In the dipositive state, the lanthanonst are chemically similar to the alkaline earth elements and, like the latter, give reciprocal replacement with alkali metal amalgams. This is best studied by the use of sodium amalgam and concentrated solutions of the lanthanon(II1) acetates. 1-6 Acetates of all of the elements of the yttrium and cerium groups are capable of some metal exchange with sodium amalgam, but the samarium, europium, and ytterbium compounds react most readily, presumably because of the ease of reduction to the dipositive state with these materials. Amalgams of those lanthanons which do not yield dipositive ions form much less readily. In the cerium group, except for samarium and europium, metal exchange with sodium amalgam decreases rapidly from lanthanum to gadolinium. In the yttrium group, the decrease is so pronounced that the neighbors of ytterbium give essen-* The Dyson Perrins Laboratory, Oxford, England.t Lindsay Chemical Company, West Chicago, Ill.

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