478 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. Tlie Colorimetric Determination of Manganese 'by Oxida- 

 tion with Periodate. — The rapid determination of small quanti- 

 ties of manganese by converting it into the form of permanganate 

 and comparing the color with a solution of a known amount of 

 the latter was suggested as long ago as 1845 by Crum, and later 

 this principle has been very extensively employed in practical 

 analysis, especially in the examination of iron ores and steels. 

 Several oxidizing agents have been employed for this purpose, 

 lead dioxide, an alkali persulphate in presence of silver nitrate, 

 and sodium bismuthate, all of which are applied in nitric acid 

 solution. H. H. Willard and L. H. Greathouse have now 

 found a new reagent, periodic acid or its salts, for this purpose 

 and they believe it to be free from all the faults of the previous 

 methods. The periodate is reduced to iodate according to the 

 following equation : 



2Mn(N03)2 + 5HI0, + SH^O = 2HMnO, + 5HIO3 + 4IINO3 



Only a small excess of periodate is required, but the success 

 of the reaction depends upon a sufficient concentration of the 

 acid, for otherwise a precipitation occurs, either of manganese 

 dioxide, or of manganic periodate. 



The author recommends that the material to be analyzed be 

 brought into a solution containing in 100 cc at least 10 to 15 cc 

 of concentrated sulphuric acid, 20 cc of nitric acid or 5 to 10 cc 

 of syrupy phosphoric acid, or mixtures of two or more of these 

 acids. The solution should have been previously freed from 

 reducing agents by boiling with nitric acid, with the addition 

 of a persulphate if carbon compounds are present, as in the case 

 of steel. Ammonium salts do not interfere, but it is best to 

 remove any hydrochloric acid by evaporating with sulphuric 

 acid, although small quantities may be removed by boiling after 

 adding the periodate. The final reaction is obtained by adding 

 0.2 to 0.4 g of potassium periodate or of sodium periodate, or 

 an equivalent amount of sodium metaperiodate, boiling for a 

 minute, keeping hot for 5 to 10 minutes and finally cooling. 

 The solution is then diluted to the proper volume and compared 

 in a colorimeter with a standard of known manganese contents, 

 similarly prepared. The solutions used for comparison should 

 not contain more than 1 mg of manganese in 50 cc, for other- 

 wise the color will be too strong. — Jour. Am. Chem. Soc., xxxix, 

 2366. H. L. w. 



2. The Preparation of Cyanamide from Calcium Cyanam- 

 ide. — E. A. Werner calls attention to the unsatisfactory , yields 

 of cyanamide, CNNII2, by the methods heretofore used for the 



