410 EXPERIMENT STATION EECORD. 



The method of procedure iu the experimental work was in general as follows: 

 " The mineral, finely ground in an agate mortar, was left several days at room 

 temperature, with occasional shaking, in a well-stoppered flask with twice its 

 weight of the solution. Whether contact was for a few hours or a few months 

 made little difference. The liquid was filtered through a double layer of filter 

 paper in a Gooch crucible, which, except in the case of pure-water extracts, re- 

 tained the finest powders and gave perfectly clear filtrates. A measured quan- 

 tity of the filtrate was subjected to analysis. After addition of acid, silica was 

 removed by evajToration, iron and aluminum were precipitated with ammonia, 

 and calcium was separated with ammonium oxalate. Ammonium salts were 

 then driven off by heating, and magnesium was precipitated and washed with 

 barium hydroxid solution and weighed as the sulphate. The barium hydroxid 

 contained a trace (less than 0.1 per cent) of impurity, chiefly potassium and 

 sodium, for which a correction was applied iu the one or two cases in which it 

 was of significance. In the filtrate from magnesium hydroxid barium was pre- 

 cipitated with ammonium carbonate, reprecipitated, and the alkalis in the 

 filtrate were weighed as chlorids and separated in the usual way. Repeated 

 tests of the alkali chlorids for magnesium gave, as a rule, an unweighable trace 

 at most — rarely a few tenths of a milligram." 



The determination of numic acid in soils, G. H. Coops {Chem. Weekbl. 

 J, (1907). PI). 315-S21; aljs. in .Jour. Chcm. Soc. [London], 92 (1907), No. 537, 

 II, p. 590). — The method employed was as follows: Boil about 10 gm. of the soil 

 repeatedly with absolute alcohol, recovering the bulk of the alcohol by dis- 

 tillation and restoring the original volume by addition of water (Freseuius's 

 method). Filter off the solution containing the soluble humic acids from the 

 waxy and resinous matters and titrate with tenth-normal barium hydroxid. 



" The precipitate fox'med, which may be converted into barium sulphate, repre- 

 sents those humic acids which form insoluble barium compounds. The filtrate 

 on addition of sulphuric acid yields a further quantity of barium sulphate rep- 

 resenting soluble barium salts of humic acids. The residue from the alcoholic 

 extraction contains other humic acids. It must be remarked, however, that 

 humic compounds are present, which under the influence of alkalis gradually 

 yield additional humic acids." 



Heat the mass with addition of a little water on the water-bath for half an 

 hour, with careful addition of teuth-uormal potassium hydroxid until neutral. 

 Filter the solution and wash the residue a few times (this is much assisted by 

 centrifugal action), and then digest with an equivalent amount of tenth-normal 

 sulphuric acid, uniting the two extracts. As a check, mix one-half of the solu- 

 tion with a saturated solution of potassium sulphate, thus precipitating certain 

 humic- acids, and titrate the filtrate with tenth-normal potassium hydroxid. 

 Shake the other half well with ether, which removes any colloidal silica as an 

 emulsion. After submitting to centrifugal action siphon off the bottom layer 

 and divide it into three portions. Mix one of these with a saturated solution 

 of potassium sulphate, and titrate the filtrate witt tenth-normal potassium 

 hydroxid. Titrate the second portion with tenth-normal barium hydroxid. Con- 

 vert the soluble and insoluble barium salts formed into sulphate and weigh. 

 Carefully neutralize the last portion with tenth-normal potassium hydroxid and 

 precipitate with ferrous ammonium sulphate, collecting and weighing the pre- 

 cipitate, which, allowing for the iron oxid contained therein, represents gallic 

 acid derivatives. Finally calculate all results on air-dry and ash-free soil. 



Extracting' with citric acid as a means of determining the fertility of soils, 

 S. Frankfurt and I. Novikov (Vi/rstnilc ,sv//,-7i. Proniids]!., 1906, Xos. .'/6, 

 pp. 721-726; .',7, pp. 758-765; 48, pp. 801-808; 49, pp. 838-81,6; abs. in Zhiir. 

 Opuitn. Agron. [Russ. Jour. E.vpt. Landw.], 8 (1907), No. 2, pp. 2.',9, 250).— 



