An interesting item in Thomasset's patent on the use of nickel (SS) is the statement of the requirement of low oil absorption of the blue for maximum alkali stability. This would be indicative of a decreased total surface for the pigment particles, which would be accompanied by decreased powers of adsorption.To conclude, the constitution of the iron blues is still in doubt.Most of the early work was carried on and interpreted from a single viewpoint only. Because of the complexity of the systems involved, simultaneous attacks ,on the problem from different angles are required, such as have been initiated recently by Weiser and others. Aging studies under suitable conditions, accompanied by chemical, colloidal, x-ray work,'etc., would aid in resolving the controversies over this subject.The nickel and alkali stability problems are tied up with the general problem of constitution, and further elucidation of the latter will aid in explaining the facts associated with the former.
ACKNOWLEDGMENTThe suggestions, advice, and criticism received from David Davidson and Joseph Greenspan, of the Department of Chemistry, Brooklyn College, are gratefully acknowledged.