The object of this paper is to find the various errors accompanying the solution of problems of torsion by means of an analogycal method with an electrolytic tank. By the author's experiments, when he can choose a suitable scale for the model and pay attention in selecting the materials of electrods, probe, electrolyte and the apparatus, etc., he can obtain the stresses with errors less than 2% and the torque, with errors less than 1%. By this method, the author treated a shaft with hair cracks and another one with key ways, etc., and the results are shown in this paper.