Chemistry and Physics. 499 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Melting-point of Spodumene. — Endell and Rieke have 

 made some new observations upon this subject and have drawn 

 interesting geological conclusions from their results. They used 

 spodumene from Branchville, which appears to be much purer 

 than the material from Stirling which has been used by Doelter 

 for melting-point determinations. The authors find that the min- 

 eral, when heated for an hour or more to about 950° C, changes 

 its specific gravity from 3*147 to about 2-37, a gain in volume of 

 24 per cent. At the same time, between 920° and 980° C, the 

 monoclinic substance loses its double refraction and acquires a 

 lower average index of refraction ; and the heating-curve shows 

 a change at nearly the same temperature. It was found that the 

 material must be finely powdered to show these changes accu- 

 rately. The authors consider 950° C. as the true "melting-point" 

 of spodumene, although it is perfectly hard and solid at this tem- 

 perature and it does" not actually fuse until a temperature of about 

 1380° C. is reached. They do not admit the existence of a solid, 

 isotropic modification of the mineral, because there is no differ- 

 ence between the specific gravity and index of refraction of the 

 unf used solid and the glass. 



Since spodumene occurs at Branchville, Conn., in a pegmatite 

 vein, the authors suggest that it may serve as a measure of geo- 

 logical temperature, as they believe that it could not be formed 

 above about 950° C. They consider the effect of pressure as prac- 

 tically of little importance, since from Clapeyron's formula they 

 calculate the effect as only 7° C. per kilometer in depth. — Zeitschr. 

 anorgan. Chem., lxxiv, 33. h. l. w. 



2. The Detection of Nitric Acid in the Presence of Nitrous 

 Acid. — Sen and Dey have found that hydrazine reacts with 

 nitrous acid according to the following equations : 



N 2 H 4 + 2HN0 2 = N 2 + N 2 + 3H 2 

 N 3 H 4 + HN0 2 = NH 3 + N 2 + H 2 



They have, therefore, used hydrazine sulphate for the purpose of 

 removing nitrites, in order that nitrates, upon which the reagent 

 has no action, may be detected. The method appears to be much 

 more accurate than that of Piccini, which depends upon the remo- 

 val of nitrous acid by means of urea in the presence of dilute sul- 

 phuric acid, because this reaction is not rapid enough to prevent 

 the formation of traces of nitric acid from the spontaneous decom- 

 position of the free nitrous acid. The hydrazine method has the 

 advantage that the nitrous acid does not need to be set free by 

 another acid, since the sulphuric acid combined with the hydra- 

 sine furnishes sufficient acid for the decomposition of the nitrite, 

 and moreover the reaction goes so rapidly that no nitric acid can 



