328 Spectroscopic Examination of Silicates. 



seam between talc upon one side and oligoclase-felsite on the 

 other, gave a decided lithium band. The mineral occurs 

 in brownish scales, orthorhombic in form, and optically 

 biaxial. A quantitative determination afforded 0-41 per 

 cent, of lithia and soda. The pure alkaline chlorides ob- 

 tained in the course of the analysis, and which together 

 weighed 0*009 grm., were carefully tested and found to con- 

 tain no potassium whatever, but to consist entirely of lithium 

 and sodium. The calcic chloride process is thus valuable in 

 showing the isomorphic replacement of one element by 

 another. For in a mineral very similar to the one above 

 described, except that it crystallizes in broad plates instead 

 of small scales, and which has been called jefferisite by 

 Prof. Brush, lithium appears in many instances to take the 

 place of potassium. The analysis of jefferisite by Prof. 

 Brush (Dana's Min., p. 494), gives soda trace, potassa 0-43 

 per cent. A large number of jefferisites, from the serpen- 

 tine quarry three miles southwest of Westchester, Pa., 

 afforded only the lithium band with calcic chloride paste. 



In the above instance, I neglected to separate the alkalies. 

 But in the case of a mineral resembling ripidolite, and oc- 

 curing in connection with the corundum at Unionville, Pa., 

 I have made the determination and found that, in certain 

 cases, this method is of surprising delicacy. This bluish- 

 green variety of ripidolite gave the lithium band very dis- 

 tinctly. It contains only 0-11 per cent, of lithia and 0*14 

 per cent, of soda. The pure chlorides obtained in the 

 course of the examination were tested, and found to contain 

 not the slightest trace of potassium. As only 0-005 grm. of 

 the ripidolite was employed, the spectroscopic examination 

 which required two minutes to perform, revealed the pres- 

 ence of the one two hundred thousandth part of a gramme 

 of lithia. 



It would be unsafe to infer from this statement that the 

 calcic chloride process is equally delicate in the case of every 

 mineral, and of every element capable of manifesting itself 



