BESEAKCH METHODS IX STUDY OF FOREST ENVIRONMENT. 131 
})aper filter, in a 6-inch funnel, and the water is poured on to it. a 
few cubic centimeters at a time, through a period of 24 hours. Be- 
fore the soil has thoroughly settled, some clay is likely to pass 
through the filter. This is eliminated by pouring on to the soil a 
second time the first 100 cubic centimeters of water which passes 
through. When all of the water has drained out, the solution may 
be partly boiled away and allowed to cool, when the suspended 
matter will largely flocculate and may be removed by a second fil- 
tering. The clear solution is then evaporated in a weighed, por- 
celain dish. Solutes varying in amount from 20 to 1,500 parts per 
million of the soil weight are ordinarily found in such extracts. 
This subject has been investigated in great detail by King (129). 
For the purpose of ecology, qualitative analyses showing the pres- 
ence in some quantity of the elements and compounds known to be 
essential, may often be all the chemical evidence that is required to 
throw the burden upon some other environmental condition. Fol- 
lowing Osborn (135), who has rather recently given a summary of 
the evidence on this subject, the investigator may look for: 
1. Nitrogen (in the form of nitrates), as an essential constituent 
of proptoplasm, required in large quantities when the proteins are 
being produced, as in seed formation. Nitrogen is itself practically 
useless without nitrifying agencies in the- soil, so that the presence 
of humus is not absolute proof of the abundance of nitrates. 
Nitrogen in certain forms may also, as shown by Schreiner and 
Skinner (138), inhibit plant growth. This is a subject of great 
complexity. 
2. Phosphorus, as an essential of the nuclei of cells. 
3. Iron, as an essential of protoplasm, and playing an important 
part in the formation of chlorophyll. A lack of iron in available 
form is quickly shown in yellowing or " chlorosis " of foliage. 
1. Magnesium, as a constituent of the chloroplasts. 
5. Sulphur, required for forming proteins. 
6. Potassium, probably as a regulator of life phenomena through 
chemical reactions. 
7. Chlorine, commonly present in plants and probably functioning 
in metabolism. 
It is with a view to detecting the lack of some of these substances 
that the following simple tests are enumerated, requiring the mini- 
mum of laboratory equipment and technical skill. 
The sample of air-dried soil which is to be examined should be 
placed in a glass jar and distilled water added to the amount of five 
to eight times the volume of the soil. After about five minutes the 
solution may be used. 
One hundred cubic centimeters of the solution may be tested 
qualitatively for chlorine. For this purpose, to the soil solution 
