Structure of Simpler Organic Compounds. 61 



cially, and is decomposed by water in specially constructed 

 apparatus. Acetylene prepared in this manner is largely 

 used as an illuminant. It is a colourless gas, which can 

 be liquefied at 1 under 48 atmospheres pressure. It 

 readily forms addition products with the halogens (see 

 above) by virtue of its unsaturated character, and it can 

 also be reduced by nascent hydrogen into two stages, 

 forming first ethylene, and then ethane. 



CH CH 2 CH 2 CII 3 



+ H 2 = and - - + H 2 = . 



CH CH 2 CH 2 CH 3 



Its most characteristic property is, perhaps, its power 

 of forming so-called acetylides when passed into solutions 

 of certain salts of metals. Thus, when the gas is passed 

 into an ammoniacal solution of cupreous chloride, a red 

 precipitate of copper acetylide, C 2 Cu 2 , is produced, from 

 which acetylene is generated on treatment with hydro- 

 chloric acid. The copper compound readily explodes on 

 percussion, or on heating to 120. 



Isomerism in the Acetylene Series. In addition to 

 compounds containing a triple bond, there also exist in 

 the series of the hydrocarbons of the general formula 

 C n H 2?l _ 2 , compounds containing two double bonds. The 

 former compounds form saturated derivatives by the 

 addition of four halogen atoms to two contiguous carbon 

 atoms, whereas the latter form similar derivatives by 

 addition to more than two carbon atoms. The most 

 interesting member of the series is isoprene, which has 

 the formula CH 2 : C(CH 3 ) CH : CH 2 , which, on a treatment 

 with acids, polymerizes to give a product very similar in 

 its properties to india-rubber. The formula of its tetra- 

 brom-derivative is CH 2 Br . CBr(CH 3 ) - CHBr CH 2 Br that 

 is, the addition of bromine has taken place to no less than 

 four carbon atoms. 



