116 RECORDS 



passed through the calcium chloride tubes, where the moisture 

 is extracted, and escapes from the two glass tubes held in the 

 hands at a short distance from the object to be coated. The 

 union of the two gases escaping from the tubes forms ammonium 

 chloride, which settles as an exceedingly fine powder upon the 

 surface of the specimens. The coating thus obtained, when 

 deposited slowly, is of a dead white, which effectually hides all 

 coloration of the surface, and, instead of obliterating the finer 

 modelling, renders the details of the topography with the utmost 

 distinctness. Some surfaces take the coating more readily than 

 others. Fine-grained black limestones and all other rocks that 

 present a velvety surface, take the coating well. Porous rocks 

 are difficult to cover. Specimens which have been handled 

 must be washed with benzene. The coating of the salt is per- 

 fectly harmless, and may readily be removed by water, gentle 

 heating, or the use of a soft brush. Photographs of such coated 

 specimens fulfil more nearly the requirements of the work than 

 do those taken by the ordinary methods. The coating is also 

 of great assistance in the elucidation of the details of small 

 species, as was found to advantage while studying the lobation 

 of the heads of small trilobites. Since the above described 

 method had been devised the speaker had learned of a similar 

 method patented by Professor H. S. Williams. Claim 640,'66o 

 (Off Gaz., 89, p. 2,602) is for "a photographic process consist- 

 ing in the deposition by sublimation from vapor of a temporary 

 film of extreme tenuity on surfaces of the object to be photo- 

 graphed, the film being of a character which removes itself by 

 dissipation, or which may be manually removed without injury 

 to the surface of the object." On the face of it this patent is 

 different from the process described above, although the exact 

 method employed has been guarded as a secret. The cla^im is 

 for a method employing sublimation, which process, as known 

 to chemists and assayers, does not enter in the least degree into 

 the method described by the speaker. 



The paper was discussed by Professors Stevenson and Kemp 

 and Doctors Levison, Julien and White. 



Theodore G. White, 



Secretary. 



