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Method

zinc, sample and solution

METHOD.

The method of analysis followed is that advised by the U. S. Depart ment of Agriculture, Bureau of Chemistry, Bulletin No. 107 (revised), with slight modifications, as tin was not sought. The sample was incinerated in a muffle at a low red heat, not high enough to fuse the chlorides. After solution of the ash in HCl and evaporation to dryness, sulphides were precipitated in a hydrochloric-acid solution. They were then dissolved in when copper and lead, if any, were determined electrolytically in the nitric-acid solution. Iron and phosphoric acid were separated from zinc in the filtrate from the sulphides by the basic-acetate method, when the zinc was precipitated as a sulphide in an acetic-acid solution and weighed as ZnO. If this zinc oxide was found to be impure it was dissolved in hydrochloric acid, filtered, and the filtrate was boiled with an excess of NaOH in platinum, any precipitate filtered off, and the zinc reprecipitated with and again weighed as ZnO.

Iron was estimated in a separate sample, usually 2 grams, by titra tion with permanganate. Manganese was also estimated in a separate

sample, by the colorimetric method, and both, as tabulated below, are calculated to amounts contained in 20 grams of the dry sample. The weights, etc., are given in grams.

The constant occurrence of both copper and iron in the analyses is to be expected, but the large amounts of copper in some and its variability, even in individuals of the same species, is to be noted. Zinc is present in all the specimens analyzed except the crayfish blood, and as the sample was exhausted in the first analysis this could not be tested further. Since the Tortugas Islands are far removed from any possible contamination of the sea-water, zinc must be considered as a normal constituent of these forms. Manganese is present in all the specimens analyzed, but varies considerably. The most remarkable occurrence, however, is that of lead in the liver of Fasciolaria gigantea in quantity just sufficient to weigh, in a 20-gram sample of dried liver, but quite enough to yield good qualitative tests.