CHEMICAL COMPOSITION OF KARROO ASH. 1 35 



Mr. Croghan found the following maxuna and minima per- 

 centages in the ash of the manures analysed by him: — 



Potash. Lime. Phosphorus 



Pentoxide. 



Per cent. Per cent. Per cent. 



Cape Province — 



Maxima 18.57 16.82 3.50 



Minima 3.56 4.53 1.32 



Orange Free State — 



Maxima 16.50 14.16 2.95 



Minima 3.74 3.66 1.20 



The wide variations between these maxima and minima 

 point to a considerable variation in the purity of the several 

 kraal manures examined. Some of them must have been con- 

 siderably mixed with sand. And the consequence of such ad- 

 mixtures is that the manures so contaminated yield ash of very 

 inferior quality, even when carefully burnt under all the advan- 

 tages of a chemical laboratory. When roughly burnt on the 

 farm, an additional variation is introduced, depending on the 

 degree of completeness to which combustion is carried ; and after 

 the manure has been burnt, and the ashes are collected, a further 

 contamination may arise by scraping earth together with the 

 ashes. 



So we see that Karroo ash is subject to three sources of 

 variation of composition: — 



1. The original kraal manure may be more or less mixed 

 with sand. 



2. The manure may be incompletely burnt, and may there- 

 fore contain much unburnt carbon or charred material. 



3. The ash, after burning, may have been mixed with earth. 



It may be that, either by force of circumstances beyond 

 control, or through carelessness, all three sources of contami- 

 nation may operate in one and the same case, and then we have 

 a very inferior Karroo ash indeed; and, on the other hand, the 

 greatest care may be exercised in each process, and combine to 

 produce an excellent ash. What the result of repeated incor- 

 porations of unburnt material and sand at each of the three steps 

 indicated above may be, we can imagine when we find that, in 

 spite of professional care exercised in the chemical laboratory 

 when burning the manure and collecting the ash, so much earth 

 had got incorporated with the original manure as to lower its 

 quality to that of the minima for the Cape Province jn the last 

 of the above tables, for, as a matter of fact, these three per- 

 centages belong to one sample, and represent the ash of what 

 was evidently a very impure kraal manure from the farm Sekre- 

 taris, in the Kimberley district. 



Here I take leave of Mr. Croghan's work for a while, in 

 order to turn to some investigations carried on at intervals during 



