1892.] Mineralogy and Petrography. 59 



double refraction was negative and pleochroism strong. 2 V=82°, and 

 composition : 



Si0 2 A1 2 3 Fe,0 3 FeO MgO CaO Na,0 K 2 Loss 

 42.35 8.11 7.91 10.11 14.33 13.21 2.18 1.87 .91 

 —Otto and Kloos 1 find perfect crystals of periclase on a nnifTel in 

 which magnesium oxychloride has been heated. 



General. — The solubility of quite a number of minerals in pure water 

 and in dilute salts has been carefully investigated by Doelteiv The sul- 

 phides, sulpho-salts, oxides and silicates examined are slightly soluble in 

 wuter, with the addition of sodium sulphide the solubility of the first 

 two groups is increased while that of the oxides is increased by sodium 

 fluoride. The' carbonate of sodium appears to produce but little effect 

 upon these. The silicates are more readily soluble in carbonated water 

 and in dilute solutions of sodium carbonate. Distilled water seems to 

 act simply as a solvent upon all classes, whereas the other reagents 

 produce more or less decomposition. Gold is dissolved to some extent 

 in both the silicate and the carbonate of sodium at high temperatures. 

 — Two instruments for the observation of the optical properties of min- 

 erals at high temperatures are described by Klein, and a third by 

 Fuess. 4 One is adapted for use on the microscope, where temperatures 

 not greater than 450° are required. The second allows of observations 

 at a bright red heat, the source of heat being electrical. The third is 

 for use with gas. — Miers 5 gives a description of a simple and cheap, 

 though quite accurate goniometer for student's use. Rinne' outlines an 

 easy method of determining the character of the double refraction in 

 uniaxial and biaxial crystals in converged light, based on the use of the 

 gypsum plate. Practically the determination depends largely upon 

 the colors of different segments of the microscopic field. It is espec- 

 ially valuable in determining the sign of weakly doubly refracting 

 substances. — The fifth part of Hintz's Handbuch der Mineralogie 7 

 concludes the treatment of the mica group, and deals in the usual 

 thorough manner with the chlorite and serpentine groups. 



'Ber. d. Deutsch. Chem. Gesell, 1891, p. 1488- 



2 Min. u. Petrog. Mitth. XI, 1890, p. 319. 



:; Xeues. Jahrb. f. Min., etc., 1890, I, p. 65. 



+ Ib. B. B., VII, p. 406. 



*Min. Magazine, IX, 43, p. 214- 



6 Neues. Jahrb. f. Min., etc., 1891, I, p. 21. 



7 Lei P zig 1891, p. 641-800. 



