CuZ+ reacts with fulvic acid to form a site-bound chelate on the fulvic acid polymer molecules. It is deduced from literature evidence that this chelate is the same type that Cu2+ forms with salicylic acid. This is supported by a Job's continuous variations plot. The mass action quotient for the chelate formation in 0.1 172 KC1 at 25.0 "C has been measured as a function'of the degree of ionization of the chelating carboxyl groups. The strength of the Cu2+ -fulvic acid chelate is comparable to that of other bidentate Cu2+ chelates.

Organic matter extracted from O2 and Bh horizons of a Podzol soil was pyrolyzed between room temperature and 540°C. Samples were withdrawn at regular temperature intervals and analyzed by chemical and spectroscopic methods. The carbon content of the chars increased with temperature accompanied by a simultaneous decrease in oxygen. The chars of both organic matter preparations heated to 540°C. contained identical percentages of carbon and hydrogen but no oxygen. Some of the nitrogen and sulfur in the original organic matter was very stable and was recovered in the chars heated to the highest temperature. Phenolic OH groups were more stable than COOH groups but both were eliminated between 250° and 400°C. Both types of functional groups were more stable in the Bh horizon organic matter than in O2 horizon organic matter, apparently because the former was more aromatic. The infrared spectra of the chars were in general agreement with the chemical data. On the basis of the analytical data the low temperature peaks in the DTG curves of both organic matter preparations were due mainly to the elimination of functional groups, whereas the high‐temperature maxima resulted from decomposition of the nuclei. Using the graphical‐statistical method of Van Krevelen, the main reactions governing the pyrolysis of O2 horizon organic matter were found to be: (a) dehydrogenation (up to 200°C.); (b) a combination of decarboxylation and dehydration (between 200 and 250°C.); and (c) continuous dehydration. The main reaction determining the pyrolysis of Bh horizon organic matter was dehydration.

No abstract

Differential thermogravimetric (DTG) curves of untreared peat, muck, and 10 different Podzol L-H materials showed peaks ac approximately 100" C (moisture), 280' (low-temperature band), and'170 to 390'' C thigh-t"-perarure band). The maxima at 2-80' C wcre sharp and clraracterisric-of all^surface materials investigated. The DTG curves lr'ere essentially rhe same for all of the Podzol L-fimaterials investiEated.The DTG curves for 12 orean-ic matter DreDarations exffacted from Podzol Bh, Bfh, Bhf, Bfl, and Btf hoiizons showed maxima at 100' C arrd in the 420 to 520'C region (high-temperarure band). The peaks at 280" C were virtually absent in thEse matirials. This suggcsted differences in composition between [-H and B horizon orsanic mattei-of the Podzols srudied. The variations in the positions of the hig-h-temperature bands of the B materiais were related to the nrorphological characteristics of these soils in the 6eld. From this it appeared that thermogravimetry might be a useful aid in soil classification.Addition of inorganic materials did not affect the position of the low-temperature bands but had a pronounced effect on the high-temperature bands of both L-H and B organic matter. Addition of Na caus6d the ieaks of the latter to shift to hiqher iemperatures rvhile addition of Al and Fi car:sed shifts to lou'er temperitures, INTRODUCTIOIIIn previous publications (3, 5), DTG (differential thermogravime ric) curves for organic matter originating from the I-H and Bh hdrizons of a Podzol were presented. The Jurves 5f ttte rwo materials were quite different.Above 100' C, where water was lost. the L-H material sliowed two distinct bands, a rather broad one with maximum at 280' C and a narrower one with a peak at 5200 C. The DTG curve of the Bh material, on tl-re other hand, yielded only one distinct peak at +2o" .C. The latter material shou'ed a slorv but more oi less constant iate of weighr loss berween l25o and 350" C.The distinct difference found between the DTG curves of the L-H and Bh organic matter of a single Podzol profilc raised the quesrion whether ol not this w-as characteristic of Fodzols in seneral. With this in mind. a studv was made of the thermogravimetry of i-H and B horizon organic matter of Podzols from 10 different sites'. For comparative purposes, one sample each of peat, muck, and lignite u'as included in the survey. APPARATUS A Stanton recording thermobalance of 0.1 mg sensitiviry was used and the samples were held in platinum crucibles. f constant rate of heating (5.5' Czmin) was maintained. Thermogravimetric (TG) curves were obtained by replotting thermogravirnetric iata as weight loss'(Y-axis) vs. temperature (X-axi:). ftle weight change per 2.5 minute inteffal as obtained by simple difference was plotted vs. temperature to give differential thermogravimetric (DTG) curves.

A precise, accurate, and comparatively rapid fluorometric method for the determination of selenium in the nanogram range is described and results are presented for Youden's uniformity and ruggedness tests. The sample is digested in a nitric-sulfuricperchloric acid mixture, potential interferences are masked with disodium EDTA, and selenium is complexed with freshly-prepared 2,3-diaminonaphthalene solution and estimated fluorometrically after extraction into cyclohexane. On the basis of its performance, collaborative study of the method is recommended