LETHAL GASES 175 



injury and the amount of cyanide that had to be added as a water solution 

 of Ca(CN)2 or KCN in order to produce the same degree of injury. In 

 short, the highly toxic or tissue-killing constituent of the gas was HCN. 

 Scrubbing the gas with water removed some of the HCN, and scrubbing it 

 with NaOH changed the HCN to NaCN and took out most of it. The 

 amount of cyanides in solution ia water necessary to cause the collapse of a 

 small potted tomato plant was very small, 4 to 7 mg. It is interesting to 

 find that it took 20 to 24 times as much illuminating gas that had been 

 thoroughly scrubbed through NaOH solution to give the same amount of 

 killing as was produced by a given amount of unscrubbed gas. Artificial 

 illuminating gas is always scrubbed to remove HCN, and the amount in 

 the gas probably varies considerably from time to time with the thorough- 

 ness of the scrubbing. It is evident that if the scrubbing were thorough 

 enough to remove the last trace of HCN, the killing of trees and shrubs by 

 many small leaks would be avoided. With such thoroughly scrubbed gas 

 it is probable that the killing would result from compounds such as phenol, 

 toluene, xylene, etc. 



Flowing 1 cubic foot and 4 cubic feet of each of the unsaturated gaseous 

 hydrocarbons (ethylene, propylene, butylene, and acetylene) in general 

 produced less injury than the unscrubbed illuminating gas, and the order of 

 sensitiveness of the several plants changes; the tomato was little injured 

 by any of these, even ^vith 4 cubic feet, while the maple was considerably 

 injured, especially by 4 cubic feet of propylene, butylene, and acetylene, 

 the cherry by 4 cubic feet of ethylene, butylene, and acetylene, and the 

 silver bell by acetylene. The tomato, which was the most sensitive to 

 unscrubbed illuminating gas, was among the least sensitive to the un- 

 saturated C-gases, and some plants which were more resistant to un- 

 scrubbed illuminating gas were most injured by the C-gases. 



The results sho^\^l in Table 20 throw out of perspective the significance of 

 the C-gases as toxic factors in illuminating gas because they make up such 

 a small percentage of the gas. The Yonkers gas s. pise contained 3 per cent 

 of ethylene, a fraction of a per cent of propylene, and still less butylene 

 and acetylene. If the Yonkers gas were used as the source of ethylene, one 

 w^ould have to flow 33 cubic feet of it through the pot to get 1 cubic foot of 

 ethylene and many times this volume to get 1 cubic foot of each of the 

 other three unsaturated C-gases. So far as killing roots and stems is con- 

 cerned, the unsaturated C-gases can be disregarded as causes of injury 

 from illuminating gas. 



In order to get gro^vth response from ethylene and perhaps propylene and 

 acetylene, the experiments in Table 20 were run in the wrong way, since all 

 the gas passed through the soil in 30 minutes. Had 1 cubic foot of ethylene 

 or even 1 cubic foot of illuminating gas containing 3 per cent of ethylene 

 been flowed very slowly through the pot during several days or a week, 

 no doubt ethylene responses (leaf epinasty, yellowing of foliage, prolifera- 

 tion of tissues on root and stem) would have appeared. Ethylene would 



