130 — Transactions of the South African Philosophical Society. 
mended the use of citric acid for the extraction of both potash 
and phosphoric oxide, and, when the value of this method has 
been properly tested, it is possible that England also may fall into 
line with the other countries which have adopted standard methods 
of extracting available plant food from soils. : 
All will agree that, for agricultural purposes, an eae of 
a soil should show only those quantities of the constituents 
which are really available. That is exactly the ideal that 
the German and American chemists have been aiming at, and 
that Dr. Dyer is following up. To say that they have wholly 
succeeded would be asserting far too much; yet those who are so 
fond of decrying soil analysis aim all their shafts at a method which 
(though they know it not) has long been superseded, in Germany 
and the United States of America, by others whose object is to 
extract from the soil only those materials which plants themselves 
can take out. Some chemists have sought to do this in some ways, 
some in others, but a method of which Dr. Dyer’s is a modification 
has been used at Halle for determining available phosphates in soils 
years ago, and for this purpose such a method is now officially 
recognised practically the whole scientific world over. In brief, the 
principle of extracting available plant-food constituents is generally 
‘admitted amongst chemists of standing, the mode of applying this 
principle being the only point of difference. A few isolated persons, 
unaware of the progress made in the subject, are contending that 
the principle ttself 1s wrong, and the unfortunate thing is that many 
do not understand how wide of the mark the arguments employed 
really are. Here, too, to employ the critic’s boomerang, it may be 
said that ‘‘ one individual, often of no repute in the scientific world, 
resolutely and dogmatically takes the lead, and many follow, sheep- 
like, without inquiry.”’ 
A few words may be needed regarding the methods employed in 
our analytical investigations of the Colony’s soils, and first of all the 
collection of the sample requires attention. While travelling about 
the Colony collecting soils we have frequently been asked to include 
in our list soils from cultivated lands on this or that farm; soils, 
therefore, that have been modified by various or repeated cropping— 
‘soils, moreover, that have been in all probability considerably altered 
by the use of manures. For the occupier of that little plot of land 
an analysis of such a soil will probably have some value, but.for the 
country at large, or even for the surrounding district, it is absolutely 
valueless. Such a sample is not typical of any extended area, 
because it has been altered by the agency of man, and, as Dr. Wiley 
observes, ‘‘ The physical and chemical analyses of soils are entirely 
