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



the bell-glass, closed by a cork, which is removed every time, before 

 the bell-glass is raised. 



The stone to be examined is either cut into a dressed cube of an 

 inch on a side, or broken into a fragment of about that form and 

 size ; with either, the result seems to be the same. A sawn cube is 

 always previously digested in ether or chloroform to remove any 

 oil or grease possibly adhering or absorbed during the sawing or 

 handling. All cubes are first dried in a desiccator, over sulphuric 

 acid. Before every weighing, the cube is wrapped tightly iu a 

 doubled sheet of tin-foil of known weight. 



The process consists of the following steps : The cube, on removal 

 from the desiccator, is weighed in its tin wrapper, pressed down 

 into firm contact upon the yielding wet pad of blotting-paper, 

 covered, and there left under the bell-jar until filled by lateral 

 absorption. This usually requires 2 or 3 hours, and is often indi- 

 cated by little drops of water exuding upon the upper surface. 

 The cube is then quickly pressed surface-dry in a piece of filter- 

 paper, instantly wrapped in the tin-foil and weighed. This is 

 repeated to insure constant weight. The cube is then immersed 

 in non-aerated distilled water and put in the vacuum of an air-pump 

 until effervescence ceases, again wiped surface-dry, and weighed in 

 its tin wrapper; this is repeated to constant weight. Finally the 

 cube is weighed in distilled water at determined temperature. 



Four specimens were examined in this way, viz. : — 



A. Granite from the ancient quarry at Syene, selected from a 

 large number of specimens, on account of its fresh appearance. 



B. Gi'anite fi*om the Syene quarry, apparently showing slight 

 decomppsition, by dulled color and lustre, and by some fine ci'acks. 



C. Fresh granite of the Obelisk, obtained in January, 1881, soon 

 after the erection of the Obelisk, and probably derived from chip- 

 pings off the heel of the shaft, done under direction of Commander 

 Gorringe. 



D. Flake of disintegrated granite, removed from surface of the 

 Obelisk in 1885, supplied by the Park Commissioners. 



The trial of these paired specimens yielded the following results: 

 The actual weights obtained, in grams, are given in the table 

 beyond. 



