610 EXPERIMENT STATION RECORD. 



reversible hydrosols, but appear to be related to certain organic coloring 

 matters. 



A new reaction for clay, F. Rathgen (Tonindus. Ztg., 38 {19 H), No. 3, pp. 

 SO, 31, fig. 1; abs. in Chem. Ztg., 38 {19U), No. U, Repert., p. 57).— This is a 

 microchemical reaction wbich will detect aluminum and aluminum compounds 

 in all substances, even though they be present in traces, e. g., in green or brown 

 bottle glass. To 1 gm. of the powdered substance under examination in a 

 platinum dish is added a little ammonium fluorid and 4 to 5 drops of concen- 

 trated sulphuric acid, and heated gently to dryness. As a result corundum is 

 formed, which may be recognized under the microscope as six-sided colorless 

 plates. When iron is present there are formed yellowish to brownish six- 

 cornered crystals surrounded by a border of colorless corundum. Light-green 

 (very small) and bluish six-cornered crystals point to the presence of cobaltic 

 and chromium oxid, respectively. 



A review and discussion of some of the methods for the determination of 

 alkali in soils, R. F. Hake (New Mexico 8ta. Bui. 95 (1915), pp. 7-i6).— This is 

 the report of the associate referee on alkali soils to the Association of Official 

 Agricultural Chemists at Washington, D. C, November, 1914 (E. S. R., 32, p. 

 296). It reviews and discusses methods used by the Bureau of Soils of this 

 Department and by several of the state experiment stations for the determina- 

 tion of alkali in soils. 



Comparative investigations of Thomas slag powders according to the 

 Lorenz, Naumann, and Popp methods, W. Hoixe {Chem. Ztg. 38 {1914), Nos. 

 112-113, p. 1083). — In these investigations it was found that the Lorenz method 

 gave lower results than the Popp and Naumann methods, the two last-named 

 methods being considered about on a par. The best results can be obtained 

 by the Lorenz method, but the procedure is cumbersome. See also the work 

 of Haussding (E. S. R., 31, p. 410). 



Methods of bacterial analyses of air, G. L. A. Ruehle {U. S. Dept. Agr., 

 Jour. Agr. Research, 4 {1915), No. 4, pp. 343-368, figs. 3).— This study was 

 undertaken at the New York State Experiment. Station in connection with the 

 relation of the bacterial content of stable air to the amount of bacterial con- 

 tamination of milk. It is devoted especially to a detei'mination of the Altering 

 efficiency of two aeroscopes and a modification of one of them. 



" It seems reasonable to conclude that the nature of the filters tested had 

 little influence on the results secured in duplicate analyses, that is, those ob- 

 tained where a sand and a liquid filter were used side by side agreed just as 

 well as those where either two sand filters or two liquid filters were used side 

 by side. It was found that the particular form of sand-filter aeroscope recom- 

 mended by the committee on standard methods of bacterial air analysis ap- 

 pointed by the American Public Health Association varied in its filtering effi- 

 ciency from 50 to 100 per cent, with the average efficiency for two series of 

 tests of 90 and 91.6 per cent. It is believed that the chief cause of error with 

 this form of aeroscope arises from the fact that it is so constructed that it must 

 be sterilized with steam, which causes caking of the sand-filtering layer." 



The modification of the standard aeroscope differs from the standard instru- 

 ment in that the lower rubber stopper and the bolting cloth supports are elimi- 

 nated and the small tube is fused into the larger one. The layer of sand is 

 supported by a layer of cotton, resting on the shoulder at the junction of the 

 large and small tubes. The upper stopper is replaced by a cork, which permits 

 sterilization of the aeroscope by dry heat instead of steam. 



" The modified standard aeroscope was found to retain nearly 100 per cent 

 of the bacteria, with little chance of error. It was also found to be cheaper. 



