POTASSIUM, KUBIDItTM, CJ3SIUM, AND LITHIUM 647 



found to have retained a somewhat considerable percentage of the 

 potassium compounds. If a salt of potassium be taken, then during 

 the nitration an equivalent quantity of a salt of calcium which is also 

 found, as a rule, in soils is set free. Such a process of filtration* 

 through finely divided earthy substances proceeds in nature, and the 

 compounds of potassium are everywhere retained by the friable earth 

 in considerable quantity. This explains the presence of so small an 

 amount of potassium salts in the water of rivers, lakes, streams, and' 

 oceans, where the lime and soda have accumulated. The compounds of 

 potassium retained by the friable mass of the earth are absorbed as au 

 aqueous solution by the roots of plants. Plants, as everyone knows^ 

 "when burnt leave an ash, and this ash, besides various other substances, 

 without exception contains compounds of potassium. Many land 

 plants contain a very small amount of sodium compounds, 6 whilst 

 potassium and its compounds occur in all kinds of vegetable ash. 

 Among the generally cultivated plants, grass, potatoes, the turnip, 

 and buckwheat are particularly rich in potassium compounds. The 

 ash of plants, and especially of herbaceous plants, buckwheat strawj 

 sunflower and potato leaves are used in practice for the extraction of 

 potassium compounds. There is no doubt that potassium occurs in the 

 plants themselves, in the form of complex compounds, and often as salta 

 of organic acids. In certain cases such salts of potassium are even 

 extracted from the juice of plants. Thus, sorrel and oxalis, for example, 

 contain in their juices the acid oxalate of potassium, 8 HK0 4 , which is 

 employed for removing ink stains. Grape juice contains the so-called 

 cream of tartar, which is the acid tartrate of potassium, 4 H a KO 6 .* 



3 If herbaceous plants contain much sodium salta, it is evident that these salts mainly 

 come from the sodium compounds in the water absorbed by the plants. 



* As plants always contain mineral substances and cannot thrive in a medium which 

 floes not contain them, more especially in one which is free from the salts of the four 

 basic oxides, K 3 O, CaO, MgO, and Fe 2 O 5 , and of the four acid oxides, 00 2 , N 2 Os, 

 'PgQj, and SQs, and as the amount of ash-forming substances in plants is small, the 

 question inevitably arises as to what part these play in the development of plants. 

 With the existing chemical data only one answer is possible to this question, and it fc 

 etill only a hypothesis. This answer was particularly clearly expressed by Professor 

 Crustavson of the Petroffsky Agricultural Academy. Starting from the faat (Chapter 

 "XI., Note 65) that a small quantity of aluminium renders possible or facilitates the 

 reaction of bromine on hydrocarbons at the ordinary temperature, it is easy to arrive at 

 the conclusion, which is very probable and in accordance with many data respecting the 

 reactions of organic compounds, that the addition of mineral substances to organic com- 

 pounds lowers the temperature of reaction and in general facilitates chemical. reactions 

 In. plants, and thus aids the conversion of the most simple nourishing substances into thp 

 complex component parts of the plant organism. The province of chemical 'reaction^ 

 proceeding in organic substances in the presence of a small quantity of mineral substance^ 

 lias as yet been but little investigated, although there afe already several disconnected 

 data concerning reactions of this kind, and although a great deal is known with regarfl 

 to such reactions among inorganic oorapounds. The essence of the matter may be ex* 



