22 OYSTERS AND DISEASE. 



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 colon- 

 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 ioo" 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 (1:2) 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. 



