Chemistry and Physics. 61 



carbon crucible for three minutes by means of an arc of 900 

 amperes and 45 volts. A crystalline mass is formed containing 

 cavities lined with crystals. The crystals of spinel thus formed 

 are colorless, octahedral, scratch quartz, have a specific gravity 

 of 3*57 at 15°, and have a composition corresponding to the 

 spinel formula MgAl 2 4 . It is easy to obtain colored spinels in 

 this way by additions of small quantities of oxides of nickel, 

 iron, chromium, cobalt, etc. Attempts were made to prepare 

 more basic magnesium aluminates by fusing alumina with several 

 molecular proportions of magnesia, but spinel w r as invariably 

 formed, crystallized in the excess of fused magnesia. — Bull. Soc. 

 Ghim., xxv, 670. h. l. w. 



5. The Size of the Sulphur 3Iolecule. — Biltz and Preuner 

 have made an elaborate series of determinations of the specific 

 gravity of sulphur vapor under diminished pressures which 

 varied from 14 to 539 mm and at the temperature of sulphur 

 boiling at atmospheric pressure, or between 447 and 450°. At 

 the lowest pressures used the specific gravities corresponded to 

 molecules a little heavier than S 4 , and as the pressure increased 

 the specific gravities rose rapidly to values corresponding to S 5 , 

 S 6 and S T , and then increased very slowly. The results when 

 plotted indicate a curve beginning at S 2 at mm and approaching 

 S s at high pressures. The authors conclude that sulphur vapor 

 consists wholly of S 8 and S 2 molecules, and that there is no 

 evidence of the existence of the previously assumed S 6 aggrega- 

 tions. — Monatsh. f. Chem., xxii, 627. h. l. w. 



6. A Direct Gravimetric Method for the Pstimatio?i of 

 Boric Acid. — It has been found by Partheil and Rose that it 

 is possible to extract boric acid, from an aqueous solution 

 acidified with hydrochloric acid, by means of ether. The 

 extraction apparatus used is one which acts continuously, the 

 ether being distilled and condensed in such a manner that it flows 

 up through a spiral tube containing the liquid to be extracted 

 and then overflows into the distilling-flask. An extraction last- 

 ing 18 hours was found desirable, and the ether finally remaining 

 in the flask was removed in a vacuum desiccator over sulphuric 

 acid in order to weigh the boric acid as H 3 B0 3 . Two test 

 analyses on boric acid and borax gave very accurate results, 

 and the authors state that they have applied the method to the 

 analysis of many minerals. For the application of the process, 

 the boric acid solution should contain neither sulphuric, phos- 

 phoric nor nitric acids, nor any considerable amount of iron. The 

 presence of zinc and arsenious acid would also interfere with the 

 operation. — Berichte, xxxiv, 3611. h. l. w. 



7. The Pressure of Light. — Two papers have recently appeared 

 on this subject : E. L. Nichols and G. F. Hull in the Physical 

 Review, November, 1901, and P. Lebedew in the Ann. der 

 Physik, No. 11, 1901. The investigators employ similar appa- 

 ratus — vanes of varying material, suspended in a vacuum. They 

 distinguish carefully the radiometer effects from the pressure of 



