Study of the New York Obelisk as a Decayed Boulder. 153 



of the paraffin observed ou the cross-section. At that part of the 

 face of the rock which had been subjected to the melted paraffin for 

 one hour, it was found that a layer of twenty-five to thirty-two 

 millimeters (one to one and one-quarter inch) had been saturated.'" 



To facilitate observation of the depth of penetration, the melted 

 paraffin had been previously dyed to a deep red color by alkanet 

 root. But the curious fact was observed that, although the color 

 was apparently held in true solution, it was strained out of the 

 paraffin by the outer layer of decayed rock, about 3 millimeters in 

 thickness, and only uncolored paraffin penetrated below. As the 

 latter was easily distinguished, this result was of no practical im- 

 portance. I presume that it may have been due to a precipitation of 

 the color, as a "lake," by the kaolin or free alumina in the weathered 

 crust of the rock. 



The Report concluded with the following five recommendations 

 by the Committee: — 



" 1. That the comparatively slow penetration of paraffin into the 

 solid granite, after so long an application of heat, confirms the view 

 of the shallowness of the present layer so saturated upon the sur- 

 face of the Obelisk, as accomplished nearly five years ago by the 

 usual quick process. Therefore the experiments of the present 

 Committee lead us to renew the recommendation of local re-treat- 

 ment, in order to insure the safety of the cracked and more badly 

 decayed spots. The absence of the least indications of injury to the 

 stone, after four hours' continuous warming, seems to us to show 

 that the process can be used without danger. . . . 



"2. That the heat should be applied to each spot in the way and 

 with the apparatus already described, at a distance not less than 

 twenty-four inches, in such a way as to keep a thermometer, with 

 its bulb applied to the warmed surface, at a temperature not exceed- 

 ing one hundred and ninety degrees Fahrenheit, and for a period of 

 about two hours. 



"3. That those decayed spots whose small size (three ot- four 

 inches), indistinct sound on tapping, and freedom from visible 

 cracks, indicate the probable shallowness of the decayed or loos- 

 ened flake, shall be then, while still continuously warmed by the 

 stove, repeatedly painted over with melted paraffin, by means of a 

 brush or sponge, for about one-half hour to one hour, until the 

 rejection of the paraffin shows their perfect saturation. 



1 Report, 14. 

 Annals N. Y. Acad. Sci., VIII, July, 1893.— 11 



