. py 
1877.] 257 [Frazer. 
Very little of the precipitate was observed upon the surface of the 
powder, the rapidity of the chemical change being proportional to the ex- 
tent of surface in contact with air, and probably to the strength of the so- 
lution. The fact that the fluid exhibited no signs of acid reaction is suffi- 
cient proof that for every molecule of iron hydrate thus set free one atom 
of calcium took its place as a sulphate. 
To test whether this exchange was effected by the intermediate pro- 
duction of iron bicarbonate, and the decomposition of this at its contact 
with air, the fluid was examined for carbonates in solution, but none were 
detected. 
It seems probable then that in presence of bodies of limestone and free 
oxygen, iron sulphate is decomposed and its base precipitated at the ex- 
pense of the calcium in the limestone. 
Another experiment was tried to ascertain the amount of diffusibility of 
this solution of iron sulphate. 
Another beaker of about 1 liter capacity was placed by the side of the 
first, and filled with water. A piece of large French filtering paper having 
been rolled up, the ends were immersed in the respective beakers. After 
standing for 24 hours with the fluid in the beakers at about the same level, 
the contents of the beaker last employed were tested without finding a trace 
of iron in it. 
A gum tube of about 30 mm. internal cross-sections was then bent, 
filled with water, the ends stopped by the thumbs, and placed beneath 
the surface of liquid in the respective beakers. 
After two hours of this syphon connection, the contents of the second 
beaker were again tested without finding any traces of iron.* 
In connection with this subject several years ago I sought to explain the 
chemical reactions involved in the production of limonite by means of 
limestone in the following four chemical equations from pyrite (though I 
never have considered it necessary to assume that pyrite was the only fer- 
riferous mineral concerned in this production). 
Fe 8, + 0, + H,O in presence of oxygen, water and 
limestone. O + H,O + CaCo, 
ee ete Up oxyacr and one) = FeSO, + H,SO, [Ox, Aq. limestone. ] 
molecule of H,O ) 
b. By decomposing 1 molecule of) = = FeSO, + CaSO, + CO, + H,O 
CaCO 5” [Ox, Aq. limestone. ] 
c. By decomposing one molecule ‘, 
of CaCO, and absorbing 1 -= Renee Faia 
molecule of H,O quel “A 
d. By oxidation in air (twice) _ (CaSO,), + H Fe,0, + (CO,), 
the previous) See [Ox, Aq. limestone. } 
It now appears however, that the intermediate stage of iron bicarbonate 
is not necessary, but that the oxide may be directly produced after the hy- 
*The same experiment was tried, alter the beakers had been connected by a 
column of water for over a week, with he same result. 
PROC. AMER. PHILOS. Soc. xvVII. 100. 2F. PRINTED FEB. 2, 1878. 
