Gelatin protective effect

Kermack and Wright Biochem. J. XVII. 635,1923) have shown that gelatine at a of 4 T exerts but little protective power on a negative gum benzoin sol, acid gelatine precipitates the colloid in small concentrations whilst alkaline gelatine protects it. Similar observations have been made by Zsigmondy on the effect of casein on gold, but its exact isoelectric point was not established. 

The colloidal nature of soap solutions is manifested by the protective action on gold solutions. The gold number of sodium oleate lies between 0.5 and 2. The protective effect is therefore about as great as that of gum arabic, and much smaller than that of gelatin. The protective effect of sodium stearate increases with the temperature. 

The effect of temperature on the corrosion of zinc in water It is found that the temperature has a marked effect on the rate at which zinc corrodes in water. The corrosion rate in distilled water reaches a maximum in the temperature range 65-75°C. This variation in the corrosion rate with temperature is attributed to changes in the nature of the protective film. At lower temperatures the film is found to be very adherent and gelatinous, while at temperatures around 70°C it becomes distinctly granular in character and much less adherent. Above 75°C it again tends to become more adherent and assumes a very compact and dense form. It is believed that the granular coating formed at temperatures around 70°C is more porous... 

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