AGRICULTURAL CHEMISTRY AGROTECHNY. 413 



Titration of small quantities of carbon dioxid, A. Dobneb {Hnppe-Seyler''s 



Ztschr. Physiol. Chcm., 88 {WIS), No. 6, pp. 425-429, fig. 1; ahs. in Jour. Chem. 



Soc. [London], 106 (1914), No. 611, II, p. 218).— In tliis method, heating of the 



barium hydroxid is dispensed with because it leads in glass vessels to an 



appreciable change of titer. In the modified process good results are obtained 



N 

 by absorbing the carbon dioxid with ^ barium hydroxid in the cold using a 



special form of apparatus which is shown. 



A comparison of methods for the determination of oxygen in waters in 

 presence of nitrite, E. Elvove (Pub. Health Scrv. U. S., Ili/g. Lah. Bui. 96 

 (1914), pp. 15-35). — "In comparison with the Winkler method, the Levy 

 method " is decidedly disadvantageous. Regarding the Winkler method as modi- 

 fied by Hale and Melia (E. S. R., 31, p. 411), it is pointed out that their warn- 

 ing ' that solutions acidified ready for titration should not stand in contact with 

 air for several hours before titrating ' may be misleading, since low results were 

 obtained even when the solutions were kept in closed bottles which had been 

 completely filled with these solutions. Furthermore, even a period of only one 

 hour was sufficient to cause low results. In the presence of considerable nitrite 

 the results may also be too high if there is not a sufficiently long period inter- 

 vening between the addition of the potassium acetate and the titration of the 

 iodin. 



"In order to obtain accurate results by the acetate modification of the 

 Winkler method, the titration should therefore be carried out immediately 

 after a certain interval has elapsed since the mixing with the potassium acetate. 

 Under the present conditions (5 parts per million of nitrite and temperature 

 about 20°C.), an interval of 15 minutes was found to be the proi>er time to allow 

 for the potassium acetate to remain in contact with the iodin before the latter 

 is titrated. 



" Hale and Melia's apparent explanation of the counteracting effect of the 

 acetate on the nitrite interfei'ence on the assumption that its function is ' to 

 neutralize the hydrochloric acid and render the solution acid with acetic acid ' 

 does not seem to be a sufficiently complete explanation, since an acetic acid 

 medium was found not to prevent these interferences. The power of potassium 

 acetate to counteract the nitrite interference is probably due to its further de- 

 pression of the dissociation of the acid ; an excess of the acetate is therefore 

 essential. 



" The permanganate modification of the Winkler method, since it is applica- 

 ble in the presence of nitrite and organic matter, is preferable to the acetate 

 modification which counteracts only the interference from nitrite. In carrying 

 out the permanganate modification in bottles of about 270 cc. capacity, each 

 bottle should contain not less than 0.45 gm. potassium iodid and the amount of 

 excess of potassium oxalate should not be more than 1 cc. of the 1 per cent 

 solution." 



A study of the methods for extractions by means of immiscible solvents 

 from the point of view of the distribution coefficients, I, J. W. Mabden 

 (Jour. Indus, and Engin. Chem., 6 (1914), ^o. 4, pp. 315-320). — "A practical 

 application of the distribution ratio has been made in a study of a few of the 

 extraction methods given in the bulletins of the U. S. Bureau of Chemistry 

 with the view of pointing out the fact that definite directions are needed in 

 our extraction methods which give a definite amount of the material in ques- 

 tion. A modification of the method of analysis for acetanilid in hydrogen 

 peroxid has been suggested. The method for acetanilid, vanillin, and coumarin 



"Arch. Hyg., 32 (1897), p. 305. 



