350 WRITINGS OF JOSEPH HENRY. [1855 



The commission considers these determinations, and par- 

 ticularly that of the resistance to crushing, — tests of much 

 importance, as indicating the cohesive force of the particles 

 of the stone, and its capacity to resist most of the influences 

 before mentioned. 



The amount of water absorbed may be regarded as a 

 measure of the antagonistic force to cohesion, which tends, 

 in the expansion of freezing, to disintegrate the surface. In 

 considering however the indication of this test, care must be 

 taken to make the comparison between marbles of nearly the 

 same texture, because a coarsely crystallized stone may appar- 

 ently absorb a small quantity of water, while in reality the 

 cement which unites the crystals of the same stone may 

 absorb a much larger quantity. That this may be so was 

 clearly established in the experiments with the coarsely 

 crystallized marbles examined by the commission. When 

 these were submitted to a liquid which slightly tinged the 

 stone, the coloration was more intense around the margin of 

 each crystal, indicating a greater amount of absorption in 

 these portions of the surface. 



The marble chosen for the Capitol is a dolomite, or in other 

 words, is composed of carbonate of lime and magnesia in 

 nearly atomic proportions. It was analyzed by Dr. John 

 Torrey, of New York, and Dr. Frederick A. Genth, of Phil- 

 adelphia. According to the analysis of the former it con- 

 sists, in hundredth parts, of — 



Carbonate of lime ...... 54-621 



Carbonate of magnesia 43-932 



Carbonate of protoxide of iron .... -365 



Carbonate of protoxide of manganese . . . (a trace) 



Mica -472 



Water and loss -610 



The marble is obtained from a quarry in the south-easterly 

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

 belongs 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 microscope it exhibits fine crystals of colorless mica. 



