OF ZINC AND ANTIMONY. 



341 



generally with both sets of lateral edges truncated. The crystals almost invariably, so 

 far as I have observed, run out to fine points, and although I have examined many 

 hundreds, I have only met with a very few having the basal plane O, and with none 

 on which planes modifying the basal edges could be distinguished. It was, therefore, 

 only possible to ascertain the relative size of the lateral axes. This is given below un- 

 der Fig. 2. Fig. 1 exhibits the general form of the isolated crystals supplying the 

 terminal plane 0. 



I on i 1 = 148° 30'. 

 lonil = 121° 30'. 

 IonI= 117° or 63°. 



I in 1 on I in 2 = 117°. 

 ii in 2 on I in 1 = 121° 30'. 

 i Tin 1 on I in 1 = 121° 30'. 



The faces of the crystals are generally striated, but from a quantity of them several 

 can almost always be obtained whose faces reflect a very well defined image, so that 

 the angles can be measured with the greatest accuracy. The angles as above given 

 measured the same on a large number of crystals from several different crystallizations, 

 and in cases where a variation from them Avas observed it was evidently the result of 

 striation or of some imperfection. The measurements were made in a darkened room, 

 using as a signal a narrow horizontal slit in the screen which covered the window illu- 

 minated by the sun. This simple arrangement, for which I am indebted to Professor 

 Miller of Cambridge, England, enabled me to determine the angles even of the smallest 

 crystals with great precision. The isolated crystals of SbZuj obtained as described 

 above are small, a few tenths of a line only in diameter, and not generally over an inch 

 in length. They tend, however, to form compound crystals with parallel axds, which 

 are often several inches in length, and a quarter of an inch or more in diameter. Fig. 

 2 is a section of a very well formed double crystal, on which all the angles were accu- 

 rately measured. A few of these angles given beneath the figure show that the 



