RED GOLD SOLS ALBERT L. ELDER Syracuse University, Syracuse, New York
THE method for the preparation of a red gold sol described by D. P. Borovskaya [Z. Immunitiits., 82, 178-82 (1934); Chem. Abst., 28, 5485 (1934)l has not received the attention i t deserves. High-school teachers and others wishing to demonstrate the preparation of red gold sols find the Zsigmondy method unsatisfactory. We have used Borovskaya's procedure in classes in colloid and physiological chemistry and for
gold number studies and found it to he reasonably sensitive and also very easy to prepare. To 95 cc. of ordinary distilled water, 1cc. of 1 per cent AuCls solution is added and heated to 90-95OC. About 21/2-5 cc. of 1 per cent sodium citrate are added and the solution is boiled for one and one-half minutes. A light cherry-red sol results. By varying the concentration of citrate and time of boiling, diierent colored sols may he obtained.
