Aqueous Extracts of Seeds as Agents in the Preparation of Silver Sols.

M\1any methods have been suggested for the preparation of colloidal metals by condensation with the use of organic compounds as stabilizers (1). Among these compounds may be mentioned gum arabic, gelatin, sugar, glycerol, sodium citrate, saponin, barium arabinate, sodium protalbinate, and sodium lysalbinate. Probably colloidal silver has received as much attention as has colloidal gold. Wool-fat has been employed as a stabilizing agent in preparing colloidal silver from organic solutions. KOHLSCHUTTER (2) reduced AgOlH by means of hydrogen. LJUPPO-CRAMER (4) obtained a series of beautifully colored silver sols by the reduction of AgNO3 with hydrochinone in the presence of gelatin. CAREY LEA (3) reduced AgNO3 with ferrous citrate, dissolving the deposit in water and reprecipitating with ammonium nitrate. SVEDBERG (6) observed that a silver plate submerged in water or alcohol produced a silver colloid when illuminated by ultra-violet light or by X-rays. According to TRAUBE-AIENGARINI (7) a certain amount of silver colloid may be produced by boiling silver in water. NORDENSEN (5) showed that silver is oxidized by both water and alcohol and is dissolved as AgOH or some other compound. This silver solution, SVEDBERG has shown, may be reduced by illumination, while TRAUBE-MIENGARINI produced similar results with traces of reducing agents. The dissolution (or oxidation) is accelerated by light, especially ultra-violet light. The method for preparing colloidal silver described in this paper depends upon the ability of aqueous extracts of seeds to reduce AgNO, solutions. A number of methods for preparing colloidal silver have already been mentioned. This is an addition to the list and is highly recommended because of its simplicty of manipulation. It should therefore be of more than passing interest to plant physiologists, botanists, and chemists.