268 



BOTANICAL GAZETTE 



[OCTOBER 



Components 



Coal gas 



Water gas 



Oil gas 



Illuminants 



Heating gases: 



Methane 



Hydrogen 



Carbon monoxid . 

 Impurities : 



Nitrogen 



Carbon dioxid . . . 



5° 



34-5 



49° 



7-2 



3-2 

 1. 1 



16.6 



19.8 

 32.1 

 26.1 



2.4 

 3° 



45 -° 



35-8 

 14.6 



Candle power . 



17-5 



25.0 



65.0 



These are average numbers, and considerable variations from these propor- 

 tions are often met with. The illuminants are unsaturated hydrocarbons, such 

 as ethylene and acetylene, and the value of the gas for illuminating purposes 

 depends on the amount of these particular components. 



The illuminating gas used in our experiments was water gas of the 

 People's Gas Light and Coke Company, drawn from a tap in the 

 Botanical Laboratory. In numerous analyses of samples of this gas 

 (see Hempel, p. 282) absolute alcohol absorbed 0.2-0.6 per cent., 

 and fuming sulfuric acid n -14 per cent. Absolute alcohol absorbs 

 the so-called hydrocarbon vapors (mostly benzene); and fuming 

 sulfuric acid the heavy hydrocarbons, including acetylene, ethylene, 

 and their higher homologues. Bromin is often used as an absorbent 

 of ethylene. Besides ethylene, however, it absorbs several other con- 

 stituents of illuminating gas. In a number of analyses this reagent 

 absorbed 9-13 per cent. A more definite determination of ethylene 

 will be given in the experimental portion. 



At first the illuminating gas used was washed through 33 per cent, 

 potassium hydrate to absorb any traces of sulfur dioxid and hydrogen 

 sulfid it might contain. This was found not to modify the toxicity, 

 and hence the unwashed gas was used thereafter. The methods of 

 deriving and purifying the other constituents (of illuminating gas) 

 worked with will be described in the later paper, which gives their 

 effects. 



3. Experimental 



ILLUMINATING GAS 



As a later paper will deal fully with the effects and toxic limits 

 of the constituents other than ethylene, we need make only a general 

 statement concerning them here. A number of experiments were run 



