ORGANIC CONSTITUENTS OF THE SOIL SOLUTION 85 



incinerated. To the dishes containing the ash were added re- 

 spectively nitric acid, sulphuric acid, and hydrochloric acid in 

 slight excess, and the dishes again brought to dryness. Water 

 cultures for wheat seedlings were then prepared. 1 Into one was 

 introduced the given volume of manure extract; into another the 

 ash from an equal volume of the extract which had subsequently 

 been treated with nitric acid; and cultures with the ash which 

 had been treated respectively with sulphuric and hydrochloric 

 acid were similarly prepared. After ten days growth, the plants 

 from the several cultures were compared. The plants from the 

 cultures which contained the sulphates and the chlorides were 

 not materially different from the plants grown in the check 

 culture. The plants from the nitrate culture had larger shoots, 

 but shorter roots than the check plants. But the plants grown 

 in the culture to which the manure extract had been added direct- 

 ly had by far larger and better shoots and the roots were incom- 

 parably superior to those grown in any other culture, being 

 larger, thicker, better branched, clear, bright and translucent, and 

 very turgid, "very like the roots obtained in cultures to which car- 

 bon black or precipitated ferric oxide had been added. 



The results of this experiment, which has been repeated a 

 number of times, using manure extracts of various origins, leave 

 no doubt that it is the organic components of the manure which 

 produce the characteristic effects, for the ash culture contained 

 all and even more of the mineral constituents "available" in the 

 original extract, and the nitrate culture excluded any explana- 

 tion based on the nitrogenous content of the manure. This con- 

 clusion was supported by the results of another experiment. 



To a manure extract was added alcohol, which precipitated 

 most of the organic dissolved substances but very little of the 

 inorganic ones. The precipitated organic matter was filtered 

 off, dried carefully in a water oven to eliminate the alcohol, and 

 then taken up in sufficient water to equal the original volume 

 of manure extract. The filtrate containing the major part of the 



1 Further studies on the properties of unproductive soils, B. E. Liv- 

 ingston et al., Bull. 36, 1907, and 48, 1908, Bureau of Soils, U. S. Dept. 

 Agriculture. 



