The theory of the flotation process is based upon the physical chemistry, and relations between mineral particles and surrounding medium are important to solve the problem. The size of mineral particles in flotation has not yet been fully investigated, especially in connection with theoretical considerations.
In this paper author describes an investigation on the sizes of mineral particles to be treated in flotation; particularly on floatability of the mixed size, and influence of minute particles on coarse particles and vice versa. Author experimented with both, film flotation apparatus and froth flotation machine, and for convenience, used some coal as a sample, but furthur he is ready to try on some sulphide minerals.
From the result of experiments the following items are summarised:
1. The maximum size of a floatable coal particle by film flotation is about 1 cm³; this coincides with the calculated value.
2. Floatability by film flotation rises up to 100%with coarseness of particles till the maximum size above mentioned is arrived, but descends with fineness of particles.
3. Ash reduction, however, is imperfect when the size of particles becomes coarser.
4. By froth flotation, most favorable size, from both recovery and quality, is classed under the figures, 65, 150, 48, 100 and 200 mesh (order of favorability).
Too fine (-200) or too coarse (+28) particle is unfavorable.
5. The considerably favorable mixtures are as follows:(100+150), (150+200), (65+150), (48+65), (48+100), (65+100), (65+200), (35+100), (100+200), (35+48), (35+65), (35+150), being the range of sizes 35-200 mesh.
6. The coarser and the finer are affected by each other; generally speaking the finer acts on the coarser so badly as to make it less floatable, but the coarser on th finer to break the flocculent cloud in the pulp and make more floatable.
In particular case, however, less floatable and coarse particles are promoted to float by the most favorably conditioned finer-particles.
7. Some practical possibilities in flotation can be deduced from the results; for example, the length of the machine should be determined by not only the capacity required but also the time of duration for completion of floating, which is characterized by the nature of particles; or close sizing is to be required or not; etc, etc Here, however, these subjects are not concluded, and remained in the next cpportunity.

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