Journal 



OF THE 



NEW-YORK MICROSCOPICAL SOCIETY. 



Vol. II. JUNE, 1886. No. 6. 



THE MICROSCOPICAL STRUCTURE OF THE IRON 



PYRITES. 



BY ALEXIS A, JULIEN, PH.D. 

 {Read Mayjth, \'i>'i,b.) 

 In the black mud of ditches and pools, and of the flats ex- 

 posed at low tide, in the muck of salt-marshes and the peat of 

 fresh-water swamps, in the soil, in the very mud between the 

 stones in the pavements of our streets, there is a substance con- 

 stantly present and yet very unfamiliar, of whose office in 

 nature, or even of whose very existence, man rarely becomes 

 conscious. Continually formed by the contact of iron oxide 

 with the sulphur separated from decaying organic matter, it is 

 yet in the highest degree unstable, and continually in a state of 

 decomposition back again into its two constituents, under the 

 action of the air and of vegetable acids. Then the fetid vapors 

 of hydrogen sulphide which it evolves testify decidedly to its 

 existence, at least before the court of one of our senses — some- 

 times as an offensive stench, when these vapors rise from a ditch 

 in a Long Island or a New Jersey salt-marsh — and sometimes as 

 a rather welcome though quaint odor, delightfully associated 

 with all the mirth and music and sanitary expectations of a 

 summer visit to the Sulphur Springs of New York or Virginia. 

 On the other hand, mineralogists recognize that this substance 

 rarely, if ever, becomes concentrated in masses visible to the 

 eye, never crystallizes, and is never found as a pure, isolated 

 mineral, except, strange to say, within some meteorite which 

 falls from the sky, and shows among its constituents dark 

 rounded grains of the same material in the form of troilite. 

 Even its innumerable black particles, scattered through the 

 marsh-mud, are dull and amorphous, and almost always indis- 

 tinguishable under the microscope, resembling mere granules of 



