M. Gaudin on the Preparation of Artificial Sapphires, 109 



to mc probable, that the difference between the values of the 

 potential function on both sides of the partition remaining the 

 same, the quantity of electricity passing through the parti- 

 tion in the unit of time will be somewhat smaller when the 

 translation of the liquid is obstructed by a hydrostatic counter- 

 pressure, than when this is not the case; in other words, the 

 translation of the liquid being more obstructed, the partition 

 offers a greater resistance to conduction. For the reasons above 

 stated, however, the difference can be but small in liquids which 

 do not conduct very badly. 

 Zurich, April 25, 1857. 



XV. Chemical Notices from Foreign Journals. 



By E. Atkinson, Ph.D. 



[Continued from vol. xiv. p. 278.] 



FOR the preparation of colourless crystals of alumina, or arti- 

 ficial sapphires, Gaudin* gives the following process: — 

 A mixture of equal parts of alum and sulphate of potash, which 

 have been previously ignited and powdered, is introduced into a 

 crucible lined with lampblack, and the crucible is then heated 

 for a quarter of an hour in a blast-furnace. When the crucible 

 is cold, a mass full of brilliant points is found in the cavity of the 

 charcoal. It consists of sulphide of potassium enclosing crystals 

 of alumina, which are large in proportion to the size of mass 

 operated on. The crystals are obtained in the form of fine sand 

 by treating the mass with dilute aqua regia, and subsequent 

 washing with water. The crystals are harder than native rubies, 

 quite transparent and colourless, for coloured metallic oxides are 

 reduced by the carbon. Gaudin ascribes the formation of these 

 crystals to the fact that sulphide of potassium is formed, which 

 acts as a solvent for alumina at a high temperature, and on cool- 

 ing alumina crystallizes out. He obtained the crystals also by 

 heating together calcined alumina and sulphide of potassium in 

 a luted crucible. 



In the course of some experiments on titanium, made with a 

 view of investigating its properties in the comi)act form, Woliler 

 and Dcvillet have found that a great affinity exists between that 

 mctdl and nitrogen ; — that titanium, at least at the moment of 

 its formation, can unite directly with the nitrogen of the atmo- 

 sphere. Nothing is more difficult than the preparation of pure 

 metallic titanium. It can only be obtained so with certainty by 



* Comptes Reiidus, April (>, 1S.'')7. 

 t Licbig's Anualen, August 1857. 



