PLANT PRODUCTS 



TABLE 4. WOOD ASHES. 



If in the Table 4 the figures represent pounds, it would take 4^ tons 

 of beechwood or 8J tons Scotch pine to be burnt for their production. 



in flues of blast-furnaces and boilers often contains a con- 

 centration of certain ingredients which may raise the potash 

 in the dust to 5 or 10 per cent. The vast majority of these 

 materials are, however, very disappointing, and rarely 

 repay transport, although by evaporation of an aqueous 

 extract a concentrate may be obtained. A useful waste 

 product is obtained in the case hardening of steel, during 

 which small parts of machinery are heated, then plunged 

 into mixtures some of which contain potassium ferro- 

 cyanide. Although this material when used for case 

 hardening lasts a long time, when worn out it is still rich 

 in potassium, and may even contain 20 per cent, potash. 

 The cyanides present would be prejudicial to plant life if 

 applied after the plant had started growth, and would also 

 tend to check germination. Similarly, even wood ashes, 

 being strongly alkaline, should be allowed some time to work 

 into the soil before the seeds are sown. 



The reactions of potassium sulphate with the soil are 

 very similar to those of ammonium sulphate. The potash 

 combines with clay and humus, and the sulphuric acid com- 

 bines with lime, and then washes out of the soil. Potassium 

 chloride reacts similarly, the chlorine taking lime and washing 

 out of the soil. When crude materials, like kainit, are applied 

 to the soil the sodium chloride washes out, leaving the potash 

 and most of the magnesia behind. These manures tend to 

 exhaust the soil of lime. Wood ashes, however, do not take 

 away lime out of the soil, but tend to make it alkaline and 



