24 



following experiments on the occurrence of copper as 

 well as of iron in various kinds of oysters were undertaken 

 at Professor Herdman's request. The point at issue is 

 not so much the nature of the colouring matter, nor 

 whether it does or does not contain iron, but simply 

 whether the coloured parts of the green oysters contain 

 proportionately such an excess of the metal that the colour 

 can be attributed to its presence. This has not been 

 fomid to be the case. The determination of the copper 

 appeared to be nf some interest, since poisonous effects 

 have often been attributed to its presence, although earlier 

 observers have shown that a small quantity is a normal 

 constituent of the blood of the oyster. 



" Electrolytic methods of analysis were adoped both for 

 the determination of iron and copper; these methods I have 

 already shown (Brit. Assoc. Keports, 1893, p. 726) 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 nifluences traces 

 of organic matter may exert, such as arise when volu- 

 metric or calorimetric methods are employed. In each 

 determination the bodies or gills only of six oysters were 

 carefully washed, dried between filter paper to rem(;ve 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 complete 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 concentrated. The residue was free 



