OXYGEN CONSUMPTION OF OYSTERS 
505 
(1899) and our observations during the summers of 1927 and 1928 have demonstrated 
that all intensely green oysters have high copper content, the latter was used as an 
index of the intensity of pigmentation. 
The copper method used was that of R. Biazzo (1926), which was found to give 
excellent checks on very small amounts of copper, and was therefore suitable for 
determinations on single oysters. Because of slight variations in the method as we 
used it and also because the Italian journals are not always readily obtainable, the 
method is given below in detail: 
Individual oysters were dried to constant weight in crucibles. The dried weight 
used was between 1 and 2 grams. The material was carefully scraped out into a large 
test tube and 5 cubic centimeters concentrated H 2 S0 4 and 1 cubic centimeter of a 
saturated solution potassium chlorate added. After the mixture stopped foa m ing, 
it was gently heated with a microburner and boiled until all the organic matter had 
been oxidized. The process was usually hastened by the addition of 1 or 2 drops of 
hydrogen peroxide. Test tubes were covered with watch glasses to prevent any 
spattering during the combustion. After the solution had cleared, it was emptied 
into a 50-cubic-centimeter beaker and evaporated to dryness on the sand bath to 
render the silica insoluble. The residue was moistened with 5 cubic centimeters of 
IN HC1 followed by 5 cubic centimeters of water, warmed on the sand bath for one- 
half hour, filtered, and the precipitate washed in about 90 cubic centimeters of water. 
The filtrate is evaporated to a volume of 10 cubic centimeters, cooled, and enough 
IN NaOH added to make the solution just alkaline to phenophthalein. Next 1 cubic 
centimeter of glacial acetic acid, 1 cubic centimeter of 10 per cent potassium thio- 
cyanate solution, and 10 drops of pyridine were added. The solution was transferred 
to a 25-cubic-centimeter volumetric flask, 5 cubic centimeters of chloroform added, 
and the volume made up with water. After thorough shaking, the chloroform layer 
was allowed to settle, the aqueous layer removed, and the chloroform compared with 
a standard in the colorimeter. 
Preparation of the standard: Dissolve 0.3926 gram of pure copper sulphate 
(CuS 0 4 .5H 2 0) in water and dilute to 1 liter. One cubic centimeter of this solution 
contains 0.1 milligram copper. Take 1, 2, 3, and 5 cubic centimeters of this solution 
and treat with acetic acid, potassium thiocyanate, pyridine, and chloroform in exactly 
the same manner as the sample. Select the standard which has approximately the 
same intensity of color as the sample. 
Note. — (1) Water distilled in glass must be used throughout, (2) a control must be run on all 
reagents used, (3) the copper compound formed has the formula CuPy 2 (CNS 2 ). 
As a check on the method, 25 normal white oysters were dried to constant weight 
at 100° C., ground, and put through a 60-mesh sieve. This made a homogeneous 
powder, samples of which could be used for copper determinations. One-gram 
samples of this powder were analyzed according to the above method; 1-gram samples 
to which had been added 1 cubic centimeter of a standard copper solution containing 
0.1 milligram of copper were also analyzed. The results are presented in Table 14. 
Table 14. — Control analysis of copper determinations 
Material 
Cu, mg. 
in 1 g. 
Average 
Calcu- 
lated 
Material 
Cu, mg. 
in 1 g. 
Average 
Calcu- 
lated 
Mixed sample ot dried oysters 
0. 1138 
0. 1158 
0. 1142 
0. 1164 
0. 1151 
Same plus 0.1 mg. Cu 
0. 2136 
0. 2120 
0. 2110 
0. 2116 
0. 2121 
0. 2151 
Note. — C ontrol on the reagents gave no color. 
