19J0J AGRICULTURAL CHEMISTRY — AGROTECHNY. 803 



10 cc. of n/10 sodium hydroxid to stop the diastatic action, and diluted with 

 •water to the 2(X) cc. mark. 



" Twenty-five cc. of tliis .solution i.s transferred to a 300 cc. Erlenraeyer flask, 

 exactly 10 cc. each of Fehling's solutions I and II added, and the volume 

 broufrht up to 50 cc. with 5 cc. water. The mixture is boiled slowly for 2 minutes 

 and immediately cooled under the cold water faucet, but not nmch under 25°. 

 Ten cc. of a 30 per cent potassium iodid solution, or 3 gm. potassium iodid and 

 10 cc. of a 25 per cent sulphuric acid solution, are added successively and the 

 liberated iodin titrated with a n/10 thiosulphate solution to a creamy yellow 

 color, the solul)le starch present serving as an indicator." 



The diastatic capacity in degrees Lintner is obtained by dividing the amount 

 of thiosuliiliate equivalent to the copper sulphate reduced by the sugar by the 

 amount of thiosulphate u.sed in a blank test (25 cc, 5 cc. water, 20 cc. Feh- 

 ling's solution) and multiplying the result by the factor 320. 



A simple method for titrating electrometrically to a desired end point in 

 acid-alkaline reactions, P. E. Klopstkg {Science, n. ser., 52 {1920), No. 1331, 

 pp. 18, 19). — The author suggests the utilization of the hydrogen electrode as 

 a means of titrating a solution of unknown pH value to a definite H-ion con- 

 centration. The technique is essentially as follows : 



A solution having a pH value corresponding to the desired end point of the 

 titration, selectetl from the standard formulas of Clark and Lubs (E. S. R., 37, 

 p. 506), is placed in one vessel with a hydrogen electrode. This is connected 

 by a salt bridge of saturated potassium chlorid with the cell containing another 

 hydrogen electrode in the unknown solution. The two electrodes are connected 

 by means of a tapping key and a galvanometer of high resistance. The titrating 

 solution is then added to the unknown until the galvanometer shows no deflec- 

 tion upon tapping the key, thus indicating that the H-ion concentrations of the 

 two cells are equal. 



It is pointed out that such a titration can be carried out regardless of the 

 color or turbidity of the solution, and that its accuracy is limited only by the 

 accuracy with which the pH value of the standard solution is known. 



Simplification of the reaction of manganese salts of Caron and Raquet, 

 G. DENiGfes {Ann. Chim. Analyt., 2. ser., 2 {1920), No. 7, pp. 215, 216).— A simplifi- 

 cation of the reaction of manganese salts noted by Caron and Raquet (E. S. li., 

 41, p. 504) is described in which the active oxidizing agent is replaced by 

 atmospheric oxj-gen in an alkaline medium, and pota.ssium oxalate by free oxalic 

 acid, thus obviating the necessity of using acetic acid. 



The technique of the modified method consists in adding to 5 cc. of the solu- 

 tion of the manganese salt one or two drops of sodium hydroxid, shaking 

 the mixture in the presence of air until a brown color appear-s, and then 

 adding drop by drop with constant shaking a cold solution of oxalic acid until 

 the brown color distippears and the cliaracteristic red color of the alkaline 

 manganic oxalate appears. 



The determination of potassium and its separation with sodium as so- 

 dium potassium cobaltic nitrite, P. Wknger and C. HiiMKx {Ann. Chim. 

 Analyt., 2. ser., 2 {1920), No. 7, pp. 198, i99).— Experimental data are reported 

 verifying the formula NaK:Co(NOj)o for .sodium potassium cobaltic nitrite by 

 determining both the cobalt and the potassium in the precipitated salt. The 

 authors recommend as a rapid method of determining potassium its precipita- 

 tion with sodium cobaltic nitrite, the determination of cobalt either gravimetri- 

 cally or volumetrically, and the use of the theoretical coefficients 2.5254 for 



2KC1 KiO 



Q or 1.5932 for qT" for calculating KCl or K2O from tlie ascertained weight 



of cobalt. 



k 



