AGRICULTUBAL CHEMISTRY AGROTECHNY. 211 



advantage lies in the fact that a large number of these tubes can be collected 

 and the copper determinations made at one time. It has also been successfully 

 applied to the estimation of copper in Paris green and arsenite of copper. It 

 is conducted as follows : 



"The copper is dissolved in 5 cc. of concentrated nitric acid [the filter], 

 thoroughly washed with hot water, and the filtrate run into an Erlenmeyer 

 Ilask by means of suction. The solution is evaporated to small volume to expel 

 excess of acid, and afterwards diluted with 60 cc. of water. Too great con- 

 centration should be avoided, as it often results in the precipitation of a very 

 insoluble form of copper and the loss of the determination. Twenty-five cc. 

 of a saturated solution of zinc acetate and 20 cc. of potassium iodid (165 gm. 

 to 1,000 cc.) are added, and the free iodiu titrated with tenth-normal sodium 

 thiosulphate solution (24.83 gm. per liter). The thiosulphate is run in grad- 

 ually, with constant shaking, until the brownish yellow color (iodin) has been 

 largely destroyed; then 2 cc. of starch paste (1 gm. to 200 cc.) are added and 

 the titration continued until the blue particles have entirely disappeared. To- 

 ward the end of the reaction the flask should be stoppered and shaken thor- 

 oughly. 



" The copper equivalent of the thiosulphate is determined by diluting 25 cc. 

 of a standard copper solution with water, evaporating and titrating exactly as 

 in the test. The standard solution is prepared by dissolving 10 gm. of pure 

 dry metallic copper in 200 cc. of concentrated nitric acid, and making up to a 

 liter with water at 20° C. The solution should be analyzed gravimetrically, 

 and will keep almost indefinitely. From this data the reducing action of the 

 sugar solution can be readily calculated in terms of copper, and by conversion 

 tables the corx*esponding amount of sugar." 



A new volumetric method for the determination of mang'anese, F. J. Metz- 

 GEB and R. F, McCrackan (Jour. Atner. Chem. Soc, 32 (.1910), Xo. 10, pp. 1250, 

 1251). — The solutions used are a tenth-normal potassium permanganate solu- 

 tion, a solution of ferrous sulphate of about equivalent strength, and a solution 

 of manganous sulphate carefully standardized gravimetrically by weighing as 

 pyrophosphate. The method is as follows : 



" Place 50 cc. of the standard manganese solution in a 300 cc. Erlenmeyer 

 flask, add 10 to 15 cc. of concentrated sulphuric acid, and allow to cool. Add 1 

 to 2 gm. of finely powdered sodium bismuthate in such a way that none of 

 the powder sticks to the sides of the flask. Place the flask in a beaker of water 

 so that the level of the solution is several inches below the level of the water 

 in the beaker. Heat slowly to boiling and boil till the precipitate of basic 

 bismuth compound settles well and has a granular appearance (about 20 min- 

 utes* boiling is usually necessary). Remove the flask and cool under running 

 water, add a known excess of ferrous sulphate solution, dilute to about 200 cc, 

 and titrate back with standard permanganate solution. 



" The manganese standard of the permanganate is calculated from the reac- 

 tion which may be represented thus: Mn++++ + 2Fe++ —> i\ln++ + 2Fe+++. Or 

 the value of the permanganate in terms of iron multiplied by 0.4918 gives the 

 value in terms of manganese." 



The detection of small amounts of manganese in foods, Dumitbescou 

 and Mlle E. Nicolau (Ann. Falsif., 3 {1910), No. 23, pp. 370-372) .—The 

 method consists of oxidizing the manganese (if present in the ash) with a 

 40 per cent solution of ammonium persulphate, adding a drop of 2 per cent 

 cobalti-nitrate to the solution, and boiling, when the characteristic permanga- 

 nate color will be obtained. 



Judging the quality of wheaten and rye fl.our, O. Rammstedt {Ztschr. 

 Offentl. Chem., 16 {1910), No. 12, pp. 231-243).— A critical discussion of the 



