AGRICULTURAL CHEMISTRY AGROTECHNY. 503 



" Starch paste with potassium iodid is not a suitable reagent for studying 

 oxidases because hydrogen peroxid alone or organic peroxids set free active 

 oxygen under these conditions. Bleaching of blued guaiacum is not due to 

 reducing substances but to inhibiting effect of hydrogen peroxid on oxidases. 

 Alcoholic solutions of guaiacum develop peroxid very rapidly. Only large 

 pieces of gum with little surface exposure should be used. Saturated alcoholic 

 solutions of the gum seemed to change less rapidly. Tannin interferes with 

 both direct and indirect oxidase (peroxidase) action, this effect being prevented 

 by precipitating tannin with hide powder. Certain fruits, as Carica papaya, 

 give an oxidase test only after ripening. The juice of certain green fruits 

 when treated with hide powder then gave the oxidase test. Standard color 

 solution of indigo carmin was used to make comparative determinations of 

 amounts of oxidases in various parts of the tea plant as judged by the depth 

 of the blue color due to the oxidation of guaiacum." " Direct oxidase is not 

 an enzym in the strict sense of the term but is an organic peroxid as held by 

 Bach and Chodat. The peroxidase from tea leaves is very resistent to heat 

 and is not subsequently regenerated when allowed to stand. Mercuric chlorid, 

 hydrocyanic acid, and solutions of mineral acids destroy the oxidizing action 

 of tea leaves. Exposure to light seems to prevent formation of peroxid but has 

 no effect upon the peroxidase preparation. Yeasts present in tea fermentation 

 do not secrete any extracellular oxidases which are involved in the production 

 (if common tea." 



In regard to the von Lorenz method for the determination of phosphorus, 

 H. Xeubauer and F. Lucker iZtschr. Anahjt. Chem., 51 (1912), No. 3-4, pp. 

 161-175). — By substituting acetone for alcohol and ether for washing the molyb- 

 date precipitate the cost of conducting this test can be much reduced. 



The precipitate, which is obtained in the usual way, is collected in a Gooch 

 crucible containing filter paper or on the Neubauer platinum sponge crucible, 

 washed 4 times with a 2 per cent solution of ammonium nitrate and 3 times 

 with acetone, and then placed in a vacuum desiccator at a pressure not greater 

 than 150 mm. of mercury for * hour and weighed. If the weighing can not be 

 done immediately, the crucible is placed in an ordinary desiccator over sulphuric 

 acid until the weighing time. The results obtained compared well with those 

 obtained by the usual method. The spent acetone may be recovered by dehydra- 

 tion with potassium carbonate. 



Estimation of nitrites in potable waters, G. D. Elsdon (Chem. Neivs, 105 

 (1912), No. 2739, p. 2Ji3). — " For the following reasons the author much prefers 

 the Griess-Ilosvay reagent for testing for nitrites, both qualitatively and quanti- 

 tatively : (1) The color is practically steady after standing about 2 hours, 

 and it is easy to compare and match. (2) It is not affected by ferrous and ferric 

 salts. (3) Only one solution has to be added, and this will keep for months 

 without decomposition. 



" The stai'ch-iodid test only seems to have one good point, namely, that the 

 solutions required are ordinary laboratory reagents." 



Determination of calcium in the presence of magnesium, E. C. Carron 

 (Ann. Chim. Analyt., 17 (1912), No. J/, pp. 127-129; abs. in Jour. 8o<^. Chem. 

 Indus., 31 (1912), No. 9, p. ^60). — Much difficulty is experienced in the separa- 

 tion of calcium from magnesium by the usual methods, particularly where a 

 large excess of magnesium is present. The following method is recommended 

 as being an accurate one for this purpose: 



" The solution of the chlorlds — which may contain ammonium chlorid and 

 ammonia — is concentrated to 60 or SO cc. and made slightly alkaline. After 

 the addition of 20 cc. of ammonium bisulphite solution — prepared by saturating 



