Abstract
Rosenbloom and Gies 1 have shown that many ether soluble substances diffuse from ether through rubber membrane into ether, but oddly various phospholipins do not possess this property.
Together with Boas, 2 I was able to show that various cholesterolesters diffuse from ether through rubber membrane into ether. This is very interesting on account of the high molecular weight of these esters. Cholesterol-stearate with a molecular weight of 652.51 diffuses very readily.
For some time I have been trying to find an ether soluble substance of higher molecular weight than cholesterol-stearate and which could be easily detected in the diffusate. The free dye-acid of iodoeosin fulfilled these requirements. This free dye-acid has been employed by Professor Ehrlich as a very delicate reagent for free alkali in the erythrocytes of man. 3
Iodo-eosin is the potassium salt of tetraiodo-fluorescei'n with the following formula,
As a salt it dissolves in dilute alkalies with red color, but is insoluble in ether or any other organic solvent. The free dye-acid, however, is obtained as a yellow precipitate from the alkaline solution of iodo-eosin by adding hydrochloric acid in excess, and it dissolves readily in ether, or in any other organic solvent, but is insoluble in water. This free dye-acid has the following formula, with a molecular weight of 836.
The dye-acid of iodo-eosin may be made by dissolving ten grammes of iodo-eosin (commercial dye) in one per cent. potassium hydroxide and then adding hydrochloric acid in excess. The dyeacid is precipitated at once, it can then be filtered off and the precipitate washed with hot water till the washings are acid-free. The precipitate after drying is easily soluble in ether, forming a beautiful yellow-colored solution.
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