Chrysotile long fibers have been, as descrived in the previous report, synthesized with the addition of magnesium bromide to a raw material mixture of chrysotile composition by dehydration reaction from slurry of the raw material mixture. In the present experiment, pressure variation on the reaction period was measured to be determined the initial and final pressure for obtaining the best yield of the fibers. Based on considerations from the decreasing of partial pressure of water, it was deduced that fibers were formed in such a concentrated slurry that in the final state a near to gel state was attained. An addition of ferrous ions to the slurry exerted a negative effect on the formation of the fibers; a small amount of addition resulted in decreasing in yield, and no fibers were formed in the case of a large amount.
When ferric hydroxide gel as the trivalent ions was added to the slurry, the temperature of formation of fibers was lowered proportionally with the iron content and the degree of this lowering was in accordance with the values calculated from Vegard's low based on Bowen's results. In this case, the trivalent iron was reduced to drivalent by hydrogen evaporated by the dehydration process. This reduced iron might be selectively combined with silica. In the case of the best yield, moreover, the temperature of the formation became lower than the limit of the formation. This temperature drop was seemed to have resulted from the enrichment of the iron at the boundary between the forming fibers and the reacting bulk.