122 C. H. Warren — Calcium Carbide. 



Columnar structures (groups of parallel elongate col- 

 umns) are common, particularly in the coarser varieties. 

 The direction of elongation of the columns makes an 

 angle of 45° with the rectangular cleavages. The contact 

 surfaces between individual columns is wavy and 

 irregular. 



Microscopic character of electric furnace carbide. — 

 Small fragments of carbide were ground down on two 

 parallel sides with fine carborundum or rouge and dry 

 kerosene oil until sufficiently thin to transmit light. 

 Owing to the tendency of the carbide to break and cleave 

 when any considerable degree of thinness is reached, 

 these sections, in general, were not as satisfactory for 

 study as crushed material. 



Most of the preparations for study were prepared 

 either by crushing small fragments in a mortar under 

 some liquid which decomposes carbide slowly or not at all 

 (dry kerosene oil, a-monobrom-naphthalene or methylene- 

 iodide), and then transferring some of the powder with 

 the liquid to a glass slide and covering the Vhole with a 

 cover-glass; or a small fragment was carefully crushed 

 and the powder quickly passed through a fine screen (100- 

 150-200 mesh) on to a glass slide on which was a drop of 

 one of the liquids used, and the whole covered with a thin 

 cover-glass. 



Color. — The color in transmitted light is purplish-red 

 or lilac-yellow, and less commonly a slightly greenish 

 yellow. Exceedingly thin fragments appear nearly or 

 quite colorless. 



Pleochroism. — Slight differences of color (pleochroism) 

 for light vibrating in different crystallographic directions 

 may be seen, but only in relatively thick fragments. 



Transparency. — The transparency is good in thin frag- 

 ment (0.01 to 0.02). Thicker and larger fragments are 

 subtransparent to translucent. Many fragments are only 

 feebly translucent owing to deep color, inclusions and 

 twinning. 



Cleavage. — The cleavage is easy and perfect in three 

 directions at right angles to each other, as nearly as can 

 be determined under the microscope. The true rectan- 

 gularity of this cleavage was established by Professor E. 

 H. Kraus by measurements on the reflection goniometer. 



Tivinning. — The twinning is highly polysythetic. 

 Individual cleavage plates, ground very thin, show, par- 



