Soils of the South-Western Districts of the Cape Colony. 131 
too costly to be applied to samples which represent nothing but 
themselves.’’* As our analyses are intended to a certain extent to 
ascertain the agricultural value of the soils over wide areas it 
becomes necessary to include as far as possible only virgin soils that 
have not been subjected to modifying influences. The practice has 
been to take the sample sufficiently below the surface to keep it 
clear of the top growth and accumulations, and then to extend 
downwards to a depth not exceeding 12 inches. After having 
been spread out in the laboratory for some days the soil is digested 
with water and washed through a 4-millimetre sieve by the aid of 
a small brush, that which passes through being dried and the 
residue from the wash water after evaporation added to it. The 
combined weight of the two is then calculated in percentage of the 
original soil taken, and entered as ‘fine earth.’”’ This fine earth is 
utilised for the determination of lime, potash, and phosphoric oxide 
in the soil. The residue which does not pass through the $-milli- 
metre meshes is, after drying, sifted through a sieve with meshes 
1. millimetre in diameter; what passes through is known as 
“‘ coarse sand,’ and this is included together with the fine earth in 
determining moisture, organic matter, chlorine, and nitrogen. Re- 
garding these latter determinations I do not propose to say much on 
this occasion, rather confining my remarks to the inorganic plant-food 
constituents of the soil, namely lime, potash, and phosphoric oxide. 
The first step in the actual analytical process is the treatment of 
the sow with acid. Two hundred grammes of the fine earth are 
placed in a large flask and treated with 400 c.c. of hydrochloric acid 
of specific gravity 1115; allowed to remain for five days ‘at the 
ordinary temperature, shaking thoroughly from time to time. After 
the prescribed period of digestion has expired, the extract is filtered 
through a dry pleated filter into a dry flask. Two hundred and fifty 
c.c. of the filtrate are evaporated to dryness in a shallow porcelain 
dish at first over a small open flame, then on the water bath, and 
finally on a sand bath or in an air oven at 120° Centigrade until 
perfectly dry. During evaporation a few cubic centimetres of strong 
nitric acid are added to the extract. The dry residue is moistened 
with strong nitric acid and again evaporated to dryness: to expel 
the nitric acid the residue is moistened with hydrochloric acid and 
evaporated on the water bath to as near dryness as possible, taking 
care to stir towards the end so as to prevent the formation of crusts. 
This final residue, after warming in the air bath for an hour, is 
treated with warm water and a 20 per cent. solution of hydrochloric 
acid, and is then washed over into a 250 c.c. flask, boiled for fifteen 
* Wiley: Op. cit. p. 65. 
