RESEARCH METHODS IN STUDY OF EOREST ENVIRONMENT. 131 



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, qualiative 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 protoplasm, 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. Ni- 

 trogen 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 foilage. 



4. 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 

 should be added one or two drops of potassium chromate (K 2 Cr 2 4 ) 

 solution and titrated from a dropper by a weak solution of silver 



