578 Journal of Applied Microscopy. 



figures ; also that with the mineral apatite, the deeper, darker etch figures some- 

 times enclose smaller figures of the other type. 



The conclusion appears to be that etch figures of unexpectedly low grade of 

 symmetry, while undoubtedly due to structural peculiarities, are not to be hastily 

 interpreted, and are not thoroughly understood phenomena analagous to optical 

 anomalies. a. j. m. 



V !/,„ ♦ L' ui 1/ «; ui I T^- The view at one time held, that colors 

 V. Kraatz=Koschlau, K. u. Wohler, L. Die ' 



naturlichen Fiirbungen der Mineralien. uniformly distributed but not properly 



Tschermak's Min. u. Petr. Mitt. 18: 304, belonging to a substance, were due to 



a mechanical inclusion of foreign col- 

 oring substance, so finely divided as to be beyond the range of our microscopes, 

 has been abandoned for the theory of isomorphic replacement and a large series 

 of colored solid solutions (feste Losungen of Van't Hoff) have been artificially 

 made. 



The nature of the coloring material has been assumed by most to be usually 

 organic, and in a few known instances inorganic. Weinschenk has lately, how- 

 ever, on the basis of an examination of smoky quartz, theorized that the coloring 

 substances are in general inorganic, ascribing the color of smoky quartz, smoky 

 topaz, and octahedrite to a sesquioxide of titanum, that of zircon to a sesquioxide 

 of zirconium. 



The authors have tested qualitatively and quantitatively a number of minerals 

 from many localities, and find no support for the theory of Weinschenk^ but on 

 the contrar)'^ find that with a number of minerals, when heated in presence of 

 oxygen, they obtained the smell of charred organic matter, phosphoresence and 

 evolution of CO., wJtile the color lasted, but on the decolorized matter these tests 

 were negative. According to their results, the following classification results : 

 1st. Coloring Alaterial Entirely Organic. — Fluorite, apatite, barite, celestite, 

 anhydrite, calcite, halite, smoky topaz, zircon, microcline, rubellite, topaz. 



2(1. Coloring Material Partly Organic. — Apatite of Canada, amethyst, topaz 

 of Brazil, etc. 



jil. Coloring Matter Chiefly Inorganic. — Ruby, sapphire, spinel, beryl, etc. 

 The percentages of carbon and hydrogen were determined quantitatively. 

 An interesting series showing the relation of color to these percentages is that 

 below : 



Per cent. C. Per cent. H. 

 Violet fluorite of Wolsendorff, 0.017 0.0038. 



" " " Schneeberg, 0.014 0.0038. 



" /' Weardale, 0.010 0.008. 



Blue and green " " Cumberland, 0.009 0.002. 



Green " " Beaiyolais, 0.0095 0.0025. 



" " Hesselbach, 0.008 0.001. 



Yellow " " Dunham, 0.007 0.0025. 



Colorless " " Cumberland, 0.00 0.00. 



A. J. M. 



Tutton, A. E. Ein compensations Interferenz- In order to determine the thermal 

 dilatometer. Zeit. f. Kryst. 32: 1:20, iSqq. . . , . .- . , ^ , 



^ J 7 ^y expansion m plates of artificial crystals 



not usually thicker than 5 mm., Mr. Tutton has added to the Benoit Platinum- 



