CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY 
EXPERIMENTS RELATIVE TO THE CONSTITUTION OF PECTOLITE, PYR0PIIYLL1TE, 
CALAMINE, AND ANALCITE. 
By F. W. Clarke and George Steiger. 
In a series of investigations by Olarke and Schneider, which were 
carried out in the laboratory of the United States Geological Survey 
between 1889 and 1892, 1 a number of reactions were examined which 
shed some light upon the constitution of several natural silicates. The 
work then begun was unfortunately interrupted for several years; but 
it is now resumed, with the hope that it may be pushed considerably 
further. 
Two of the reactions studied by Clarke and Schneider were of peculiar 
interest. First, in the case of talc, it was found that one-fourth of the 
silica could be liberated by ignition; and that the fraction thus set free 
was measurable by solution in aqueous sodium carbonate. This reac- 
tion suggests that other acid metasilicates may behave in a similar 
way, and that we perhaps have a means of discrimination between such 
salts and other compounds which simulate them. In other words, an 
acid metasilicate may be experimentally distinguished from a pseudo- 
metasilicate by the way in which it splits up when ignited. Evidence 
bearing upon this supposition will be found in the present paper. 
The second of the reactions just referred to is that between dry 
ammonium chloride, at its temperature of dissociation, and various 
silicates. 2 This involves, in part at least, the action of dry gaseous 
hydrochloric acid upon the compounds which are studied: and different 
minerals are very differently attacked. Some are almost completely 
decomposed, others are affected but slightly; and here again there 
seems to be a method of diagnosis which deserves further attention. 
Both reactions suggest the main purpose of the investigation; which 
is, the fractional analysis of silicates by means of various reagents, in 
iBull. 17. S. Geol. Survey No. 78, p. 11: Bull. No. 90, p. 11 : Bull. No. 113, p. 27. 
2 Bull. U. S. Geol. Survey No. 113, p. 34. 
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