106 EXPERIMENT STATION KECORD. 



cussed. With the precanlions prescribed the method is considered absolutely 

 exact for the purposes ju'oposed. 



On the determination of sulphuric acid as barium sulphate, E. Ruppin 

 (Chem. Ztff., 33 {1909), No. 3, pp. 17, IS; abs. in Chem. Zentbl., 1909, I, No. 7, 

 pp. 577, 578). — The author i)oints out that it is difficult to obtain accurate 

 results in the precipitation of sulphuric acid by means of barium chlorid in 

 the presence of large amounts of chlorids. As a result of a study of various 

 methods, he concludes that accurate results can be obtained by precipitation in 

 acid solution with a large excess of 10 per cent barium chlorid, the occluded 

 barium chlorid being removed by repeated boiling. 



The determination of sulphuric acid as barium sulphate, J. F. Sacher 

 {(niem. ZUj., 33 {1909), No. J.j, pp. 218, 219; <ib.-i. in Ztschr. Angcw. Chem., 22 

 {1909), No. 15, p. 685; Chem. Zentbl., 1909, I, No. 14, p. 1195). — Referring to 

 Ruppin's statement, noted above, that the precipitation of sulphuric acid in 

 solutions containing a large amount of chlorids does not give exact results by 

 ordinary methods, the author states that accurate results can be obtained by so 

 controlling conditions as to secure slow precipitation in dilute solutions. He 

 obtained best results when about 0.1 gm. of barium sulphate precipitate was 

 obtained to each 100 cc. of solution. 



The determination of sulphuric acid as barium sulphate, E. Ruppin ( Chem. 

 Ztg., 33 {1909). No. 'i3--'i'i. P- 398). — Commenting upon Sacher's method of 

 precipitation in very dilute solution, noted above, the author points out that 

 under such conditions solubility of the barium sulphate plays an important 

 role. His studies of the method indicate that a correction of 2.r> mg. per liter 

 of solution should be used. 



On methods of clay analysis, A. Atterberg (A. Laudtbr. Akad. Handl. och 

 Tidskr., Jf7 {1908), No. 5-6, pp. 365-397, figs. 8). — The methods of mechanical 

 clay analysis proposed by earlier investigators are reviewed and the results of 

 the author's studies bearing on classification of clays are given. 



A method is tentatively recommended for the separation of clays into 6 natu- 

 ral groups, ranging from very stiff clays to sandy moor clays and so-called 

 '■ mjun " clays. After a preliminarj^ examination the dry pulverized sample is 

 carefully examined under the microscope, and a "rubbing test" made of a 

 cake of the clay that has been dried at 100° C. The mechanical analysis is 

 preceded by boiling or shaking the sample with water if it is high in calcium 

 carbonate and clay colloids but low in humus. If it is high in both calcium 

 carbonate and humus, the latter is oxidized by digestion with sodium hypo- 

 bromite solution (50 cc. bromin to 500 cc. of 20 per cent soda solution) in the 

 cold for 24 hours. If the sample is low in or free from carbonates, or the fine- 

 ness of the carbonates is not to be determined, the following method of pro- 

 cedure is adopted : 



Twenty gm. of the sample is first treated with 100 cc. hydrochloric acid 

 (sp. gr. 1.12) in a boiling water bath for an hour; the solution is made up 

 to 508 cc. with distilled water (volume of soil sample 8 cc), and then shaken 

 and left to settle; the clear solution is decanted and the last portion filtered 

 off ("hydrochloric-acid-solution A"). The residue is heated for 3 minutes with 

 20 cc. of a 20 per cent soda solution ; then cooled and diluted to 508 cc, mixed, 

 left to settle, and the clear solution decanted (" sotla-solutlon B"). I'he 

 residue is now elutriated in a graduated cylinder of si)ecial construction, and 

 separated into coarse clay (0.02-(7.002 mm.) and fine clay (less than 0.002 mm. 

 in diameter), the quantities jiresent of each portion being ascertained by 

 weighing the dried residues. The hydrocliloric-acid-soluble clay is determined 

 in .50 cc. of solution A and 50 cc. of solution B by addition of a little nitric 

 acid ; diluting and heating in a covered beaker ; ammonia is added gradually 



