L. ('. COOLEY. 79-(49) 



unpolished marble below. The color of the stain was an 

 orange yellow, and penetrated the marble to a depth esti- 

 mated to be the fiftieth of a inch. 



. The genera] appearance of the stain was sufficiently 

 unlike ordinary marble discolorations to warrant some 

 examination of its character. Accordingly when the dis- 

 figured column was removed from the monument a por- 

 tion of it was kindly placed in my hands by Mr. Bissell. 

 An analysis failed to betray any mineral constituent of 

 the marble to which the color could be attributed. But 

 on heating the powdered substance, a transient blacken 

 ing plainly suggested the presence of organic matter. 



Further examination was then conducted as follows : 

 A small quantity of the stained marble was mixed with 

 a little soda-lime and placed in a small test-tube which 

 was provided with a narrow delivery tube reaching over 

 into a little tube containing Nessler's reagent, A second 

 tube passed through the cork which permitted a current 

 of air to be blown tli rough the apparatus from a small 

 hand bellows. 



The air tube just mentioned, being closed, a gentle but 

 increasing heat was applied to the mixture. The white 

 powder was blackened, and volatile matter bubbled 

 through the Nessler's reagent and the last portions were 

 finally driven over by the bellows. The Nessler' s reagei 1 1 

 was then found to be decidedly changed, and on standing, 

 i t deposited a yellowish brown precipitate. These results 

 proved the production of ammonia. 



A portion of the unstained marble was then treated in 

 the same way, but it remained white, and the Nessler 1 s 

 was not effected in the slightest degree. Hence the color- 

 ing matter of the stain was an organic substance contain- 

 ing nitrogen. 



No further tests could be made for want of materials ; 

 indeed, the whole quantity of the coloring matter itself 

 at my disposal could not have exceeded a very few milli- 

 grams. 



To what, then, was this coloring due '. Either to some 

 fungus due to atmospheric agency, or to contact with 

 some animal fluid or other nitrogenous liquid. The first 

 of these causes would seem at first glance to be more prob- 

 able, since the decomposition of fungi often yields am- 

 monia. But against this stands the fact that I was unable 



