CH. VI] MICRO-CHEMISTRY 181 



There is formed Ferric acetate, Ammonium chlorid and double chlorids of 

 ammonium and iron. Study the preparation and observe the following points. 

 I. Tendency toward formation of double salt. 2. That the type crystal of 

 NH 4 C1 is a cube. 3. Cubes may so grow as to present the appearance of a 

 rectangular prism. 4. In certain positions cubes have the appearance of a 

 pyramid'. 5. In other positions they exhibit a hexagonal outline, thus simu- 

 lating a polyhedron of many faces. 6. There is scarcely any tendency in 

 this case toward the formation of the dendritic masses observed in the first 

 experiment. 7. The crystals often develop fastest along the diagonal planes 

 so that the regular faces are replaced by pyramidal depressions." 



Fig. 141. Czapski's Ocular Iris-diaphragm with cross 

 hairs for examining and accurately determining the axial 

 images of small crystals. The iris diaphragm enables the 

 observer to make the field as large or small as desired. 



A. Longitudinal Section. 



B. Transection, showing the cross lines and the iris 

 diaphragm with the projecting part at the left, by which 

 the diaphragm is opened and closed. {Zeiss' Catalog. ) B. 



For directions and hints in micro-chemical work and crystallography, 

 consult the various volumes of the Journal of the Roy. Micr. Soc. ; Zeitschrift 

 fur physiologische Chemie, and other chemical journals; Wormly; Klement 

 & Renard; Carpenter-Dallinger; Hogg; Behrens, Kossel und Schiefferdecker; 

 Frey; Dana, and other works on mineralogy; Davis, Behrens, T. H. — Anleitung 

 zur micro-chemischen Analyse der wichtigsten organischen Verbindungen. 

 Hamburg, 1895-1897. Microchemische Technik, 2d edition, Hamburg, 1900. 

 A manual of michrochemical analysis with an introductory chapter by J. W. 

 Judd, London. 1894. 



Especial attention is also called to the articles of Dr. E. M. Chamot 

 in the Journal of Applied Microscopy beginning with vol ii. p. 502, and contin- 

 ued in vol iii. and iv. 



TExTLLE, FIBERS, FOOD AND PHARMACOLOGICAL PRODUCTS 



§ 255. Textile Fibers. — The microscope is coming more and more into 

 use for the determination of the character of textile fibers, both in the raw state 

 and after manufacture. As the textile fibers have distinctive characters it is 

 not difficult to determine mixtures in fabrics of various kinds. The student is 

 advised to study carefully known fibers, as of cotton, wool, linen, silk, jute 

 etc., so that he is certain of the appearances, and then to determine of what 

 fibers different fabrics are composed. He will be astonished at the amount of 

 ■"Alabama wool" in supposedly all wool goods. 



