rs 
wee 
4 Experiments on American and Foreign Building Stones. 
oxyd of iron derived from decomposed iron pyrites, many veins 
of which traverse it in various directions, and the skeleton crys- 
tals with loosely cohering nuclei are even more conspicuous than 
at the points where the rock crops out as above described. 
That even the fine-grained stone above mentioned is not in 
all respects suitable to be employed as the casing stone of large 
alr is proved by the present condition of the shaft of the 
Washington Monument in Baltimore, where a similar stone from 
the sane neighborhood was used. "This monument was com- — 
menced on the 4th of July, 1815, and the statue was elevated on 
the 19th of October, 1829. On the 23d of October, 1850, or 
twenty-one years from the date of its completion, I examined from 
5 the platform at the base of the shaft the condition of its lower part. 
There was seen on the side of the shaft opposite to the north- 
east corner of the base, a crack commencing near the bottom 
and following partly the joints of the masonry, and partly certain 
pat ha or vertical cracks crossing the blocks of marble. The 
, 5th, Sth, 10th, 11th, 13th, 14th, and 15th courses of stone, 
an from the bottom, were seen to be broken either partly 
or wholly across, and in one instance a block is broken into pris 
ieces. On the southeasterly side of the shaft is a secon 
“of fracture crossing ten or twelve blocks, mostly alternating with 
the courses of masonry which have joints corresponding with the 
general course of the fissure. At the southwesterly side are — 
fifteen blocks cracked either partly or wholly across, and form- 
ing a third fissure more or less ina zigzag pase controlled 
apparently in some degree by the joints of the masonry. On the 
west side a fourth line of fracture appears to ascend some forty or 
fifty feet, and on the northwest side still a fifth line perhaps some- 
what more irregular in direction than the preceding, but still 
easily traceable by the eye. In some cases where the cracks on two 
alternate blocks meet the joint of masonry in the course between 
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them, the opening of that joint is apparent; in other words the = 
crack is here in the cement, as might reasonably be expected. 
How long these cracks have existed, I have no means of ascer- 
taining. But one thing seems certain, that alternate cold and- — 
which bound them. Time will reveal the effects, and pers 
expose the causes of these incipient dilapidations. 
A chemical analysis of the “alum limestone” has been pu ; 
lished by te Dr, L. D. Gale, which makes the composition of that 
e 
sampl 
Carbonate of lime, ; . 2e6 
Silica or other insoluble matter, ? y is 
