= 
Frazer. | 256 [Dee. 21, 
In opposition to the chemical hypothesis of the origin of these limonites, 
it is only just to cite the occurrence at Bull’s Run (five miles south of 
Wrightsville, York County), amongst the calciferous slate, and even the 
limestone itself, of unusually large Pyrite crystals still in a perfect state of 
preservation, though under conditions very favorable to metamorphosis. 
Perhaps the generally gentler dip of the strata at that point protected the 
pyritiferous layers from the percolation ; or perhaps some other cause may 
account forit ; or perhaps the whole idea of the chemical production of 
limonite is erroneous, though in its support may be mentioned the results 
of the following experiments : 
About 20 grams of crystallized ferrous sulphate were dissolved in 100 ce. 
of water. 
About 50 grams of crystalline limestone were then ground up into fine 
powder, and placed in a glass stoppered bottle, into which 50 cc. of water 
was poured. 
Ten ce. of sulphuric acid of density about 1.7 were then added, and 
the contents agitated. After the effervescence had subsided, the iron solu- 
tion was poured into the same beaker, and the contents again strongly agi- 
tated. 
After the subsidence of the powdered carbonate of lime, and upon it the 
light precipitate of calcium sulphate, the liquid was left undisturbed. It 
gave at first a feeble acid reaction, but later became quite neutral. 
From time to time in the course of 24 hours the bottle was shaken, and 
the sediment again allowed to subside. 
A light film of iron hydrate began to be perceptible in a few moments 
after the first shaking, and was quite perceptible both as a layer above the 
calcium sulphate, and as a ring which formed around the interior of the 
flask at the surface of the contained liquid. 
This can be observed in the flask which I have brought here, the yellow- 
ish brown ring occurring at about the height of the upper surface of 150 
ec in this bottle. 
It suggested itself that possibly this action might result from the oxida- 
tion of the iron solution and precipitation at the surface. To test this the 
bottle containing the substances above described, was plaeed in a beaker 
of about 1.5 liter capacity, and water was carefully poured into the latter 
so as to overflow and finally submerge the lip of the bottle about 3 cm be- 
low its surface, the solution from this time being left undisturbed. 
In the course of 24 hours or less there was a very copious flocculent pre- 
cipitate of iron hydrate in the bottom of the beaker, and on the sloping 
neck of the bottle while the surface of the fluid was covered with an irides- 
cent film like that on many natural chalybeate waters. 
This experiment seemed to show that in presence of limestone the neu- 
tral sulphate of iron is readily decomposed in contact with atmospheric air, 
and the sediment precipitated as a flocculent mass from the upper surface 
of the fluid. 
The reaction of the solution was entirely neutral. 
