110 EXPERIMENT STATION EECOED. 



p. 715). — The best results were obtained with the Liebig-Koch method for 

 peptoue. For the determination of the easily oxidizable part of the sulphur, 

 digestion with a saturated solution of chlorate of potash in nitric acid proved 

 the most valuable. 



The determination of sulphur and chlorin in the rice plant, Alice R. 

 Thompson (Jour. Amer. Chem. Soc, 35 i,191S), No. 10, pp. 1628-1634) .—Pre- 

 viously noted from another source (E. S. R., 29, p. 231). 



The determination of humus in heavy clay soils, W. Beam {Cairo Sci. 

 Jour., 7 {1913), No. 85, pp. 219-224). — In continuation of work previously re- 

 ported (E. S. R., 28, p. 19), certain soils were encountered which were difficult 

 to treat even by the method of washing with carbon dioxid. In looking for the 

 cause of this, it was found that the acid employed for the extraction of the 

 magnesium and calcium had a marked effect upon the rapidity of the subse- 

 quent filtration when the washing was done by water or carbonated water. 



With an increase in the strength of the acid, ithe difficulties in washing in- 

 creased. " The use on the other hand of a weaker acid than that of 1 per cent, 

 commonly employed, results in a marked advantage in this respect ; but it was 

 not found practicable, as a rule, to carry the dilution below 0.5 per cent . . . 

 since the extraction of the calcium and magnesium may be incomplete, the 

 proportion of humus found being, in such cases, below the truth. A still 

 further improvement was effected by substituting for the solution of carbonic 

 acid a very dilute solution of hydrochloric acid — about 0.02 per cent." The 

 use of such dilute hydrochloric acid for the washing makes the method 

 applicable to all classes of soils with ease and certainty. 



Working with soils from the Nile no marked differences were noted in the' 

 results when ammonia up to a strength of 16 per cent was used (E. S. R., 

 24, p. 9), providing the soils were in a properly flocculated condition. When 

 this is not the case, a stronger ammonia may lead to higher results; the 

 proper humus figures can only be obtained after repeated extraction with 

 ammonia. The author prefers 4 per cent ammonia. Although the filtrate ob- 

 tained is quite clear in the method recommended by the author, it is deemed 

 advisable to add 0.5 gm. of ammonium carbonate as suggested by Rather 

 (E. S. R., 25, p. 614) to each 100 cc. of the ammoniacal solution. If ammo- 

 nium carbonate is employed in too large amounts, the figures will be far 

 below the truth. " It is interesting to note that if in the modified official 

 method the washing out of the acid is effected by the use of 0.02 per cent 

 hydrochloric acid, practically the whole of the chlorid in the ammoniacal 

 extract is carried down with the clay when the solution is treated with ammo- 

 nium carbonate." 



The humus in the soils of the Sudan can be very accurately estimated by the 

 colorimetric method. " In the case of soils of approximately the same com- 

 position as regards proportion of clay and humus the latter may be deter- 

 mined by direct boiling with 0.5 per cent sodium carbonate solution, preferably 

 after previous boiling with distilled water in order to disintegrate the soil. 

 Five gm. of the latter is treated with 400 cc. of distilled water in an enameled 

 iron vessel and boiled for five minutes; 20 cc. of a hot solution containing 2.5 

 gm. of sodium carbonate is then added and the boiling continued for exactly 

 one minute. The liquid is cooled as rapidly as possible, made up to 500 cc, 

 and allowed to stand over night in a covered beaker. If not perfectly clear 

 the supernatant liquid is filtered through an asbestos filter. A small Buchner 

 funnel is suitable. The comparison is made with a similar soil of known humus 

 content treated in the same way. 



"The most accurate results are obtained by treating the soil with acid, as 

 in the gravimetric determination, followed by extraction with ammonia. The 



