WOOD ASHES AS MANURE. 6j 



ashes have been applied, the rain, irrigation water, and air do not 

 penetrate so well, and in consequence the crop does not do so 

 well as on the untreated portions. This trouble is to be looked 

 for especially in soils containing much clay or fine silt. Many 

 of the black-looking soils from the Thabanchu and Ladybrand 

 districts are of this nature. If this is not the cause, then one 

 of the other causes mentioned above may be operating. The 

 remedy in all cases is to destroy the carbonates of potash and 

 soda by transforming them into sulphates. This is done by 

 applying gypsum and water. In the presence of water and air, 

 gypsum and carbonate of soda yield carbonate of lime and sul- 

 phate of soda (CaS0 4 + Na 2 CO s = CaCO s + Na a SOj. 



In the same way gypsum plus carbonate of potash gives 

 carbonate of lime plus sulphate of potash. 



The gypsum should be ground to a fine powder and applied 

 at about the same rate as the ashes were. It is necessary to 

 incorporate it with the soil and to keep the soil loose. Rain or 

 irrigation will do the rest. I very much doubt if gypsum can be 

 obtained at a reasonable price. Under the circumstances it will 

 perhaps be best to apply superphosphate, which contains a large 

 percentage of gypsum. This will also add phosphoric acid to the 

 soil, from which the crop will derive extra benefit. 



It is, however, better to prevent than to cure. I would 

 therefore recommend any one who would use ashes for manurial 

 purposes to mix them with an equal weight of gypsum or of 

 superphosphate, and to apply the mixture well in advance of 

 planting the crop. This applies equally well to potatoes. 



The treatment converts the carbonates of soda and potash 

 into sulphates of soda and potash, which latter compound is the 

 best form of potash to apply to crops in which " quality " is an 

 essential, and the only form of potash which can be used in safety 

 in a dry country. 



Composition of the Earths Upper Atmo- 

 sphere. — On pages 210 and 211 of the previous volume 

 allusion was made to the hypothesis that the outer layers of the 

 earth's atmosphere consist almost entirely of hydrogen. _ A. 

 Wegener* estimates that the hydrogen layer begins at a height 

 of 70 to 80 kilometres above the earth. The spectrum of the 

 aurora shows that as the height increases the intensity of the. 

 nitrogen lines diminishes, and that of the hydrogen lines is 

 increased. At a height of 200 kilometres, he thinks, the atmos- 

 phere consists of equal parts of hydrogen and coronium, the 

 latter predominating at greater heights. 



*Zeitschrift anorgan. Chemic, 1912, vol. 75, pp. 107-131. 



