48 
The black powder attracted by the magnet yielded by analysis 
5*78 peroxide of iron, from 6*01 of substance ; while, had the sub- 
stance been magnetic oxide of iron, the amount of peroxide yielded 
would have been 663; so that we may safely conclude that the 
substance was nothing more than magnetic oxide of iron, produced 
during the fusion with the alkaline carbonate. 
The next experiment that suggested itself was to try the action 
of more concentrated acid upon the supposed clay. The whole of 
the substance immediately dissolved in moderately strong hydro- 
chloric acid, with the evolution of much carbonic acid gas ; the so- 
lution on analysis yielded a large quantity of protoxide of iron, 
together with carbonate of lime, and traces of sulphate of lime, also 
alumina, magnesia, and soda. 
As a conclusive experiment, the action of carbonic acid gas upon 
the substance suspended in water was tried. Upon filtering the 
liquid at the close of the experiment, and subsequently analyzing it, 
much protoxide of iron was dissolved. 
It is obvious, from the foregoing remarks, that the pieces of sub- 
stance found disseminated through the stone consist entirely of proto- 
carbonate of iron. 
The ill effects of these nodules of proto-carbonate of iron are at 
once evident ; for a block of stone freshly cut from the quarry exhi- 
bits no external mark of their presence within it to guide us, and it 
is not until the rain and air have had their full effect upon it for some 
time that the stain renders itself visible as a dark reddish-brown 
ring of peroxide of iron. 
