THE SMOKE NUISANCE 245 



beauty of the outline, causing considerable alteration of the original 

 forms and making the building degenerate into a mere mass of dirty, 

 shabby masonry. 



It is rather interesting to note the vogue of such materials in build- 

 ings as glazed brick and terra cotta, in smoky cities. Stone, for which 

 they are substitutes in many cases, is injured by smoke and the asso- 

 ciated products of combustion in two ways: 



1. The soiling of the surface, so that in the course of a few months 

 all stone takes on the same gray, grimy color. This means either the 

 loss of all artistic effect that may have been obtained by color contrast, 

 etc., or the frequent cleaning of the building, which is an additional 

 expense and at the same time aids in the destruction of the stone. 



2. The actual destructive action on all stones by the acid products 

 of the combustion of the coal. This is especially marked on any stone 

 containing calcium or magnesium carbonates in larger or smaller quan- 

 tities. Although there is some action on other constituents of the build- 

 ing stones, it is so slow in most cases as to be hardly noticeable. 



A study was made in connection with the smoke investigation of 

 the Mellon Institute as to the effect of smoke on outside painting. 1 

 Both the effect on paint as a protective coating and as a decorative cov- 

 ering was considered. It was found that some paints last comparatively 

 longer in Pittsburgh than in many other cities. This is in part due to 

 the protective action of the soot in preventing the destructive action of 

 the active rays of the sun. This would also indicate that such paints 

 might afford a lodging place for fungi, which grow in the absence of di- 

 rect sunlight. 



It was found that smoke darkens paint coatings very rapidly and 

 renders the use of light colors unsatisfactory on account of the short time 

 they retain their true color. Analyses of the surface of the paints 

 showed that the darkening was due to sulphur dioxide gas and to the 

 accumulation of soot, carbon and similar organic matter contained in 

 smoke. 



The effect of smoke on metals must be taken into consideration in 

 connection with the other building materials. When soot containing 

 tar comes in contact with a metallic surface, it is made to adhere more 

 or less firmly by means of its tar content. The occluded acids, prin- 

 cipally sulphuric and sulphurous, are thus brought in intimate contact 

 with the metal, giving a much better chance for corrosive action to take 

 place and for it to become complete quicker than if the same amount of 

 acid dissolved in rain water came in contact with the metal. The acid 

 in the rain water drains off readily, while the soot protects the occluded 

 acid to a great extent, so that it remains in contact with the metal until 

 it has all been used up. 



1 Benner, Eaymond C, Bulletin No. 6, "Papers on the Effect of Smoke on 

 Building Materials," 1913. (Published by Mellon Institute.) 



