Harukawa. — Toxicity of Colloidal Sulphur. 



223 



The writer calculated the relative toxic effect from the graph 

 according to the formula of Powers (7), and obtained the follow- 

 ing values : 



Colloidal sulphur 0.559 



Lime-sulphur 1 0.293 



Lime-sulphur II 0.103 



EXPLANATION OF THE GRAPH. 



The graph shows the time-concentration curves for the death of gold- 

 fish in colloidal sulphur (C. S. T.). The reciprocal of this curve repre- 

 sents the velocity of fatality (C. S. V.: See Powers, 7); the time to death 

 is arbitrarily divided into 100 in the same sense that that time to go a mile 

 is divided into 60 to give velocity in miles per hour. The velocity of 

 fatality curves of two kinds of colloidal sulphur are also shown for com- 

 parison (L. S. I.) (L. S. II.). 



From the general character of the curves shown by Powers, the least 

 fatal amount of colloidal sulphur probably lies between 0.001 and 0.008 

 per cent. Velocity of fatality curves always turn toward lower concen- 

 trations in the region of least fatal amounts as indicated by the round 

 dots. The steep slope of the curve indicates greater toxicity than the 

 lime sulphur compounds; the least fatal dose is also greater in the case of 

 the lime sulphur compounds. The lime sulphur compounds were used in 

 the hope that fish might be employed to standarize these insect sprays. 



