68 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistky and Physics. 



1. On the Study of Chemical Reactions by means of the Re- 

 fractive Index. — It has been shown by Fery that the occurrence 

 of chemical changes in solution may be detected and studied, by 

 comparing the refractive indices of solutions containing two sub- 

 stances which are capable of acting one on the other, with those 

 calculated on the assumption that the observed index is the mean 

 of the indices of the two constituents. In a solution containing 

 sodium hydroxide and nitric acid for example it was observed 

 that the maximum deviation of the experimental from the calcu- 

 lated values occurred in a solution containing 8 parts of NaOH 

 and 12*31 parts of HN0 3 in 100 of water, the ratio 12*31/8*00 

 being nearly equal to that of HN0 3 /NaOH. When alkalies are 

 mixed with sulphuric acid, there are two points at which changes 

 of the refractive index occur in the curve, one corresponding with 

 a mixture that would form an acid salt, the other to one that 

 would form the normal salt. In the case of phosphoric acid the 

 curve has three such points. In cases where no chemical action 

 occurs, the observed and calculated values for the indices of re- 

 fraction are found to coincide, the curve for the refractive indices 

 of such mixtures being a continuous straight line. Moreover, the 

 author has observed certain other slight breaks and changes in 

 the refractive-index curve, which he attributes to the formation 

 of special hydrates by the union of water with the substances 

 under examination. In the case of sulphuric acid, a special study 

 showed that such breaks occurred with solutions corresponding 

 to hydrates of H 2 S0 4 with one, one and a half, two and four 

 molecules of water respectively. — C. R., cxv, 1309 ; J. Chem. Soc, 

 lxiv, ii, 201, May, 1893. g. f. b. 



2. On the Preparation of Chlorine by means of Nitric Acid 

 and Manganese dioxide. — Several years ago Schlosing proposed 

 a process for preparing chlorine by acting on hydrochloric acid 

 with manganese dioxide and nitric acid ; the reaction taking 

 place according to the equation : 



MnO, + (HC1), + (HN0 3 ) = Mn (N0 3 ) 2 + (H a O) a + CI, 



and evolving theoretically the whole of the chlorine contained in 

 the hydrogen chloride. In practice, using the dioxide and the 

 hydrochloric acid (sp. gr. 1*184) in the proportion given in the 

 equation, and nitric acid (sp. gr. 1*4245) in excess to the extent of 

 75 per cent, a yield of 98-99 per cent of the calculated quantity 

 of chlorine is obtained. To the acid mixture one-seventh of its 

 volume of water is added and the whole is heated to 135°. 

 Lunge and Peet have studied this reaction more completely. 

 They find that the resulting manganese nitrate may be entirely 

 converted, by heating, into manganese dioxide and the lower 





