry, and other rocks rich in orthoclase 

 feldspar quickly give up their potash to plants when the particles 



are very fine. 



About 1881 Hensel,'^ a German writer and chemist, advocated the 

 use of ground rock or so-called " stone meal," not only in order to sup- 

 ply the requisite potash, but also the phosphates and other mineral 



« Jour, fiir Prakt. Chem., 1849. 4C,, 193. 

 b Ibid., 1850, 50, G5. 

 «• Ackerbau Chemie (1801). 

 d A. J. Tafel, Bread from Stones, 1894. 

 104 



