CHEMISTKY. 745 



dropping funnel until the tip of the glass tube, for the introduction of air, is covered. 

 When this point has been reached, and if no very vigorous action is taking place, 

 the combination flask is slowly heated until the sulphuric acid commences to give off 

 fumes. It is held at this temperature for from 5 to 10 minutes, and then allowed 

 to cool slowly, unless there is reason to believe combustion has not been complete, 

 in which case the temperature is again raised. Care must ])e exercised to see that a 

 steady current of air be kept passing through the apparatus, and that the mixture in 

 the fiask be not forced back toward the wash-bottles. ' ' 



In case of soils containing chlorids this method of procedure may result in the 

 generation of chlorin gas, which will vitiate the results. This, it is claimed, may be 

 obviated ])y dissolving the potassium bichromate in the concentrated sulphuric acid 

 and slowly and cautiously running the solution in upon the soil with no attempt to 

 heat the mixture until the reaction in the flask has proceeded for some time. By 

 proceeding in this manner "no hydrochloric acid, chlorin, nor chromyl chlorid gas 

 is generated, or in but very small amounts. The procedure thus modified has been 

 used a large number of times with artificial mixtures and natural soils, and has 

 proved satisfactory, although no explanation is obvious why hydrochloric acid should 

 not be formed and oxidized under these conditions." The method is claimed to be 

 fairly rapid, a combustion requiring on the average about 40 minutes. 



As a result of a large number of determinations, it is stated that the organic matter 

 in a subsoil rarely equals or exceeds that contained in the corresponding soil. "The 

 facts presented here would suggest that the humus determination is of even more 

 uncertain value than is usually believed. There is not sufficient ground as yet for 

 advocating the use of any other factor than the usually accepted one [0.471] for the 

 calculation of the organic matter from the carbon dioxid obtained in the combustion." 



A number of determinations are reported which show an average of 42 per cent of 

 carbon in humus instead of 56 per cent, as reported by other investigators. 



On the determination of assimilable plant food by extraction of soils with 

 very dilute acids, H. G. Soderbaum (A'. Landt. Akad. Handl. och Tidskr., 43 {1903), 

 pp. 103-106; abs. in Centhl Agr. Chem., 32 (1903), No. 13, pp. 795-75'<?).— This is an 

 account of pot experiments during 1900 and 1901 with barley growing on loam and 

 humus soils which had been extracted for 48 hours at ordinary temperatures with 

 2 per cent hydrochloric acid. The extracted soils without addition of any fertilizing 

 material proved practically sterile. The application of lime as carbonate, however, 

 resulted in a partial restoration of the productive capacity, and wdth api:)lications of 

 lime and 2 of the essential fertilizing constituents (either potash or phosphoric acid) 

 the yield was very little less than that on unextracted soil. Apparently assimilable 

 nitrogen was the element most completely removed by the extraction, but in no case 

 did the treatment remove all of the assimilable plant food present in the soil. 



A contribution to soil analysis, O. Forster {Chem. Ztg., 28 {1904), No. 4, pp. 

 36-38). — A method of procedure is described which is intended to obviate as far as 

 possible the difficulties encountered in securing complete removal of solution from 

 the insoluble residue of acid digestion, and also the separation of potassium and 

 alkaline earths from the voluminous iron and alumina precipitates. 



The solution is prepared by treating 100 to 200 gm. of the air-dry soil for 3 hours 

 on a water bath with 10 per cent hydrochloric acid at the rate of 2 cc. of acid to each 

 gram of soil. The solution after cooling is diluted with water at the rate of 1,000 cc. 

 for each 100 gm. of soil, and an aliquot part of the solution is evaporated to dryness 

 with 5 to 10 cc. of nitric acid to remove silicic acid. The residue is taken up in dilute 

 hydrochloric acid and the solution diluted to such a volume that each 100 cc. cor- 

 responds to 40 to 50 gm. of soil. Aliquots corresponding to from 20 to 50 gm. of soil 

 are used for the determination of phosphoric acid, potash, lime, and magnesia by 

 methods which are described in detail. 



