Experiments were carried out on the sulfonation of castor oil with concentrated sulfuric acid in an agitated vessel. In order to increase the contact intimacy of the heterogeneous reaction, R. P. M. was varied ranging from 500 to about 2,500 or more. The concentration of sulfuric acid at any time, C was analyzed and the values of ln C/C₀ at each time are plotted against the reaction time. From those plotts, it is found that there are three different stages （or patterns） of reaction; the first stage with fast reaction rate, the second stage of transition from the first to the third and, the third stage with slow reaction rate diffusion controlling. Reaction rate, r, the moles of reacted sulfuric acid per liter per hour is represented as follows;
Frist Stage r=0.225 C （a/Φ）^0.8
Second Stage d（r/C）/dθ=2.23×10^-2(a/Φ)^0.71
Diffusional Stage r=D（a/Φ）C
and （a/Φ） is represented as follows,
（a/Φ）=0.125Ω^0.8N_Re^0.1
where Ω=mole ratio of sulfuric acid vs. castor oil
N_Re=Reynolds number of agitation, n'D_i² ρ_min/μ_mix.