]3S Study of the Neio York Obelisk as a Decayed Boulder. 



The crumbling decayed stone from the surface of the Obelisk was 

 very unsatisfactory material from which to determine the condition 

 of the stone beneath, and misled the three observers to quite oppo- 

 site conclusions concerning the decay: Dr. Barnard, to disbelieve 

 in its extent and progress: Mr. Dudley, to connect it with strains 

 produced by the cells of Protococcus : and Dr. Egleston, to attribute 

 it mainly to temperature-variations in our own climate. However, 

 the slight plant-growth was doubtless merely accessory. It will be 

 shown beyond that granite is really porous, and its cavities occupied 

 by a substance, moisture, which must be displaced for the proper 

 introduction of any preservative: that this is too powerful a stone 

 to be injured by gentle warming: and that oscillations of tempera- 

 ture had nothing to do with the sudden disintegration of the surface 

 of the Obelisk in 1882-1885. 



In regard to this mooted and important question — the effect of 

 moderate elevations of temperature on granite, I have next to pre- 

 sent, first, the results of a series of experiments on the application 

 of artificial heat to various building-stones and to the granite of 

 Syene: secondly, some comparative statistics, reduced and tabu- 

 lated, from meteorological reports on thermometric oscillations in 

 Egypt and New York. 



16. Experiments on granite with artificial heat. 



In view of objections taken against the application of heat to 

 granite, as used in the process of waterproofing the Obelisk in 1885, 

 I have made sundry experiments to determine the degree of heat 

 then used and the exact periods of time during which it was applied, 

 repeating exactly the same process with the same apparatus and 

 workmen. 



On testing with a thermometer the melted paraffin compound in 

 the "U. S. pot" used in the process, it was found, if the paraftin 

 was allowed to become entirely fluid, that its temperature rose to 

 70° to 75° C. But when, as always occurred during work, a cake 

 of solid paraffin was kept floating in the liquid, the temperature 

 varied from 59° to 67° C, closely approximating 63° C. (146° F.). 



During the autumn of 1889, the ordinary waterproofing of stone 

 buildings near New York City was carefully studied. On a cold 

 day, at Orange, N. J., I carefully watched the application of the 

 process to surfaces of Nova Scotia sandstone, in a state of incipient 

 decay, to ascertain the periods during which the stone surfaces 



