128 
W. B. Crump. 
samples weigh from 15 to 60 grams, and the weight is determined 
within a centigram. They are then placed in a quiet room or airy 
cupboard and left to dry at about 15"C. until the weight is constant. 
This takes from one to three months. The loss of weight is the 
required water-content. The dishes are then heated in a water- 
oven (at 100 ft C.) until the weight is again practically constant. This 
further loss at 100 f 'C. though recorded is ignored *because it can be 
of no service to the plant. It includes hygroscopic moisture and 
water of combination and its value is tolerably uniform for the 
same type of soil so that it affords a check on the determination of 
the water lost at 15°C. 
The dish and its contents are next subjected to a full red heat 
until all char has disappeared, and again weighed as soon as cold, 
or preferably placed in a desiccator to cool. The loss of weight is 
recorded as humus, as a more definite term than “ loss on 
combustion ” and quite in accordance with the use of the word 
humus to include all the decaying organic matter in the soil. The 
residue may consist entirely of vegetable ash, or may be almost 
wholly mineral in origin. If the soil is calcareous the lime must be 
reconverted into carbonate after combustion. 
Such is the process of analysis. The percentage composition 
of the wet soil is then calculated from the results. But partly to 
conform to agricultural practice and partly because the wet soil 
represents no fixed standard, the values are then manipulated to 
express them in terms of 100 parts of air-dry soil, i.e., of soil dried at 
15°C. The water-content, otherwise the loss at 15°C., then becomes 
an addition to the 100 parts. Clearly, if a wet peat loses just 50% of 
its weight on drying in the air, the air-dry peat was “ combined 
with ” 100% of water. The principle is sound though it has dis¬ 
advantages, for when the water-content is high originally it becomes 
much exaggerated in the final result. Even if agricultural analyses 
took note of the water lost on drying at 15°C. this disadvantage 
would not be apparent. But in the case of peats the statement of 
the water-content is paradoxical unless the exact expression receives 
careful attention, e.g., “ the water lost at 15"C. is 135% of the air-dry 
peat,” means that there are 135 parts of water lost on every 100 
parts of the air-dry peat that remains after drying. Slight 
differences are of course magnified in the same way, so that a 
variation of 1% in the water-content of a wet peat may become 50% 
in terms of the air-dry peat. The rapid increase in the higher 
terms is shown in the following table :— 
