¹ From the Laboratories of The Rockefeller Institute for Medical Research.

1. While crystalline egg albumin is highly soluble in water at low temperature at the pH of its isoelectric point, it is coagulated by heating. It has long been known that this coagulation can be prevented by adding either acid or alkali, whereby the protein is ionized.

2. It is shown in this paper that salts with trivalent or tetravalent ions, e.g. LaCl₃ or Na₄Fe(CN)₆, are also able to prevent the heat coagulation of albumin at the isoelectric point (i.e. pH 4.8), while salts with a divalent ion, e.g. CaCl₂, BaCl₄, Na₂SO₄, or salts like NaCl, have no such effect.

3. This is in harmony with the fact shown in a preceding paper that salts with trivalent or tetravalent ions can cause the ionization of proteins at its isoelectric point and thus give rise to a membrane potential between micellæ of isoelectric protein and surrounding aqueous solution, while the above mentioned salts with divalent and monovalent ions have apparently no such effect.

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