THE ALKALINE REACTION OF SOME NATURAL SILICATES. 
By F. W. Clarke. 
That pure water exerts a distinct solvent action upon many natural 
silicates lias long been known. As far back as 1848 the Rogers broth- 
ers published a series of observations upon this subject, 1 and showed 
that some species of minerals would give an alkaline reaction to test 
paper. They did not, however, give details concerning the individual 
minerals thus investigated. The more recent researches of Daubree 
and of Oossa are well known. 
By the use of phenolphthalein as an indicator the alkalinity of many 
silicates can be demonstrated with the utmost ease, and the experi- 
ments described below serve to bring out very clearly the relative 
decomposability of certain minerals and rocks by pure water. The 
method adopted was as follows: A series of glass-stoppered bottles was 
placed against a white background. In each bottle half a gram of finely 
pulverized mineral was put, and then 50 cubic centimeters of distilled 
water, containing a very little alcoholic phenolphthalein, was added. 
As the indicator was mixed, once for all, with the total amount of water 
taken for the entire series, the 22 samples examined were treated exactly 
alike. Two of the bottles were filled with the water and indicator in 
blank, in order that possible action upon the glass itself might be 
detected if it occurred. The two blanks, however, remained colorless 
during the two weeks through which the experiments lasted. The 
results obtained were as follows: 
Muscovite. — A doubtful trace of coloration, which soon disappeared. 
Lepidolitc, — Like muscovite. 
Phlogopite. — The peculiar noniluoriferous variety from Edwards, New 
York. Gave a very distinct, permanent pink coloration. 
Orthoclase. — A trace of coloration which increased for a few days and 
then faded. 
Oligoelase. — The transparent variety from Bakersville, North Caro- 
lina. Distinct and permanent, but pale coloration. 
Albite. — From Amelia County, Virginia. Gave a good, permanent, 
alkaline reaction. 
Leucite. — A slight reaction at first, which faded in a few days. 
Nephelite. — The eheolite from Litchfield, Maine. Good coloration, 
but partly fading in time. 
'Am. Jour. Sci., 2nd series, Vol. V, p. 401. 
156 
