428 Scientific Intelligence. 



as a yellow precipitate. This under the microscope is seen to 

 consist of stellate crystals with triangular arms, generally six, 

 arranged in rectangular planes along the axes of a cube, and 

 which polarize light. The author regards this as the most sen- 

 sitive and distinctive test for arsenic. He prepares the ammonium 

 molybdate solution by dissolving ten grams of this salt and 25 

 grams of ammonium nitrate in 100 c. c. of warm water. After 

 cooling, 100 c. c. of pure nitric acid of sp. gr. 1 # 20 are added drop 

 by drop with active stirring. Then the liquid is heated on the 

 water bath for ten minutes, allowed to cool and after 48 hours, 

 filtered. — C. B., cxi, 824; J. Chem. Soc. 9 \x, 364, March, 1891. 



G. F. B. 



6. On Priestley's JEJudiometric method. — The method adopted 

 by Priestley for measuring the oxygen in the air by mixing a 

 measured volume of nitrogen dioxide with it and noting the 

 diminution of volume, has been condemned as inaccurate. Wank- 

 lyn has investigated the matter and concludes that the inaccuracy 

 is due to the oxygen present in the water through which the gas 

 is made to pass. This source of inaccuracy may be avoided by 

 using a Hempel apparatus and measuring the air in the gas 

 burette and then passing it into an absorption pipette contain- 

 ing water. The nitrogen dioxide is introduced into the gas 

 burette and measured and then (without bubbling through water) 

 passed into the air in the absorption pipette. After the nitric 

 tetroxide formed has been absorbed by the water in the absorp- 

 tion pipette the gas is passed back into the gas pipette and is 

 again measured. — J. Chem. JSoc, lx, 362, March, 1891. g. f. b. 



7. On Crystalline Liquids. — Attention has been drawn by 

 Lehmanx to the fact that the optical behavior of certain liquids is 

 such as to suggest a crystalline structure in them. Chemically 

 however these liquids are homogeneous and their anisotropic 

 character is not due to external stress. He now raises the ques- 

 tion whether liquids which are isotropic are non-crystalline, or 

 whether they are crystalline and isometric. In view of the free 

 miscibility of liquids, however, he concludes that they are non- 

 crystalline, since were this not the case they could mix only with 

 isomorphous substances. This conclusion the author supports 

 by experiments on the miscibility of crystalline liquids with each 

 other and with solid crystals. Liquid crystals, when heated 

 between cover glasses to a point slightly above that at which 

 they pass into ordinary liquids, retain on cooling the original 

 direction of their optic axes owing probably to condensation and 

 consequent higher melting point of a layer on the surface of the 

 glass. Isomorphous liquid crystals exhibit the phenomena of 

 diffusion and hence the capability of solids to form mixed crystals 

 appears to correspond exactly with the process of mixing or dif- 

 fusion in liquids. — Ann. Phys. Chem., xli, 525. — J. Chem. Soc, 

 lx, 249, March, 1891. 



8. On the Refractive indices of Water. — Bruhl has measured 

 the refractive indices of water for light of certain wave-lengths 



