J. Henry on testing Building Materials. 



35 



Carbonate of lime, 54*621 



Carbonate of magnesia, 43*932 



Carbonate of protoxyd of iron, . . *365 



Carbonate of protoxyd of manganese, . . (a trace.) 



Mica, '472 



"Water and loss, *610 



The marble is obtained from a quarry in the southeasterly 

 part of the town of Lee, in the State of Massachusetts, and be- 

 longs to the great deposit of primitive limestone which abounds 

 in that part of the district. It is generally white, with occasional 

 blue veins. The structure is fine-grained. Under the micro- 

 scope it exhibits fine crystals of colorless mica, and occasionally 

 also small particles of bisulphuret of iron. Its specific gravity 

 is 2-8620 ; its weight 178*87 lbs. per cubic foot. It absorbs 103 

 parts of an ounce per cubic inch, and its porosity is great in 

 proportion to its power of resistance to pressure. It sustains 

 23,917 lbs. to the square inch. It not only absorbs water by 

 capillary attraction, but, in common with other marbles, suffers 

 the diffusion of gases to take place through its substance. Dr. 

 Torrey found that hydrogen and other gases, separated from each 

 other by slices of the mineral, diffuse themselves with consider- 

 able rapidity through the partition. 



This marble, soon after the workmen commenced placing it in 

 the walls, exhibited a discoloration of a brownish hue, no trace 

 of which appeared so long as the blocks remained exposed to 

 the air in the stone-cutter's yard. A variety of suggestions and 

 experiments were made in regard to the cause of this remarka- 

 ble phenomenon, and it was finally concluded that it was due to 

 the previous absorption by the marble of water holding in solu- 

 tion a small portion of organic matter, together with the absorp- 

 tion of another portion of water from the mortar. 



To illustrate the process, let us suppose a fine capillary tube, 

 the lower end of it immersed in water, and of which the internal 

 diameter is sufficiently small to allow the liquid to rise to the 

 top, and be exposed to the atmosphere ; evaporation will take 

 place at the upper surface of the column, a new portion of water 

 will be drawn in to supply the loss ; and if this process be con- 

 tinued, any material which may be dissolved in the water, or 

 mechanically mixed with it, will be found deposited at the upper 

 orifice of the tube, or at the point of evaporation. 



If, however, the lower portion of the tube be not furnished 

 with a supply of water, the evaporation at the top will not take 

 place, and the deposition of foreign matter will not be exhibited, 

 even though the tube itself may be filled with water impregna- 

 ted with impurities. The pores of the stones so long as the 

 blocks remain in the yard are in the condition of the tube not 



