ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 411 



manent Microscope mounts. The process is applicable to such metals 

 as are reducible from solution by some other metal. For the prepara- 

 tion of silver crystals, a small drop of a mixture of equal parts of a 

 10 p.c. solution of silver nitrate, and a concentrated solution of zinc 

 nitrate, is placed on a glass slip and spread into a thin film. A piece 

 of zinc is filed in such manner that the filings fall thinly over the 

 moist surface. Reduction begins at once, and each zinc particle be- 

 comes a centre of crystallization of silver. The preparation is kept in 

 a moist atmosphere until crystallization is complete, then allowed to 

 become nearly dry in the air, coated with balsam in xylol, dried in a dust- 

 free atmosphere, and covered in the usual way. With variations in 

 manipulation, the general process may be used for gold, copper, lead, 

 bismuth, tin, cadmium, and antimony. 



Photomicrographs indicate the appearance of the radiating, fern -like 

 crystals produced. 



Artificial Sillimanite.* — W. Eitel has examined, microscopically 

 and otherwise, the slags obtained by the ignition of a mixture of iron- 

 thermit and silica. Such slags, w 7 hich are crystalline, not vitreous, con- 

 sist essentially of silica and alumina, and contain crystals of the silicate 

 of alumina, sillimanite, strongly rese rbling the natural mineral. The 

 fibrous structure of the slag was due to the presence of long, very thin, 

 fibre-shaped crystals of sillimanite, but other forms occurred also. 

 Crystals of corundum were abundant in the slags. 



Metal-microscopy with Polarized Light. f — H. Hanemann has in- 

 troduced into the apparatus, previously described, modifications which 

 greatly facilitate the observations. The examination of metallic surfaces 

 by means of reflected polarized light yields information upon the optical 

 properties of the various constituents. The examination of the con- 

 stituents of numerous iron-carbon alloys indicated that ferrite and 

 austenite were isotropic, inartensite was feebly anisotropic, and cementite 

 was anisotropic. Austenite and martensite were thus shown to lie 

 distinct phases. 



• Zeitschr. Anorg. Chem., lxxxviii. (1914) pp. 173-84 (8 figs.), 

 t Zeitschr. Anorg. Chem., lxxxviii. (1914) pp. 265-8. 



