Souls of the South-Western Districts of the Cape Colony. 133 
96 per cent., and then with absolute alcohol, and dried for two 
hours in a water oven. The weight of the crucible containing the 
potassic platinic chloride having been taken, the precipitate is 
washed through with boiling water and the crucible, after again 
washing with alcohol, is dried and weighed, and the difference 
between the two weighings taken as the amount of potassic platinic 
chloride. This amount, multiplied by -193 gives the quantity of 
potash (K,O) in the 10 grammes of soil taken. 
For the deternunation of phosphoric oxide 25 grammes of the “ fine 
earth”’ is placed in a marked 500 c.c. flask, 25 cc. of concentrated 
nitric acid are added, and the mixture is thoroughly shaken. Fifty 
¢.c. of concentrated sulphuric acid are next added and the mixture is 
again carefully shaken up. It is then gently heated, shaking at 
frequent intervals. If this does not lead to complete oxidation more 
nitric acid is added and the heating continued. Finally the mixture 
is cooled and diluted to the mark with distilled water: it is then 
well shaken and filtered. Two hundred. c.c. of the filtered solution 
{equivalent to 10 grammes of soil) are placed in an Erlenmeyer 
flask of suitable size, and very nearly neutralised with strong 
ammonia solution, a few drops of nitric acid being used to acidulate 
the mixture in case the limit is overstepped. Two hundred c.c. of 
molybdic solution—prepared by dissolving 150 grammes of ammonic 
molybdate in a litre of water, and adding this to a litre of nitric acid 
of specific gravity 1:°20—are added, and the mixture is heated to a 
temperature of 50° C. for three hours in a water oven, and allowed 
to cool completely. The liquid is decanted through a small filter 
and the precipitate in the flask washed with diluted molybdic 
solution. It is then dissolved with warm 5 per cent. ammonia, and 
the resulting solution is at once very faintly acidulated with-hydro- 
chloric acid. From a burette is then added 20 c.c. of magnesia 
mixture, drop by drop, at the rate of 1 c¢.c. every five seconds, 
and then 25 c.c. of 5 per cent. ammonia. The mixture is shaken 
for a short time and allowed to stand for twohours. The precipitate 
is filtered through a weighed Gooch crucible and washed with 6 per 
cent. ammonia solution. The crucible is dried at first on an iron 
plate and then ignited in a furnace for fifteen minutes. It is then 
cooled and weighed, and from the weight of the precipitate contained 
the amount of phosphoric oxide in the soil is calculated. 
I have detailed the methods employed in our investigations at 
some length, for two reasons: firstly, where vastly different results 
are arrived at by the employment of different methods, it is always 
desirable to be able to gauge the significance of the results from a 
knowledge of the method; and secondly, when investigations, such 
