POTASS I CM, RUBIDIUM, CAESIUM, AND LITHIUM 539 



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

 cream of lartar, which is the acid tartrate of potassium, C 4 H. 5 KO 6 . T 

 This salt also separates as a sediment from wine. When the plants, 

 containing one or more of the salts of potassium, are burnt, then the 

 carbonaceous matter is oxidised, and in consequence the potassium is 

 obtained in the ash as carbonate, K 2 CO 3 , which is generally known 

 as i><>f<ixhes. Hence potashes occur ready prepared in the ash of 

 plants, rtnd therefore the ash of land plants is employed as a source 

 for the extraction of potassium compounds. Potassium carbonate is 

 extracted by lixiviating the ash with water. 8 Potassium carbonate 



7 As plants always contain mineral substances and cannot thrive in a sphere which 

 docs not contain them, especially which is free from the salts of the four basic oxides, 

 K a O, CaO, MgO, and Fe. 2 O 5 , and of the four acid oxides, CO 2 , N. 2 O 5 , PoO 5 , and SO 3 , the 

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

 With the present store of chemical data only one answer is possible to this question, 

 and it is still only a hypothesis. This answer was particularly clearly expressed by 

 Professor Gustavson of the Petroffsky Agricultural Academy. Starting from the fact 

 (Chap. XI. Note 55) that a small quantity of aluminium renders possible and 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 

 compounds lowers the temperature of reaction and in general facilitates chemical reac- 

 tions in plants, and thus aids the conversion of the most simple nourishing substances 

 into the complex component parts of the plant organism. The province of chemical 

 reactions proceeding in organic substances in the presence of a small quantity of mineral 

 substances lias as yet been but little investigated, although there are already several 

 disconnected data of this kind, and although a great deal is known concerning such reac- 

 tions among inorganic compounds. The essence of the matter may be expressed thus 

 two substances, A and B, do not react on each other of their own accord, but the addi- 

 tion of a small quantity of a third particularly active substance, C, produces the reac- 

 tion of A on B, because A combines with C, forms AC, and B reacts on this new com- 

 pound, which has a different store of chemical energy, forming the compound AB or its 

 products, and setting C free again. 



It may here be remarked that all the mineral substances necessary for plants (those 

 enumerated at the beginning of the note) are the highest saline compounds of their 

 elements, that they enter into the plants as salts, that the lower forms of oxidation of the 

 same elements (for instance, sulphites and phosphites) are harmful to plants (poisonous) y 

 and that strong solutions of the salts assimilated by plants (their osmotic pressure is 

 great and contracts the cells, as De Vries showed, see p. 822) not only do not enter into 

 the plants but kill them (poison them). 



Besides which, it will be understood from the preceding paragraph that the salts of 

 potassium may become exhausted from the soil by long cultivation, and that there may 

 therefore be cases when the direct fertilisation by salts of potassium may be profitable. 

 But manure and animal excrements, ashes, and, in general, nearly all refuse which may 

 serve for fertilising the soil, contain a considerable quantity of potassium salts, and 

 therefore, as regards the natural salts of potassium (Stassfurt), and especially potassium 

 sulphate, if they often improve the crops, it is in all probability because they influence 

 the properties of the soil. The agriculturist cannot therefore be advised to add 

 potassium salts, without making special experiments showing the advantage of such a 

 fertiliser on a given kind of soil and plant. 



8 The animal body also contains potassium compounds, which is natural, since animals 

 consume plants. For example, milk, and especially woman's milk, contains a somewhat 



