EXPERIMENT STATION RECORD. 



Vol. XXXI. Abstract Number. No. 9. 



RECENT AVORK IN AGRICULTURAL SCIENCE. 



AGRICULTTJRAL CHEMISTRY— AGROTECHNY. 



Ammonia-soluble inorganic soil colloids, G. S. Fraps {Texas Sta. Bui. 165 

 (1914), pp. .3-8). — It is pointed out that the indirect methods do not really 

 estimate the colloidal constituents of soils but only compare them with regard 

 to certain properties which may be partly dependent on other soil constituents. 

 " The only method as yet proposetl for approximately estimating the total 

 colloids is by staining the colloidal particles, and estimating their number 

 or quantity by means of a microscopic examination." 



The work reported in this bulletin deals with the soluble colloidal soil sub- 

 stances and not with the total, or insoluble, colloids. The method used is based 

 on observations made in the laboratory of the Texas Station, that when am- 

 monium carbonate is added to the clear ammoniacal filtrate obtained in digest- 

 ing soils with ammonium hydroxid a precipitate consisting chiefly of inorganic 

 material is obtained. " The use of ammonium carbonate for precipitating the 

 clay is the method proposed by Rather [E. S. R., 25, p. 614] for purifying the 

 ammoniacal humus filtrate." The method is as follows: 



" Digest 100 gm. of the soil with 2,000 cc. of fifth-normal hydrochloric acid 

 at room temperature for 24 hours. Filter and wash thoroughly. Wash back 

 into the bottle with 2,000 cc. of 4 per cent ammonia and let digest at room 

 temperature for 24 hours, shaking every half hour for 4 hours. Filter on a 

 large folded filter, getting as much of the soil as possible on the filter, and 

 continue to pour back' the filtrate until it comes through clear, as per the Smith 

 method. Discard the residue. Take 1,500 cc. of the filtrate, coagulate with 

 the ammonium carbonate (and heat, if necessary), let settle, collect on ash- 

 free filter, ignite, and weigh. 



" Fuse the precipitate with sodium and potassium carbonate, dissolve in 

 hydrochloric acid, and evaporate to render silica insoluble. Filter off and 

 weigh silica, if pure; if contaminated with iron, purify. Precipitate the iron 

 and alumina in the filtrate with ammonia, ignite, and weigh precipitate. Fuse 

 with potassium acid sulphate, and dissolve, reduce the iron with zinc, and 

 titrate with iDermanganate." 



If the soil contains much lime several extractions must be made with the 

 hydrochloric acid or with stronger hydrochloric acid for the purpose of remov- 

 ing it. 



The soils to be examined are divided into four groups, arranged according 

 to their total content of ammonia-soluble colloids, viz, " (1) to 0.05 per 

 cent; (2) 0.051 to 0.101 per cent; (3) 0.101 to 0.2 per cent; (4) 0.201 to 0.6 



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