140 Study of Ihe New York Obelisk as a Decayed Boulder. 



It was apparent that the temperatures recorded by the thermome- 

 ter only indicated the inferior conduction of heat by the layer of 

 cement. Other tests satisfied me that, with a layer of compact 

 stone like granite, the final temperature in each experiment would 

 have risen at least 20° higher than those above observed. 



In order to determine the surface-temperature attained during the 

 heating, the treatment was then applied to a series of dressed cul)es 

 of various building-stones, one inch square, imbedded in square 

 cavities, one inch deep, cut in the surface of the cement, so that 

 the outer faces of the cubes in each group lay in the same plane 

 with the surface of the cement. At the end of the second heating, 

 the bulb of a thermometer was instantly applied to the surface of 

 the cubes and covered with felt to prevent radiation. 



To the final temperatures found, I saw reason to attach no im- 

 portance, as they were evidently much diminished by the rapid 

 radiation, before adjustment of thermometer and felt. So both 

 stove and blast-lamp were then each applied directly to the bulb of 

 a thermometer, at a distance of one inch, shifting the source of heat 

 about in the usual way. It was thus found, on repeated trials, that 

 a temperature approaching 80° to 85° C. (185° F.) was momen- 

 tarily attained. 



From these results we may gather the following as probable 

 conclusions, in regard to the conditions of temperature during the 

 waterproofing treatment of the Obelisk in 1885 : — 



(a). The period of heating by stove or blast-lamp and by the 

 melted paraffin was probably a little longer than in the regular pro- 

 cess, i. e., 2 to 3 minutes (instead of 1). 



(6). The temperature of the melted paraffin, as applied, did not 

 exceed 67° C. (153° F.), and in general was about 63° C. (146° F.). 



