436 
CORRESPONDENCE. 
EcoLoGIcaL METHODS OF SOIL ANALYSIS. 
Mr. W. B. Crump’s reply to my criticism? has certainly elucidated 
many points which were somewhat obscure in the original abstract, but, 
unfortunately, Mr. Crump entirely overlooks the main point with regard 
to the ‘‘ water-content ” figures given by the authorities he quotes. 
It is very evident from the table of results for four distinctive soils 
given by A. D. Hall in his standard work ? that there is something 
“more than a verbal difference’ between ‘ water absorbed ’ by 100 parts 
of dry soil to make it moist and the ‘ water-contained ’ per cent. in that 
moist material. Further it will be noticed that it is only in the ‘ water- 
absorbed’ column that the figures approximate and occasionally exceed 
100. 
There are three recognised forms for expressing ‘ water-capacity ’"— 
(a) ‘ Water-absorbed’ by 100 parts of dry sample (100°C.). 
(b) Percentage by weight of water in sample. 
(c) Percentage by volume of water in sample. 
The first method is the least satisfactory and its only redeeming 
feature is that it entails the consideration of but one variable quantity, 
viz., the water. This method is very useful when one wishes, for instance, 
to record changes in the humidity of peats over a long period, for obviously 
in the other forms as the water increases the percentage of the dry con- 
stituents decreases, thus making ready comparisons somewhat difficult ; 
unfortunately the figures above 30 or 40 per cent. become unduly large 
when compared with the results given by the other methods.* The 
soundest idea of the actual state of affairs is perhaps given by (c) but this 
entails considerable additional labour, whereas in (b) —the form suggested 
by the writer—the results are not liable to any misconstruction, as it will 
be seen that the same figure serves both for ‘ water-capacity ’ and ‘ water- 
content,’ on the other hand the figures given in the abstract should be 
severely restricted to ‘ water-absorbed ’ and their use as ‘ water-content ’ 
is not only scientifically incorrect but also an outrage on the common 
acceptance of the term ‘ content.’ 
Reference to the later analytical results given by Mr. Crump? still 
further illustrate the confusion occasioned by the mis-use of this term. 
Thus soil No. 172 is stated to have a water-content of 24.8 per cent. ; 
immediately following this is a ‘ Loss at 100° C.’ of 5.92 per cent. This 
latter is really the moisture® or true ‘ water-content ’ of the air-dried soil. 
The presence of two different ‘ water-contents ’ in the same soil is certainly 
still confusing, if not paradoxical, even though covered by a guise of 
terminological differentiation. The most unfortunate part of the reply, 
however, is where Mr. Crump fails to unravel the tangle on page 170 and 
then imputes to me certain vindictive intentions whereas I merely wished to 
suggest that the ‘convenient method’ given for estimating the humus 
humus 
content, 1.é., was obviously incorrect, and that it was most 
mineral 
probably a slip or printer’s error. The defence of this equation involves 
the accuracy of the whole paper, for whereas formerly ‘ water-content’ 
had been confused with ‘ water-absorbed’’ ratio—with percentage com- 
position amounts, etc., etc., we now find that the cardinal point of the 
whole paper—humus-content—rests on uncertain ground. 
With regard to the abstract nature of the paper criticised, I have been 
——— nel 
1 The Naturalist, 1913, pp. 239-241. 
2 The Soil, Second Edition, page 69. 
3 The Natural/st, page 169, 1913. 
4 The Naturalist, page 241, 1913. 
5 The Soil, Second Edition, Appendix I., page 300. Analyses of 
typical soils. 
Naturalist, 
