704 PETROLOGICAL ABSTRACTS AND REVIEWS 



localities. The phenocrysts are usually albite, in two occurrences orthoclase 

 with intergrown albite; the groundmass is trachytic albite with small amounts 

 of magnetite, chlorite, and a little sericite. 



ScHNEiDERHOHN, H. " Die Methodeii zur mikroskopischen Unter- 

 suchung kristallisierter Korper," Handhuch der mikroskopischen 

 Techmk, Stuttgart, X (1914), 45-94, figs. 68. 



Gives a brief but very good summary of petrographic-microscopic methods, 

 well illustrated by figures. Attention is called to the fact that these methods 

 are applicable not only to the determination of rocks, but that they may be 

 used in the determination of natural and artificial salts, synthetic minerals, 

 cement, etc. 



ScHNEiDERHOHN, Hans. " Uber Methodcii, um rasch und cinfach 

 aus Photographien Strichzeichnungen herzustellen," Sencken- 

 bergiana, I (191 9), 190-93, figs. 2. 



While this is not a petrographic article, the method here given for rapidly 

 reproducing photographs may be of interest to petrographers, especially in 

 these days of poor print-paper. A developing-paper print of the thin section 

 or other petrographic subject is "inked-in" with waterproof ink. It is then 

 immersed in subdued light for a few minutes in acid hypo, and then, without 

 washing, placed in a rather concentrated solution of about equal parts copper 

 sulphate and potassium bromide. In a few minutes the silver image will 

 become altered to a yellowish image of silver bromide. When of a yellow color, 

 it is washed for a few moments and re-immersed in the hypo until the yellow 

 color disappears and leaves a white background. Without first immersing in 

 hypo the operation is somewhat slower. Instead of copper sulphate, potassium 

 ferricyanide may be used. A second method, less desirable on account of the 

 poisonous nature of the material, but more rapid, is to dissolve the sUver in a 

 dilute solution of potassium cyanide. The print should be thoroughly washed 

 afterward. 



ScHNEiDERHOHN, Hans. "Die mikroskopische Untcrsuchung uii- 

 durchsichtiger Mineralien und Erze im auffallenden Licht und 

 ihre Bedeutung fiir Mineralogie und Lagerstattenkunde, " 

 Neues Jahrb., B. B. XLIII (1920), 400-438. 



Here is a most excellent summary of work done on the determination of 

 opaque minerals by means of incident Hght under the microscope. A long 

 bibliography is given. 



