1. Quantitative data are given on the effect of changes in hydrogen ion concentration and of salt solutions of high concentration on certain immune precipitates obtained at lower salt concentration.
2. Advantage is taken of the shift in reaction equilibrium brought about by the salt in the case of pneumococcus carbohydrate-anti-carbohydrate precipitates to enable the preparation, in a single step from unconcentrated serum, of antibody solutions in which up to 93 per cent of the total nitrogen is immune nitrogen. The method permits successive absorptions of a serum to be made with the same specific precipitate.
3. A modification of Felton's alkaline earth hydroxide dissociation procedure is proposed which yields highly purified antibody with precipitates which have been subjected to several successive salt dissociations.