1892.] Mineralogy and Petrography. 517 



accompany the corundum. These experiments throw some light upon 

 the production of corundum in metamorphosed limestones. Under 

 similar conditions magnesia yields brncite. When calcium silicate is 

 treated with sodium borate at high temperatures under pressure dath- 

 olite crystals are formed, according to Wyrouboff. 1 



Miscellaneous. — A new contribution to the discussion of the cause 

 of optical anomalies is from the pen of Karnojitzky 2 , who ascribes the 

 phenomena to polymerisni. Paramorphic substances are thought 

 to be polymeric, with the higher polymer more stable than the simpler 

 one. The latter usually possesses a higher degree of symmetry than 

 the former, and hence, when it forms first it gives a higher degree of 

 symmetry to its crystals than is possessed by those of its paramorph — 

 the more stable, more complicated compound. The author develops 

 this idea in a very logical and clear manner, and instances many 

 examples to indicate the probability of the correctness of his state- 



Retgers 3 proposes to test the isomorphism of different substances by 

 forming of them mixed crystals, which, if the two substances used be 

 isomorphous, will differ continuously in their physical properties. In 

 the case of colored salts the test most easily applicable is that of color. 

 If potassium chlorate and the corresponding permanganate be dissolved 

 in water and a drop of each be placed in an object glass and allowed 

 to come in contact, the crystals termed at the junction of the two 

 drops will be intermediate in color between those formed at a distance 

 from it. In the case of salts that are not isomorphous no gradation in 

 color will be observed. In his article the author mentions the many 

 compounds that he has discovered to be isomorphous. 



Lemberg* suggests a modification of micro-chemical analysis by 

 which minerals are detected rather than their constituent elements. 

 For instance, instead of distinguishing between hauyne and sodaliteby 

 studying their elements, the author would study the effect of the min- 

 erals themselves upon reagents, e. g. sodalite will precipitate silver 

 chloride from a weak nitric acid solution of silver nitrate, whereas 

 hauyne will not do so. Chabazite reacts rapidly with ammonium 

 chloride and generates ammonia, while thomsonite, analcite and leucite 



