stokes.] SUMMARY OF RESULTS. ±7 
The values of p obtained were: 
1. 3. 
Pyrite . 94.0 90.7 
Marcasite . 84. 6 86. < 
The duplicate results are therefore not sufficiently concordant, nor 
is the difference between pyrite and marcasite great enough, to give 
the method more than a confirmatory value. The difference here, as 
in the case of oxidation by the ferric-sulphate method, is due to the 
greater ease with which marcasite is attacked, but the relative oxida- 
tion rate of the sulphur is clearly much greater. The difference might 
possibly be greater al L00°, but here the experiments failed because 
of the strong tendency of the permanganate to deposit peroxide, even 
in the presence of much sulphuric acid. 
XIV. SUMMARY OF RESULTS. 
The chief results of this investigation may be thus summarized: 
1. When pyrite or marcasite is boiled with an excess of a solution 
of ferric, salt to complete reduction of the hitler the ratio of sulphur 
oxidized to mineral decomposed is perfectly definite and characterisl ic 
of each mineral, provided certain standard and easily controllable 
conditions are observed. Under these conditions the percentage of 
sulphur oxidized in pyrite is about 60.4 per cenl and in marcasite 
about is per cent of the total sulphur. These figures are the charac- 
teristic oxidation coefficients. 
2. The oxidation of pyrite or marcasite to ferrous salt, sulphuric 
acid, and free sulphur can nol be expressed by any single equation, 
but takes place according to two or more, the relation between which 
varies with the special conditions. 
3. An empirical curve for the oxidation coefficients of mixtures of 
pyrite and marcasite is constructed by aid of which the composition 
of naturally occurring mixtures may be quantital Lvely determined. 
4. The influence of various impurities on the results is described. 
5. Various concretions and other specimens are examined, and it is 
shown that in many cases much uncertainty exists in distinguishing 
pyrite and marcasite by the usual methods. 
(5. There is no well-established evidence of the existence of true 
paramorphs of pyrite after marcasite or of marcasite after pyrite. 
7. The hypothesis that most natural specimens, even when well crys- 
tallized, are intimate mixtures of the two is without foundation. 
8. Specimens crystallizing in the regular system are true pyrite, 
while those forming rhombic crystals are true marcasite. When the 
two are mingled or intergrown it is generally possible to distinguish 
each by the color after cleaning with acid, a rule to which there are 
a few exceptions. 
9. The density does not afford a trustworthy means of determining 
one mineral in the presence of the other. 
Bull. 186—01 4 
