other even when they are stirred to facilitate their mixture they quickly separate when they are subjected to dehydration there inevitably ensues agglomeration of minute particles to preclude this problem this invention causes them to form an emulsion either mechanically or preferably by the forced addition of a surfactant the surfactant may be of an anionic cationic or non ionic type particularly desirable results are obtained when hlb is formulated within the range of 3 to 10 the emulsion formed as described above is a w o type emulsion in which water is dispersed in the form of droplets of about 1 u03bcm in diameter in the organic solvent then this emulsion is deprived of water and the organic solvent by the vaporization method such as by distillation under an atmospheric pressure or under a reduced pressure preferably it is carried out by the vacuum spray method when the heating is continued after the distillation there is obtained a dry powder the powder thus obtained sparingly contains clusters of agglomerating particles it consists mostly of minute particles of diameters not exceeding 1 u03bc the substantial absence of clusters of agglomerating particles is possibly due to the fact that the minute particles of the powder.