22 
OVSTMRS AND DISFASE. 
especially if derived from ort^anic matter, for they are quite free from any prejudicial 
influences traces of organic matter may exert, such as arise when volumetric or colori- 
metric 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 complete as possible, the oysters were 
heated in the air-bath until thoroughly carbonized, 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 (i : 2) on the water-bath, and the resulting solution filtered and 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 grms., being employed as the cathode. The wire was determined in 
the residual solution, after neutralization with ammonium 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 electro- 
lysed, 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 
(0.0002 grm. 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. 
I. — Determination of the Iron. 
The following table* gives the results obtained, the quantities of iron found in 
green French as compared with white American oysters, three sets of gills being 
analyzed in each case. The figures show conclusively that there is more and not less 
iron in the gills of the white American oysters than in the French, and this irrespective 
of the basis on which the result is calculated. The ash is undoubtedly the most reliable 
factor to calculate on, provided the oysters are carefully washed before drying, which is 
always done : the result per set of gills (or oyster) is most in accord with this, and has 
the advantage of being an easy and in many respects useful basis. 
* We are indebted for all the Tables in this section to the careful work of our colleague at Liverpool, Dr. 
C. A. Kohn. and we take this opportunity of thanking him most cordially for his kindness in helping us. 
