) 
CONTENTS 
Pago. 
Lett er of transmittal, by Dr. Becker 9 
I. Uncertainty of methods of distinguishing pyrite and marcasite 11 
Crystalline form . . ... 11 
Color.... 11 
Density . . 12 
Density according to different authorities 12 
Density not a sure criterion of composition . .. ... 12 
Oxidation. 13 
Pen field's method . . 14 
Action of copper sulphate on pyrite and marcasite ...... 14 
II. Behavior of pyrite and marcasite toward ferric solutions. .. . 14 
Action of ferric chloride ... . . . . 15 
Percentage of sulphur oxidized .. 15 
Ferric sulphate oxidation method . 15 
Principle of the method 15 
Deduction of an expression for oxidized sulphur. ... 16 
Standard solution and temperature 17 
Oxidation coefficient .. .. . 17 
Theory of the reaction 17 
Influence of concentration _ 18 
Influence of temperature. .... . . .... 18 
Reason for the different behavior of pyrite and marcasite 19 
Further applications of the method ....... . . 20 
III. Details of the method 20 
Necessary precautions ..... ... 20 
Preparation of the material . . 20 
Oxidation apparatus . . 22 
Details of the operation .. 2:') 
Accuracy of the method . . . 24 
IV. Data for pyrite 25 
Table, and description of specimens _._. 25 
( )xidation coefficient of pyrite 25 
V. Data for marcasite 25 
Table, and description of specimens. ... 26 
Oxidation coefficient of marcasite . . 27 
VI. Mixtures of pyrite and marcasite - 27 
Conditions under which the oxidation coefficients of mixtures may be 
determined ... . . . ... . . 28 
VII. Data for artificial mixtures .. .. 29 
Discussion of the curve shown in PI. I ... . 30 
Influence of the minimum: indirect determination of small amounts 
of pyrite in marcasite 30 
5 
