Us IXSKCTUIDES, FUNGICIDES, AND WEED KILLERS. 



which is done commercially in cast-iroa vessels, hydrochloric acid is 

 given off and potassium sulphate formed. 



Properties. — Potassium chloride is very soluble in pure water. 

 320 grammes dissolve in 1 litre of \vater at 10° C, 570 grammes in 1 

 litre at 100 (". Potassium sulphate is less soluble, a litre of pure 

 water dissolves 8-4 grammes at 0° C. and 260 grammes at 100° C. 



Action on Plants. — Potash is a necessary plant food. In soils 

 where potash is quite absent plants languish and finally die before 

 maturing their seed. Such soils are rare. They are such as contain 

 a large proportion of limestone, peat, or sand. Potash may be given 

 to the plant as potassium chloride as well as the sulphate or nitrate. 

 The crude salt from the mines is generally used for the purpose. If 

 soil be dissolved by aid of sulphuric and hydrofluoric acids, and if the 

 potash which it contains be isolated, enormous amounts are found per 

 hectare. The German agronomists calculate this amount at 30-40 

 tons per hectare (12-16 tons per acre). Berthelot found 3o tons 

 at Meudon (14 tons per acre) and Deherain 32 tons at Grignon 

 (12-8 tons per acre). This potassic mass is not in a state of soluble 

 chemical combination, but it may be dissolved by the acid juices 

 of the roots which it appropriates in sufficient amount. When potassic 

 manures are added to soils of this nature, and they form the great 

 majority, no benefit accrues to the plant, and the spots where they are 

 applied cannot be recognized, no increased yield being obtained. 

 Potassium manures are only useful as a supplementary material when 

 the soil does not contain it in any form. Then its influence makes 

 itself felt especially when the crop is sustained by other chemical 

 manures such as sulphate of ammonia, nitrate of soda, and super- 

 phospate. Farmyard dung which contains 5 kilogrammes (11 lb.) of 

 potash per ton, suffices with the (potash) salts contained in the soil to 

 meet the requirements of agriculture. The belief of the great efficacy 

 of potash salts in all soils, established by Liebig, has not been con- 

 firmed in practice. An excess of potash salt may, on the contrary, be 

 injurious to certain plants. Heinrich was the first to observe the 

 injurious effects of certain salts, such as potassium chloride and 

 magnesium chloride, nitrate of soda and sulphate of ammonia on ad- 

 ventitious plants. Steglich has specially studied the action of potas- 

 sium chloride on farm crops with the following results : — 



TABLE XVIII. — Shelving the Action of a 30 jjer cent Solution and a 15 per cent 

 Solution of Potassium Chloride (Muriate of Potash) on<Farm Crops. 



