The Effect of Addition of Colloids on the Coagulation of Latex

1. A known proportion of colloid was added to dilute, dialyzed latex (rubber content 3.5 per cent) to determine the effect of colloids on the coagulation of latex. Various proportions of 0.2 N acids were added; the mixtures were then left for 24 hours. The relations between the state of coagulation of latex and the proportion of acid are shown graphically. 2. The coagulation curves of acetic, hydrochloric, sulfuric, and nitric acids show that latex is coagulated by a definite quantity of acid, above which proportion the coagulation disappears and then reappears by further addition of acid. The first coagulation is apparently governed by the p H value of the dispersed medium, and the charge on the surface of the rubber particles is opposite to that of rubber dispersed in an alkaline medium. The second coagulation is governed by the concentration of cations. 3. Gum arabic, casein, saponin, gum tragacanth, glue, “funori,” or hemoglobin were added to latex and coagulation obtained by the addition of 0.2 N acetic acid or hydrochloric acid. Each gave the characteristic curve of a protective colloid; dextrin, however, had no influence on the coagulation curve. 4. The influence of the colloids on the coagulation curve is of particular interest in studying further the properties of colloids and rubber particles, and this will be discussed in detail in connection with further investigations.