25 



from both copper and iron. The acid solution obtained 

 was electrol3'sed 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 am- 

 monium hydrate, &c., acidifying with a few drops of 

 oxalic acid solution, and boiling with ammonium oxalate. 

 Four 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 (0'000'2 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 following table gives the results obtained, the iron 

 being expressed in milligrammes per six oysters or gills 

 of six oysters in each case, so that the weights given 

 express the figures actually found. 



T. — Determination of Iron. 



"From these figures it is evident that there is not an 

 excessive quantity of iron in the gills of the green oysters, 

 the proportion of iron in the gills as compared with the 



