Concentrated magnetite colloids in kerosene - magnetic fluids - have been synthesized. For stabilization of magnetite nanoparticles, a number of organic acids - lauric, myristic, palmitic, stearic, oleic, behenic and erucic-have been used. Particle size and structure were determined by transmission electron microscopy. Coagulation effect of 15 binary organic mixtures, containing a solvent and a precipitant, in relation to magnetic fluids has been studied in detail. Residual magnetite concentration in above precipitate liquid has been estimated photocolorimetrically. The sets of precipitation curves have been constructed for each stabilizer. A novel parameter for predicting of coagulation effect of precipitants has been suggested. The use of the parameter resulted in fitting of the precipitation curves into a single approximation curve. A method for quantitative determination of medium composition resulting in sedimentation or stability of magnetic fluids can be useful for manufacturing of magnetic elastomers.