SEA-FISHERIES LABORATORY. 137 



concentrated. The residue was free from both copper 

 and iron. The acid solution obtained was electrolysed 

 for copper with the usual precautions, a spiral of fine 

 platinum wire weighing about 5 grme. being employed as 

 the cathode. The iron was determined in the residual 

 solution, after neutralisation with ammonium hydrate, &c, 

 acidifying with a few drops of oxalic acid solution, and 

 boiling with ammonium oxalate : 4 grme. of the oxalate 

 were added in each case, the precipitated calcium oxalate 

 (which is quite free from iron) filtered off and thoroughly 

 washed and the resulting solution electrolysed, the metallic 

 iron being also deposited on a spiral of platinum wire. A 

 blank experiment with all the reagents employed was 

 made, and the amount of metal found (0*002 grme. iron) 

 deducted in each case. Also the deposited metal, both 

 iron and copper, was dissolved off the electrode by acid, 

 the solution obtained tested by the ordinary reagents and 

 the spiral re-weighed, as a check upon the determinations, 

 since the quantities found were extremely small. 



' The Green Colour of French Oysters, " Hultres de 

 Marennes" and the Presence of Iron in Oysters. — The early 

 observations of Dumas (1841) and of Berthelot (1855) 

 showed that the green colour of "Huitres de Marennes " is 

 not due to chlorophyll, and that although every Oyster 

 contains a certain very small amount of copper in its 

 blood in the form of " hsemocyanin," as determined by 

 Fredericq, the green colour of the French cultivated 

 Oyster is not due to this metal. Ray Lankester* in 1886 

 confirmed the latter statement, and states in his investi- 

 gation on the histological condition of the colour that 

 there is neither copper nor iron in the refractory blue 

 pigment " rnarennin " of the coloured portions of the 



* Quart. Journ. Micros. Sci., 1886, 26, 71. 



