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A simple, rapid, and inexpensive titration method with gold sol was developed which measured the fraction of hydrophilic gum arabic that was free in the aqueous (continuous) phase and thus indirectly, the fraction of the gum which coated the oil droplets, thereby fulfilling its intended stabilizing function. For a series of gum arabic-stabilized emulsions of varying particle sizes, the gold number measured for fresh emulsions related directly to the long term storage stability of these emulsions at high dilution.

With the application of ultrasonic energy a colloidal gold may be easily prepared with a particle diameter of less than 10 nm and suitable for use as an immunological marker for TEM-studies. This new approach replaces the use of phosphorus, traditionally used for producing gold sols of the smallest diameter.

(1910). COLLOIDAL GOLD AND “PURPLE OF CASSIUS.”. Transactions of the Royal Society of South Africa: Vol. 2, No. 1, pp. 203-204.

Occasional allusion is made to the role of “protective colloids” in physiological processes. Commonly these are evaluated according to their “gold number”, on which basis gelatins are conceded to be particularly powerful protective colloids (gold number 0.005 to 0.01).1In connection with a series of digestion experiments we have had an opportunity to observe the influence of peptic digestion on the protective power of gelatin, as measured by gold number. These included both in vitro peptic digestion experiments, and observations upon gastric samples removed periodically from human subjects following gelatin meals.The beaker experiments indicated that digestion with pepsin has no influence on the protective colloid value of gelatin. That digestion actually occurred was determined by precipitation with trichloracetic acid and subsequent determination of non-precipitable nitrogen, as well as by observing the gradual loss of viscosity and power to form gels. The digestion of a 10 per cent gelatin solution fur...

IN three previous notes in NATURE1 it has been pointed out that the diamagnetism of graphite, antimony, and bismuth decreases with particle size. This was most striking in graphite and less in antimony and bismuth. In a later communication on the same subject2 I adopted two methods of colloidalisation of bismuth—Bredig's method and mechanical colloidalisation. In Bredig's method I obtained an abnormally low value, due to the powder containing a mixture of oxide and the metal, as was pointed out by me. In the case of bismuth, S. S. Bhatnagar3 contends that he obtains a large amount of oxide by mechanically colloidalising bismuth, and part of the decrease of diamagnetism that I obtained by that method is also due to oxidation.

Colloidal silver and gold have been formed by irradiation of AgClO4 and HAuCl4 solutions with 253.7 nm light in the presence of protective agents such as sodium dodecylsulphate, sodium alginate and colloidal silica. Absorption maxima of colloidal silver and gold have been observed at 390–420 and 540–560 nm, respectively. Colloidal metals have been purified by dialysis and their amounts analysed quantitatively. The quantum yields of metal deposition are 0.053–0.15 for colloidal silver and 0.030–0.039 for colloidal gold. The quantum yield is increased several times by the use of protective agents, with the exception of a AgClO4–sodium alginate solution.

SOME time ago, in a communication from this Department1, it was shown that a steadily increasing exposure to X-radiation produced alternate increases and decreases in the electrokinetic potential of certain colloid particles. The colloid used at the time (a dilution of 'Aquadag' in water) is peculiarly stable, and at no stage were there any signs of coagulation. It was thought possible that with a more sensitive colloid the decrease in potential at the minima of the curve might be sufficient to bring the colloid to its flocculation point, and at my suggestion Dr. Liebmann and Mr. Jones have been working with certain pure gold sols.