Washington, D. C. v November 6, 1922 
x 
TABLES FOR THE MICROSCOPIC IDENTIFICATION 
OF INORGANIC SALTS. 
By Wittiam H. Fry, Scientist in Chemical Investigations, Bureau of Soils. 
CONTENTS. 
Page. Page 
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Petrographic methods. ............-.-.------ 2} fPablesaossrt 3. s2sass teseses os iclbesge5s1 3. 10 
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INTRODUCTION. 
The identification of a salt by a qualitative chemical analysis 
necessarily presupposes the purity of the salt, since a qualitative 
analysis would make no distinction between an accidental impurity 
and a constitutional molecular group of the compound. But even 
with material of assured purity the results of the analysis would still 
be indefinite. Whether, for example, a substance containing K, H, 
and PO, was a monopotassium or dipotassium phosphate would be 
undecided. The whole question of hydrates would likewise be inde- 
terminate. If the material qualitatively examined should be a mix- 
ture, the difficulties of identification would be insuperable by the 
analytical evidence alone. 
Ifa quantitative anal» sis is made, the results would be sufficiently 
explicit im certain relatively simple cases if the material analyzed is 
known to be a single pure substance. But in other cases—for example, 
elemental suiphur—the analysis would give no eyidence as to the 
particular allotropic form of sulphur—a pomt which in certain 
problems might be of considerable importance. Where the substance 
is a double salt, the analytical data would not differentiate between a 
double salt and a mixture of two simple salts; and the more com- 
plicated the molecular composition of the salt the more difficult would 
be the interpretation of the analysis. With mixed salts any calcu- 
1531—22— Bull. 1108-1 
