the \.\ i ri i.is. 1 25 



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

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

 mariner ; A specimen of Strombus tricornis was soaked in distilled 

 water for a week. A piece about the size of a pea, of a grayish gela- 

 tinous substance was found at the bottom of the glass vessel. Tliis 

 had come from the interior of the shell, and chemical tests showed it 

 tobeorganic matter. The shell had probably been more than twenty 

 years in the Museum. 



This at once furnished the explanation which 1 now bring forward, 

 namely : That the pieces of the animal left in the shell, through in- 

 sufficient 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 carbon- 

 ate into calcium butyrate. 



The reason that land and fresh-water species are not attacked is 

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

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

 sion through lack of such protection. 



The fact that the shells exposed to daily public inspection in the, 

 top cases are less attacked is explained on the hypothesis that the 

 light acts as a deterrent. 1 have also come to the conclusion that the 

 gum used in attaching the shells to the tablets has something to do 

 with the corrosion. The majority of the shells affected in the Na- 

 tional Collection are gummed to tablets. As far as can be ascer- 

 tained, the corrosion has never occurred in private collections where 

 the shells are and always have been loose. The gum ferment-. 

 acetic acid being formed. This eats away the calcium carbonate, 

 forming calcium acetate; this latter substance was found in several 

 of the shells examined, in addition to the calcium butyrate. 



V. Prevention. — In the oase of those shells which are badly 

 affected, nothing can be done, and their instant removal is absolutely 

 • ssential, for if left, they only increase tin- mischief with those just 

 beginning to -how signs of corrosion. I recommend that they lie 

 soaked for twenty-four hours in a solution of corrosive sublimate (1 

 pari in 1,000 water) and then thoroughly dried. 



A- an experiment, all shells should be subjected to such treatment, 

 in the hope that it may prove effectual. It is quite impossible to say 



