220 American Fisheries Society. 



account and on account of the production of colloidal sulphur. In 

 view of these facts the results obtained in the toxicity study of 

 colloidal sulphur are of some interest to those who are concerned 

 with culture of fish, oysters, etc. The results are, therefore, pre- 

 sented as a preliminary paper. 



METHODS AND MATERIALS. 



The experiments were conducted in a constant temperature 

 tank. The water contained in the tank was kept at a temperature 

 of about 20° C, which did not vary more than 0.5° C. 



The goldfish used for experiments was Carassius carassius L. 

 The criterion by which the writer determined the time of death 

 was cessation of all the movements. A dying fish was carefully 

 watched, and when all the movements (of the eyes, fins, mouth, 

 etc.), ceased, it was touched rather vigorously with a glass rod 

 and watched for two or three minutes more. When this was done, 

 the fish responded with the movements of the mouth, fins, etc., if 

 it was still alive. When there was no response the fish was con- 

 sidered dead. 



Samples of Colloidal Sulphur. — A few methods were tried 

 and discarded. The method of Raffo (5) was adopted with slight 

 modifications. The procedure was essentially the same as described 

 by Rafifo, so that it is considered unnecessary to describe it fully 

 in this paper. A few statements, however, are necessary. When 

 the amorphous soluble sulphur was obtained by precipitating with 

 sodium carbonate, the clear supernatant water was decanted, and 

 an amount of distilled water sufficient to dissolve all the precipitated 

 sulphur was added. The solution was then poured into collodion 

 dialysers and dialysed for at least three days. In most cases the 

 solution was dialysed first with ordinary distilled water for three 

 to five days, and then, with conductivity water for one to five days. 

 During the course of dialysis much of the sulphur dissolved in the 

 solution was precipitated and the concentration was gradually de- 

 creased. It was, therefore, necessary to dialyse for shorter periods 

 to get stronger solutions. 



For this reason the duration of dialysis was not always the 

 same. Because of the instability of the colloidal sulphur solution 

 the writer could not prepare samples of colloidal solution very 

 uniformly. Some of the samples were milky, some were slightly 

 opalescent, while others were perfectly clear and yellowish, show- 

 ing that they were very good colloidal solutions. A good colloidal 



