Study of the New York Obelisk as a Decayed Boulder. 13T 



dissolved in turpentine, was applied at its melting-point (146° P.) 

 by means of a brush, and the stone then warmed again until the 

 excess of paraffin was absorbed beneath the surface. The surface 

 treated, on shaft and plinth, amounted to about 220 square yards, 

 and absorbed 67f pounds of paraffin, to an estimated depth of half 

 an inch or a little more. An equal surface of brownstone would 

 have taken from 40 to 50 pounds, and of brick from TO to 110 

 pounds; so that the great porosity of the weathered coating of the 

 Obelisk is clearly shown. Little difference in the action of different 

 parts of the surface toward the paraffin was noticed, except that the 

 black masses of hornblende were i)articularly absorbent. 



A few months afterwards. Dr. T. Egleston presented views founded 

 on an inspection of the Obelisk and of pieces derived from its decayed 

 surface. Jn these he observed, under the microscope, deep irregular 

 cavities, near the grains of hornblende, empty or partly occupied by 

 that mineral, and crevices containing the green Protococcus referred 

 to by Mr. Dudley. He concluded that disintegration had been long, 

 going on and was still in progress in the interior of the stone, not 

 of chemical but purely physical cause, mainly the repeated expan- 

 sion and contraction produced by the rapid and extreme changes of 

 temperature in this climate. In regard to the waterproofing process 

 applied to the Obelisk, he states:' "The method of applying the 

 present protecting coating seems to have been a fatal mistake. 

 Nothing of any account has been dissolved out of the stone; there 

 is therefore nothing to be replaced. If there had been, paraffin in 

 solution would have been one of the best materials to fill them. 

 Granite is not porous ; there were, therefore, no cavities to be filled. 

 The stone being full of cracks from natural causes, the heat which 

 was used to cause the paraffin to sink into the body of the stone, 

 when applied to the outside, would cause an expansion, which would 

 not be responded to by the interior of the granite, and the cracks 

 already there would increase in size, and pieces would chip off as 

 they did, and new cracks would be formed in the stone, already 

 weakened by long exposure. . . . Even if the surface was entirely 

 waterproofed, the cold of winter and the heat of summer would act 

 below the surface both of the coating and of the stone, causing the 

 coating to break or fissures through it to occur, so as to let in the 

 moisture, and then both causes would operate together as before." 



* Egleston, loc. cit., 81. 

 Ankals N. Y. Acad. Sci., VIII, July, 1893.— 10 



