C^8 



as normal constituents of all Oysters has been shown by 

 the analytical data obtained. 



' The results recorded have been made at Professor 

 Herdman's request, and have proceeded side by side 

 with his investigations. Now that these are completed, 

 a summary of the work from a more purely chemical 

 standpoint may be of interest, especially since the occur- 

 rence of these metals — copper and iron — either from the 

 point of view of the origin of colouration or the cause of 

 poisoning has from time to time been the subject of 

 discussion. 



' The Analytical Method Eviployed. — Electrolytic 

 methods of analysis were adopted both for the determin- 

 ation of iron and copper : these methods, I have already 

 shown,* possess marked advantages for the estimation of 

 minute quantities of metal, especially if derived from 

 organic matter, for they are quite free from any prejudicial 

 influences traces of organic matter may exert, such 

 as arise when volumetric or colorimetric methods are 

 employed. In each determination the bodies or gills only 

 of six or more Oysters were carefully washed, dried 

 between filter paper to remove as much adherent moisture 

 as possible, and then carefully dried in porcelain dishes in 

 the air bath at 100° C. When this drying was as com- 

 plete as possible, the Oysters were heated in the air bath 

 until thoroughly carbonised, the carbon carefully burnt off 

 over the free flame, and the residue finally ignited in a 

 porcelain crucible. Special care was taken to exclude 

 dust during both the drying and the ignition. The ash 

 was then thoroughly extracted with a mixture of 25 c.c. 

 hydrochloric acid and 25 c.c. sulphuric acid (1 : 2) on the 

 water bath, and the resulting solution filtered and 



"Brit. Assoc. Rep., 1893, p. 726. 



