36 /. Henry on testing Building Materials. 



supplied at its lower end with water, and consequently no cur- 

 rent takes place through them, and the amount of evaporation is 

 comparatively small ; but when the same blocks are placed in 

 the wall of the building, the absorbed water from the mortar at 

 the interior surface gives us the supply of the liquid necessary 

 to carry the coloring material to the exterior surface, and deposit 

 it at the outer orifices of the pores. 



The cause of the phenomenon being known, a remedy was 

 readily suggested, which consisted in covering the surface of the 

 stone to be imbedded in mortar with a coating of asphaltum. 

 This remedy has apparently proved successful. The discolora- 

 tion is gradually disappearing, and in time will probably be en- 

 tirely imperceptible. 



This marble, with many other specimens, was submitted to 

 the freezing process fifty times in succession. It generally re- 

 mained in the freezing mixture for twenty -four hours, but some- 

 times was frozen twice iii the same day. The quantity of mate- 

 rial lost was '00315 parts of an ounce. On these data Captain 

 Meigs has founded an interesting calculation, which consists in 

 | determining the depth to which the exfoliation extended below 

 the surface as the effect of its having been frozen fifty times. 

 He found this to be very nearly the ten-thousandth part of an 

 inch. Now, if we allow the alternations of freezing and thaw- 

 ing in a year on an average to be fifty times each, which in this 

 latitude, would be a liberal one, it would require ten thousand 

 years for the surface of the marble to be exfoliated to the depth 

 of one inch. This fact may be interesting to the geologist as 

 well as the builder. 



Quite a number of different varieties of marble were experi- 

 mented upon. A full statement of the result of each will be 

 given in the reports of the committees. 



At the meeting of the Association at Cleveland, I made a com- 

 munication on the subject of cohesion. The paper, however, was 

 presented at the last hour ; the facts were not fully stated, and 

 have never been published. I will, therefore, occupy your time 

 in briefly presenting some of the facts I then intended to com- 

 municate, and which I have since verified by further experiments 

 and observations. 



In a series of experiments made some ten years ago, I showed 

 that the attraction for each other of the particles of a substance 

 in a liquid form was as great as that of the same substance in a 

 solid form. Consequently, the distinction between liquidity and 

 solidity does not consist in a difference in the attractive power 

 occasioned directly by the repulsion of heat; but it depends 

 upon the perfect mobility of the atoms, or a lateral cohesion. 

 We may explain this by assuming an incipient crystallization of 

 atoms into molecules, and consider the first effect of heat as that 



