AGRICULTURAL CHEMISTRY AGROTECHNY. HI 



removal of the excess of hydrochloric acid is of course not necessary. Using 

 this method the comparison may be made between soils of greatly varying 

 composition both as regards clay and humus." 



The influence of ammonium carbonate upon the determination of humus. — 

 A rapid and eflB.cient filtration procedure, W. II. MacIntire and J. I. Hardy 

 (Tennessee Sta. Bid. 103 (1914), pp. 47-76, figs. 2).— In this work the authors 

 have modified the Rather method (E. S. R., 25, p. 614) by reducing the am- 

 monium carbonate required to 1 gm. and filtering the entire mixture imme- 

 diately after adding the carbonate and after the 36-hour period in which the 

 soil was in contact with ammonia. The Buchuer funnel and suction were 

 used in the operation. By the use of this apparatus, etc., the time of filtration 

 of the humus extract is shortened. While the introduction of the ammonium 

 carbonate accelerates filtration, extra care must bo exercised to shake the 

 mixture gently after the addition of the carbonate, otherwise filtration is 

 retarded. 



As a filtering medium the soil itself is preferred. Although sand when 

 added to the soil at the time of filtration increases the speed of filtration, the 

 results obtained with it are not uniform. The modification recommended 

 reduces the amount of ash obtained. The results obtained with the modifica- 

 tion are more ;u accord with those yielded by the Smith and Mooers-Hamptou 

 methods than by the Rather method. No sediments were found in the humus 

 solution after standing for six months. If the soil is allowed to stand in 

 contact with the ammoniacal solution containing carbonate a change in the 

 humus content of the solution takes place. 



" Because of the two distinctlj- opposite influences of ammonium carbonate, 

 and occlusion effected, the period of contact of soil with carbonate is an 

 important factor, and in the modification is reduced to the minimum. The 

 decrease in humus resulting from the addition of carbonate can not be attrib- 

 uted to lessening of alkalinity. There is no chemical precipitation from the 

 humus solution effected by the addition of ammonium carbonate. There is no 

 fixation of carbonate, chemical or mechanical, in the solution free from contact 

 with the soil. The physical effects (occlusion) of 25-gm. charges of normal 

 carbonate and acid carbonate of ammonia and mixtures of the two salts are 

 greater than their solvent action in both water and ammonia solutions, the 

 reverse being the case with the smaller treatments. Twelve-hour contact with 

 4 per cent ammonia converted all acid carbonate in the three amounts used to 

 normal carbonate, but 2-hour contact does not convert all of the bicarbonate 

 in 2^- and 25-gm. charges of the salt. 



" Pure clay may be easily filtered immediately by the modified proced- 

 ure. . . . 



"A solution of the black meadow soil was not freed from excess of iron by 

 the later modification suggested by Rather. Ammonium sulphid removed both 

 iron and organic matter from ammonia solution. Carbon bisulphid eliminated 

 iron without any apparent effect on the organic matter of the ammonia solu- 

 tion. In such unusual cases where the ash is shown to be due to Fe2(OH)6 in- 

 stead of to clay the application of a correction of 33 per cent is sug- 

 gested. . . . 



" Repeated digestions and filtrations by the 1-gm. modification uix)n the same 

 soils have given solutions practically identical in analysis. It is emphasized 

 that the original official method directs the use of 4 per cent NHs instead of 

 4 per cent NH4OH, as is erroneously given in Bulletin 107 (rev.) of the 

 Bureau of Chemistry." 



