THE CORROSION OF BUILDING STOXE3. 283 



manufactories that throw still more acid into the air immediately 

 surrounding them. 



As an example of the action of the atmospheric acids of London 

 upon building stones, I have but to name the Houses of Parliament, 

 which have only been rescued from superficial ruin by the patchwork 

 replacing of certain blocks of stone, and various devices of silicious 

 and other washings that have been carried out at great cost to the 

 nation. That such an unsuitable material should have been used is 

 disgraceful to all concerned. The ruin commenced before the build- 

 ing was finished. At the time when its erection commenced there 

 were abundant evidences of the ruinous action of London atmosphere 

 on some kinds of stone and the capability of others to resist it, for 

 while many modern buildings are peeling and crumbling, some of the 

 oldest in the midst of the city show scarcely any signs of corrosion. 



The Birmingham and Midland Institute was established and in 

 practical operation a few years before the present noble building was 

 erected. I was the first teacher there and conducted the Science 

 classes in the temporary premises in Cannon Street. Having ob- 

 served with some interest the disintegration of St. Philip's Church 

 and other buildings, I was anxious for the safety of the new Institute 

 buildings, and accordingly made some experiments upon the material 

 proposed to be used by the architect. My method of testing was 

 very simple, and as the practical result has verified my anticipations 

 I think it might be adopted by others. 



First, I immersed some lumps of the stone in moderately strong 

 solutions of sulphuric and hydrochloric acids successively, and ob- 

 served whether any visible action occurred after some days. There 

 was none. I then roughly tested the crushing pressure of small sam- 

 ples in their natural state, and subjected similar sized pieces to the 

 same test after they had been immersed in the acids. I found thus 

 that there were no evidences of internal disintegration even after 

 several days' immersion, and therefore inferred that the stone would 

 stand the acid vapors of the Birmingham atmosphere. This has been 

 the case with that portion of the building that was built of the mate- 

 rial I tested. As I know nothing of the stone which is used for the 

 extension of the building under the present architect, Mr. Chamber- 

 lain, I am unable to make any forecast of its probable durability. 



The experiments I made at the time named with this and other 

 building materials justified the conclusion that the worst of all mate- 

 rial for exposure to acid atmospheres is a sandstone, the particles of 

 which are held together by limestone, or are otherwise surrounded 

 by or intermingled with limestone ; and that the best of ordinary 

 material is a pure sandstone quite free from lime. I do not here 

 consider such luxurious material as granites or porphyries. 



Compact limestone, such as good homogeneous marble, stands 

 fairly well, although it is slowly corroded. The corrosion, however, 

 in this case, is purely superficial and tolerably uniform. It is a very 

 slow washing away of the surface, without any disintegration such as 

 occurs where a small quantity of limestone acts as binding material 

 to hold together a large quantity of silicious or sandy material, and 

 where the agglomeration is porous, and the stone is so laid that a 

 downward infiltration of water can take place ; for it must be remem- 

 bered that although the acid originally exists as vapor in the air, it is 

 taken up by the falling rain, and the mischief is directly done to the 



