After a preliminary survey with the electron microscope of various preparations of colloidal gold, a study was made of the process of nucleation and growth in gold colloids. It was shown that nucleating agents may be identified with reducing agents which form a mixed polymer with chlorauric ion before the reduction to the nucleus takes place. It was also shown that the law of growth is exponential. The average size, the deviation from the average size and the character of the particle size distribution curve are determined by the amount of gold, the nucleation process and the law of growth.Colloidal gold may be considered as a typical hydrophobic colloid with particle size falling below the resolution limit of the optical microscope. With the development of the electron microscope which has s resolution permitting the examination of the individual colloidal particles 1 it was natural to make an extensive study of the shape, mean size and size distribution of the various preparations of colloidal gold and determine the factors that govern these properties. Previous work on the subject was limited to one or two preparations.4 l1 Hauser and Lynn, Ex9eriments in Colloid Chemistry (McGraw Hill, 1g40), p. 18.

An electron microscope study has been made of the process of reduction of gold chloride to colloidal gold. A method was found of producing gold of uniform size in the diameter range of 200-1500 A. It was found that the particle size distribution curve of colloidal gold preparations is not an error curve but is determined by the kinetics of the process: the nucleation stage and the growth stage. A theory of nucleation is proposed based on the formation of auric ion-organic reducing agent complex which on attaining proper size decomposes to form a gold nucleus. This theory is shown to be in agreement with experiment. The exponential law of growth of the colloidal gold was also established. 4

No abstract

No abstract

No abstract