174 JOURNAL OF CONCHOLOGY, VOL. 9, NO. 6, APRIL, 1899. 



formed, eating away the surface of the shell. The Shell Gallery of 

 the Natural History Museum is, I am assured, excessively dry. This 

 cause is, therefore, excluded. It may be interesting, perhaps, to many 

 collectors to know that in one instance practically the whole of a fine 

 collection of mollusca in Manchester was attacked by a fungoid 

 growth. This arose from the house being extremely damp. Removal 

 to a drier locality and treatment with pure spirit of turpentine restored 

 the shells to their normal condition. The turpentine was rubbed 

 over the surface of the shell, any excess being removed with a dry 

 cloth. The nuisance has never recurred. In no case of this sort has 

 turpentine been known to fail in its action. 



II. — Action of Sulphuric Acid. 



It is well known that the atmosphere of cities contains free sul- 

 phuric acid (in addition to other sulphur compounds) derived from 

 household fires and the burning of coal-gas. This acting over a 

 period of years would slowly eat away the calcium carbonate of the 

 shell, forming calcium sulphate. If this were the explanation, then 

 the whole of the white powdery substance on the surface of the shell 

 would consist of calcium sulphate. Analysis, however, showed that 

 none was present. In order to give some idea of the amount of sul- 

 phur compounds in the air, I append some figures taken from a 

 paper by Dr. G. H. Bailey. 1 



Sulphur Compounds expressed in Parts per Million. 



Owens College, Manchester ... clear breezy weather 



Ditto dull hazy weather, winter months 



Ditto slight fog ditto 



Ditto dense fog ditto 



University College, London ditto Dec. 22, 1890 

 St. Bartholomew's Hospital, London 



dense fog Dec. 22, 1892 



Ditto ditto Dec. 23, 1892 



St. George's Hospital ditto ditto 



Hampstead ditto ditto 



III. — Presence of Salt. 



Shells that had not been soaked in fresh water before being placed 

 in the cabinets would contain salt, not only in the epidermis, but 

 also held mechanically amongst the particles of calcium carbonate 

 It is highly probable that its presence would exert a deleterious 

 influence. 



Chemical tests showed that it was practically absent in the shells 

 examined, a fact that occasioned some surprise. 



1 Some Aspects of Town Air as compared with that of the Country, Manchester Memoirs, 

 ser. 4, vol. 3, for 1803-4, P- 8, 1894. 



