BYNE : THE CORROSION OF SHELLS IN CABINETS. 175 



Mrs. Kenyon, in the paper above mentioned, says : — " I had the 

 opportunity of visiting a collection on which the near vicinity of the 

 sea had the effect of partially destroying the enamel of the dorsal 

 surface by streaks or clouds of a whitish or lime-like substance, the 

 saline particles held in solution in the atmosphere evidently exerting 

 a corroding effect in this instance." It must be pointed out that so 

 far as we at present know, the gases which constitute our atmosphere 

 (oxygen, nitrogen, argon, etc.) have no power to dissolve saline par- 

 ticles. Solid particles of salt are, however, held mechanically in minute 

 amounts. 



As the shells under consideration were not near the sea, we may 

 dismiss this cause from our further consideration. 



IV. — Action of an Acid Substance. 



After carefully considering all the facts in my possession, I have 

 come to the conclusion that the corrosion is due to the action of 

 butyric acid. 



Upon opening the box of shells sent me by Mr. E. A. Smith, I at 

 once noticed a pungent vinegar-like odour, which pervaded the 

 fingers and everything that came in contact with them. This pointed 

 to the presence of acids of the acetic series. Analysis showed that 

 every shell contained butyric acid as calcium butyrate. A few con- 

 tained calcium acetate. Butyric acid is a product of the fermentation 

 of animal matter, and its original source was found in the following 

 manner : — A specimen of Strombns_ tricornis was soaked in distilled 

 water for a week. A piece, about the size of a pea, of a greyish 

 gelatinous substance was found at the bottom of the glass vessel. 

 This had come from the interior of the shell, and chemical tests 

 showed it to be organic matter. The shell had probably been more 

 than twenty years in the Museum. 



This at once furnished the explanation which I now bring forward, 

 namely : — That the pieces of the animal left in the shell through 

 insufficient cleaning or otherwise, ferment, setting free butyric acid. 

 This substance is extremely volatile, and pervades the whole of the 

 drawers and cabinets. The amount present can only be extremely 

 small, but acting as it does for so many years, it slowly eats away the 

 surface to a considerable extent, converting the calcium carbonate 

 into calcium butyrate. 



The reason that land and freshwater species are not attacked is 

 that their epidermis acts, so to speak, as a coat of mail. Hence, 

 highly-polished species of Cyprcea, etc., are the most liable to corro- 

 sion through lack of such protection, 



