[en] The technology of the magnetic colloid preparation is described for use in fine adjustment operations involved in output of secondary particle channels on accelerators. A modified Elmore colloid preparation method is proposed eliminating magnetic deposit peptization with hydrochloric acid that is liable to cause more free Cl^- ions to be formed promoting coagulation. The most suitable colloid preparation inhibitor has been found to be dodecylamine-(1-aminododecane) CH₃(CH₂)₁₀CH₂xNH₂. The magnetic deposit composition for the novel colloid is prepared in the same manner as that for Elmore colloid