30 



/. Henry on testing Building Materials, 



Art. V.— On the Mode of testing Building Materials, and an ac- 

 count of the Marble used in the Extension of the United States 

 Capitol ; by Professor Joseph Henry, Secretary of the Smith- 

 sonian Institution.* 



A commission was appointed by the President of the United 

 States, in November, 1851, to examine the marbles which were 

 offered, for the extension of the United States Capitol, which 

 consisted of General Totten, A. J. Downing, the Commissioner 

 of Patents, the architect, and myself. Another commission was 

 subsequently appointed, in the early part of the year 1854, to 

 repeat and extend some of the experiments, — the members of 

 which were General Totten, Professor Bache, and myself. 



A part of the results of the first commission were given in a 

 report to the Secretary of the Interior, and a detailed account 

 of the whole of the investigations of these committees will ulti- 

 mately be given in full in a report to Congress, and I propose 

 here merely to present some of the facts of general interest, or 

 which may be of importance to those engaged in similar re- 

 searches. 



Although the art of building has been practised from the earli- 

 est times, and constant demands have been made, in every age, 

 for the means of determining the best materials, yet the process 

 of ascertaining the strength and durability of stone appears to 

 have received but little definite scientific attention, and the com- 

 mission, who have never before made this subject a special object 

 of study, have been surprised with unforeseen difficulties at every 

 step of their progress, and have come to the conclusion that the 

 processes usually employed for solving these questions are still 

 in a very unsatisfactory state. 



It should be recollected, that the stone in the building is to 

 be exposed for centuries, and that the conclusions desired are to 

 be drawn from results produced in the course of a few weeks. 

 Besides this, in the present state of science, we do not know all 

 the actions to which the materials are subjected in nature, nor 

 can we fully estimate the amount of those which are known. 



The solvent power of water, which even attacks glass, must 

 in time produce an appreciable effect on the most solid material, 

 particularly where it contains, as the water of the atmosphere 

 always does, carbonic acid in solution. The attrition of siliceous 

 dusts, when blown against a building, or washed down its sides 

 by rain, is evidently operative in wearing away the surface, 

 though the evanescent portion removed at each time may not be 

 indicated by the nicest balance. An examination of the basin 



* From the Proceedings of the American Association for the Advancement of 

 Science, held at Providence, R. I., August, 1855. New York : 1856. 



