400 



Pyrrol. 



This compound was not studied as none could be obtained. 



Hydrogen sulphide. 



This gas occurs in illuminating gas and in solution in waste. It 

 occurs also in the decomposition of organic matter in water and forms 

 an important part of the gas generated in connection with sewage con- 

 tamination. It occurs in small quantity at the bottom of lakes (Birge 

 and Juday, 'ii) but is a very important gas in salt lakes especially 

 those W'ith a thermocline and in thermocline arms of the sea. Marine 

 organisms thus often encounter it, fresh water organisms only in small 

 C[uantities. For experimental purposes it was generated in a Kipp 

 generator of large size by the action of hydrochloric acid on ir6n sul- 

 phide. The generator afforded sufficient pressure to force it through 

 the mixing bottle direct. It was determined with standard iodine. 

 Fifty cc. were drawn from the mixing bottle with a 50 cc. pipette and 

 introduced into an Erlenmeyer flask as quickly as possible and N/ioo 

 iodine quickly added until a brown color was obtained. The mixture 

 was then carefully titrated with N/ioo sodium thiosulphate wdiich 

 had been corrected until it was essentially the equivalent of the iodine, 

 and the amount of thiosulphate used was deducted from the amount 

 of iodine put into the flask. When greater accuracy was desired the 

 determination was repeated, iodine was placed in the flask and the 50 

 cc. of H^S w^'iter added to the excess of iodine beneath the surface 

 and contact with the air essentially prevented. These determinations 

 should be made with great care as slight differences in manipulation 

 gave very variable results in the fish-killing experiments, wath concen- 

 tration which differed only in the error caused by slightly different 

 exposures to the air in rapid manipulation. 



When much diluted it produces nausea, pain in the head, and great 

 general weakness, followed by coma. In concentrated solutions it 

 produces loss of consciousness very quickly. In fishes the symptoms 

 do not appear more quickly than in the case in solutions of other sub- 

 stances. It is more toxic when accompanied by little oxygen. Two cc. 

 per liter are fatal to fishes. Water in a battery jar exposed to the air 

 w4th 4 cc. per liter at the beginning killed fishes in 18-24 hours; mean- 

 while the concentration fell to less than two cc. per liter and the life of 

 the fishes was prolonged by access to the surface. Hardy species of 

 fish live in 1-1.8 cc. per liter without apparent injury. Weigelt found 

 w^eak solutions fatal to tench. 



Fishes are often positive to a weak concentration which would pro- 

 duce death in a few days, but are negative to strong concentrations as 



