384 
PROFESSOR F. D. ADAMS AND DR, J. T. NICOLSON 
ments, to be so hard that a steel wedge had to be employed to split it. The ends of 
the column were found to be nearly black in colour from the deposition upon them of 
a thin ferruginous coating, derived apparently from the inner surface of the iron 
accumulator by means of which the water had been forced through the rock, as a 
similar deposit was found lining the tubes conveying the water both to and from the 
marble. This deposit, which is probably identical with that above referred to as 
coating the surface of the marble, was found upon examination to be composed of 
oxide of iron, a few little flakes of copper, carbonate of lime, and some material 
insoluble in acids, probably derived from the evaporation of the water on entering the 
heated portion of the apparatus. 
In the thin ferruginous coating on the end of the column, and thus immediately 
beneath the face of the piston, a few minute flecks of metallic copper were also 
visible, showing that a little copper had been dissolved from the copper pipe carrying 
the water from the accumulator and redeposited on the surface of the marble. This 
coating although less pronounced was also visible around the sides of the column 
where it was in contact with the heated iron tube enclosing it. It penetrates into 
the marble for a short distance at one or two spots at the top and bottom of the 
column, but is not seen elsewhere in the inner part of the marble. 
On splitting open the marble column, cones could be seen within it at either end, 
but they were not very sharply defined. The deformed portion of the marble, that is 
to say, the portion of the column not included in the cones, presented the same dead 
white or chalk-like appearance noted in former experiments. One of the halves of 
the deformed limestone column after being; freed from the iron tube was tested in 
compression in an Emery testing machine. The pressure was raised gradually with¬ 
out developing any signs of distress in the marble until a load of 3090 lbs. had been 
reached, when a minute crack developed. The pressure was then gradually increased 
to 3240 lbs., when the column suddenly crushed. In breaking down it split from top 
to bottom, like a perfectly homogeneous body, and without reference to the above- 
mentioned cones. Two columns of the same marble employed in the experiment and 
of the same dimensions as the original column, when similarly tested, broke suddenly 
by shearing, under loads of 4870 lbs. and 5760 lbs. respectively. These figures, how 
ever, cannot be used for the purpose of comparing the strength of the limestone 
before and after compression, as in the experiment at present under consideration, the 
bulge given to the marble was so considerable that with material of equal strength 
the new form would certainly be considerably stronger than a half-column of the 
original dimensions. In order to make a direct comparison, however, a fragment of 
the original marble was cut into the form of a bulged half-column of the same 
dimensions as that produced in the present case by compression. This when tested 
in compression suddenly sheared to pieces when the pressure rose to 3050 lbs. 
While, therefore, the averages of a number of trials would be required to establish 
the exact relative strength of the original marble and the marble after deformation. 
