C. H. Warren — Calcium Carbide. 



121 



pocket lens show on their surface a series of minute lines 

 or ridges, which run parallel or at 45° to the intersections 

 of the rectangular cleavages. If a cleavage fragment be 

 viewed in a good light, it -may be seen, particularly near 

 the edges where some light penetrates the fragment, that 



Fig, 1. — Sketch of a calcium carbide cleavage fragment. Cleavage is 

 parallel to the three pinacoids and pseudo-cubic in character. The carbide is 

 polysynthetically twinned; the twinning directions make with the pinacoidal 

 edges angles of approximately 45°, the twinning is therefore pseudo-dodeca- 

 hedral. The twinning lamellae may often be seen in freshly broken frag- 

 ments near the translucent edges. An attempt to illustrate this is made in 

 the figure. The directions followed by the lamella on any one cleavage face 

 are shown by the figure in the lower corner. 



there are within the substance series of exceedingly thin 

 lamellae, distinguished by reason of slight differences of 

 color or transparency, which are either parallel, or 

 inclined at approximately 45° to the cleavage edges. The 

 rectangular lines on the cleavage face mark the boundaries 

 of individual lamellas where these emerge on the cleavage 

 surface. The individual grains of carbide appear, there- 

 fore, at the outset to be in no sense simple individuals 

 but highly composite in character, being made up of a 

 series of thin plates united in a definite but complex 

 manner. The accompanying sketch will serve to illus- 

 trate the structures described (Fig. 1). 



