The velocity of 10 MHz sound waves in solutions of lithium, calcium and barium in ammonia are presented. The sound velocity in the lithium and calcium solutions exhibits a minimum which had not previously been detected. This minimum is a function of the metal concentration and of the temperature. Previous investigations of the sound velocity in potassium and sodium ammonia solutions did not reveal the presence of such a minimum. It is postulated that the minimum is an indication of compound formation in the solutions. Calculations of the sound velocity for the lithium–ammonia solutions are presented using the scheme of Schroeder and Thompson. Data on the saturation curve of the lithium–ammonia solutions is also presented.

SINCEthe discovery that fluorine is a causal factor of the dental defect known as mottled enamel on teeth, the literature of analytical chemistry has abounded with papers describing methods for its determination in small amountsthat is, up to a few parts per million. More recently the increased use of fluorides as insecticides has stimulated interest in' such methods and, since the U. S. Food and Drug

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THEproblem of determining sodium in aluminum is not a new one. As early as 1859, Sainte-Claire Deville (24) developed a leaching method for the determination of sodium. He converted the aluminum to nitrate, ignited at low temperature, and leached the alkalies with water. This method has been used or modified by Diehl (8), Richards (28), Hunt, Langley, and Hall (14), Moissan (18), Jean (15), Seligman and Willott (26), Kohn-Abrest (16), Belasio (8), Bhattacharyya (5), Pattison (22), Villavecchia (27), and Bertiaux (4)• Handy (18) dissolved aluminum in hydrochloric acid and nitric acid, ignited gently, and applied the J. Lawrence Smith method to the oxides formed. Allen (1) dissolved aluminum in hydrochloric acid, made an ammonium hydroxide separation, and deter-

A REVIEW of the literature shows that analytical chemists have been more or less dissatisfied with the status of procedures for the determination of silicon in aluminum and aluminum alloys. The main basis of uncer-