222 American Fisheries Society. 



An experiment was carried out with Wackenroder's solution, 

 concentration being about 0.01 per cent. Fishes kept in this solu- 

 tion for 24 hours did not die. 



Control Experiments. — According to Raffo and Mancini, (2), 

 (5), an impurity which is present in an appreciable amount in 

 the colloidal solution of sulphur prepared by Raffo's method is 

 sodium sulphate. This substance could not be completely dialysed 

 away. A solution of colloidal sulphur prepared by Raffo contained 

 about 4.5 per cent of sulphur and 1.5 per cent of sodium sulphate; 

 i. e., of about 6 grams of solids contained in the solution about one- 

 fourth was sodium sulphate. Now, the strongest cencentration that 

 the writer used was about 0.2 per cent. 



The writer considered that the amount of sodium sulphate 

 which might be contained in the writer's solution would not affect 

 the results of experiments. The writer, however, conducted a few 

 experiments with sodium sulphate as control for the experiments 

 with colloidal sulphur solution. 



Experiment i. o.o^ Per Cent Solution of Sodium Sulphate. 

 March 24-25, 1Q22. — Two fishes (one 3.25 grams and the other 

 4.15 grams) were kept in the solution for 24 hours, yet they did not 

 seem to have been affected at all. 



DISCUSSION OF EXPERIMENTS. 



From the rather meager data shown above, the survival time 

 curve and the velocity of fatality curve were drawn. (See the 

 graph.) It is considered that these curves show the relation be- 

 tween concentration and toxicity approximately. From the results 

 of experiments and the curve, the theoretical threshold concen- 

 tration was estimated to be somewhere about 0.008 per cent. 



The straight line part of the velocity of fatality curve is very 

 steep, showing that the toxicity is increased suddenly with a slight 

 rise in concentration. Above about 0.03 per cent the rate of the 

 increase of toxicity becomes smaller. 



The theoretical threshold concentration of sulphur contained in 

 lime-sulphur mixture is 0.009 per cent for lime-sulphur I and 

 0.005 per cent for lime-sulphur II, respectively. 



The velocity of fatality curves of the two kinds (6) of lime- 

 sulphur mixtures are shown partly in the accompanying graph. It 

 will be seen that the straight line part of the velocity curve of col- 

 lodial sulphur is much steeper than those of lime-sulphur mixtures. 



