LETHAL GASES 179 



be used. Several days after the leak has been stopped one can judge rather 

 accurately from the behavior of the various kinds of plants in the green- 

 house whether ethylene has been present. Some greenhouse men show 

 great accuracy in observing and describing unusual responses in the plants 

 they are gro^^^ng. With accurate descriptions of the responses, one can 

 judge fairly accurately whether ethylene was involved long after the injury 

 has occurred. It is more difficult to determine gas injury to trees or shrubs 

 outside, especially when the plant is killed quickly. No physiological 

 responses of ethylene appear. One can locate the leak and observe the 

 degree of injury to plants at various distances from the leak. On the out- 

 skirts of the area of injury he may find ethylene responses in plants that 

 are not killed. One should also observe various plants within the zone of 

 injury for the red color in the roots due to phenol. 



Samples of soil should be taken from different depths and from various 

 distances from the leak and test plants exposed to the soil samples under 

 bell jars to detect the presence of ethylene. The samples should be taken 

 with as little stirrmg as possible and kept tightly sealed until ready to be 

 placed under the bell jars for the test. The author has often obtamed 

 ethylene responses from such tests, which of course show that gas has been 

 present. Hitchcock, Crocker, and Zimmerman did not find chemical tests of 

 soils for the presence of various constituents of gas of very much value in 

 diagnosing gas leaks. Among these were treating soil extracts with bromine 

 water to detect ethylene, etc., reactions for phenol and cyanides in soil 

 extracts. Drip oils do often discolor the soil in the immediate region of the 

 leak. 



Leaks are more likely to develop in the winter mth freezing and thawing 

 of the ground. If there is a frozen soil crust after a big leak develops, the 

 gas is likely to move for considerable distances under the crust in sufficient 

 amounts to cause injury over a sizable area. If the roots are killed in the 

 early spring the foliage may open out, but the leaves remain very small and 

 die later. If the roots are killed in midsummer the full-sized leaves die and 

 dry up. 



Injury from Natural Gas 



With one knouTi exception natural gases do not contain ethylene or 

 other similar growth-modifying gases and, in the one exception claimed to 

 date, the percentage of ethylene is extremely low.^ Natural gases ^- ^^ 

 also contain no HCN, phenol, toluene, xylene, etc. Natural gases have 

 methane (CH4) as the main constituent. In some, methane is the sole 

 combustible constituent. Others contain in addition the higher homologs 

 of methane — ethane, propane, and butane as gases, and vapors of pen- 

 tane, hexane, heptane, and octane. Natural gases from some fields contain 

 hydrogen sulphide and organic sulphur compounds. In some of these the 

 hydrogen sulphide runs as high as 15 per cent. Hydrogen sulphide, if 

 present, is supposed to be completely scrubbed out before the gas is de- 



