292 Penfield and Foote — Clinohedrite. 



The crystals exhibit very distinctly the phenomenon of pyro- 

 electricity when tested with the red oxide of lead and sulphur 

 method described by Kundt.* On cooling a crystal of the 

 type represented by figs. 1 and 2 the p, e, and the upper 

 extremities of the m faces in front became positively electri- 

 fied and attracted the particles of sulphur, while the diagonally 

 opposite faces %, y, p x , e^ and the lower extremities of m x 

 became negatively electrified and attracted the red oxide of 

 lead. 



A section parallel to the pinacoid 010 when examined in 

 polarized light showed an extinction of about 28° from the 

 vertical axis in the obtuse angle /3, and this direction corre- 

 sponds to 6. The plane of the optical axes is at right angles 

 to 010. The crystallographic axis b is the obtuse bisectrix, and 

 corresponds to c. The double refraction is not very strong, 

 and is negative. 



Material for the chemical analysis was first carefully selected 

 by hand picking, and was then further purified by pulverizing 

 and separating by means of the barium mercuric iodide solu- 

 tion. That portion which was used for the analysis varied in 

 specific gravity between 3*34:4 and 3*327. 



The method of analysis was as follows : Water was deter- 

 mined as loss on ignition, and the residue, after fusion with 

 sodium carbonate, was dissolved in hydrochloric acid. The 

 solution was evaporated twice to separate the silica, and in the 

 filtrate from the silica the acid was neutralized with a slight 

 excess of ammonia, formic acid of specific gravity 1*12 was 

 added so as to make about one-fourth of the final volume, and 

 hydrogen sulphide was passed into the hot solution until the 

 zinc was precipitated. After filtering, the zinc sulphide was 

 dissolved in hydrochloric acid, and the zinc reprecipitated as 

 carbonate and weighed as oxide. In the filtrate from the zinc 

 the small quantities of iron and alumina were precipitated 

 twice with ammonia. To the filtrates acidified with hydro- 

 chloric acid bromine was added, and on making alkaline and 

 heating to boiling all of the manganese was precipitated, but 

 as it carried a little calcium it was redissolved, precipitated 

 from an acetic acid solution with bromine, and finally deter- 

 mined as pyrophosphate. Calcium and the trace of magnesium 

 were separated and determined in the usual manner. 



The results of the analysis by Foote are as follows : 



* Ann. d. Phys. u. Chem., xx, p. 592, 1883. 



