RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY— AGROTECHNY. 



The acids and colloids of humus, G. Fischke {Kilhn Arch., 4 {1014), PP- 

 1-136, figs. 4)- — In this work the colloids of humus were isolated by either the 

 cold or hot water extraction metliods, with filtration through hardened quantita- 

 tive filters, asbestos or Pukall's filters, and concentration in vacuum at 30° C. 

 or at ordinary pressui'e. The concentrates were purified by either parchment 

 paper or fish bladder, by ultrafiltration, precipitation with alcohol, acetone, etc. 



The method of preparing the humus did not seem to have any effect upon the 

 reactions, but it has not been established whether the hot-water treatment can 

 be used in other instances. On account of the higher concentrations of the Pukall 

 filtrates of the hot-water extracts, the observations could be more easily made 

 on these solutions. 



The colloids of the cold-water treatment of composts in some cases showed 

 other reactions. Humus colloids passed through 7.5 per cent ultrafilters. The 

 colloids remaining in the ultrafilter with one exception were irreversible, but 

 the ultrafiltrates still contained typical colloids, as was proved by flocculation, 

 cataphoresis, and ultramicroscopy. 



The hydrogen ion concentration of the various soils examined was determined 

 by direct measurement of the electromotive power on the nonpurified and 

 dialized solutions of humus. The crystalloid cations were removed from the 

 colloid salt by dialysis. No illusion of an acid reaction with an indicator like 

 litmus which depends on the absorption of the coloring matter cations could be 

 noted. 



Migrating capacity and velocity were determined v/ith and without the addi- 

 tion of acid or alkali in unpurified and dialyzed colloids. The electric charge 

 was negative, and the migrating velocity was least in acid media. Black soils 

 were not examined. The migrating velocity of the dispersive phase of the same 

 solution was ununiform, and the electric potential of the colloid particles was 

 not constant. 



By covering with water in the modified Coehn apparatus, partial coagulation 

 occurred. This was irreversible in unpurified colloids, with one exception, but 

 i-eversible after purification. 



Protective properties were not possessed by humus colloids against colloidal 

 gold and clay. There was protection against iron oxid, but it was not identical 

 with that of reversible colloids. Reduction of colloidal iron oxid by humus 

 colloids was not observed. The precipitation optimums of humus sols and 

 sesquioxids were, in some cases, established. The humus colloids were not 

 sensitive toward electrolytes. Reduction of gold chlorid hydrochlorid in the 

 presence of humus was not noted. The dry state of humus sols in soils in most 

 cases was irreversible. 



A chemical analysis of the inner organic constituents of the soil in most cases 

 gave no insight into the composition of colloids, but only emphasized the organic 

 nature of humus colloids. Microscopically examined, the solutions of colloids 

 were found homogeneous. Greenish-yellow and yellowish-red particles were 

 visible with the ultramicroscope. Humus colloids were not found to be typical, 



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