1885.] Ni;W YORK ACADEMY OF SCIENCES. 57 



{2) As to their Elements. — Tliese salts consist of carbonates, 

 suli)luites, nitrates, and chlorides of sodium, potassium, calcium, 

 magnesium, etc. Sometimes several of these salts arc associated 

 in one sample, taken from a building, and in nearly every 

 instance that has come to my notice, I have found a difference 

 of constituents and proportions; so much depending u])on the 

 clay and how it is burned, and the character of the limestone 

 used for the mortar or cement. Hence arise the apparently 

 contradictory statements and opinions expressed by chemists and 

 others as to what these salts are composed of, some claiming one 

 thing, and some another; and I have no doubt that each may 

 have been correct in his analysis, though, perha])s, widely differ- 

 ing from the others. I have taken two sam])les from the same 

 building, and found them dissimilar. I believe that every kind 

 of brick, cement, and mortar contains soluble saline ingredients. 



(3) The causes of their appearance. — This is wholly due to 

 moisture in the masonry. This dissolves the salts, forming a 

 weak brine which, upon coming to the surface, loses its water by 

 evaporation, and leaves the salt to crystallize and form the ob- 

 ]ectioiuible efflorescence. 



The presence of the moisture may be due to the water used in 

 mixing the mortar or cement, or in wetting the bricks; or it may 

 be absorbed from the rain falling against the walls. Hence the 

 drier the walls are kept during the erection of a building (con- 

 sistent with making the work good) the less chance will there be 

 for the salts to show themselves, and if the walls can afterwards 

 be kept perfectly dry, the salts remain inert and do no harm, be- 

 cause water is the agent that renders them active and effective 

 in their resolving ])owers. It may sometimes be seen which 

 parts of a building were built in dry weather and which in wet, 

 by the appearance of the mortar joints at different elevations, 

 especially on old brick structures. 



To attempt to wash the salts off, only results in their being 

 dissolved and absorbed by the bricks, to re-appear as the bricks 

 dry. Rain does not wash them of, but in/o the surface of a 

 building. 



(4) Other causes of production. — Salts of lime are produced 

 by acids and alkalies contained in rain-water, especially that 

 falling in cities. Some twelve years ago an eminent English 

 scientist estimated the quantity of sulphurous acid gas given off 

 by the coal consumed in London at 300,000 tons annually. 

 The carbonic acid gas from the same source must have been 

 many times greater. Tliese two gases have a great affinity for 

 moisture, and are readily taken up by the rain which falls against, 

 and is absorbed by the brick-work, and are the most active agents 

 in producing soluble salts of lime, and so causing it to dissolve to 



