8o 4 THE POPULAR SCIENCE MONTHLY. 



ethylene — which is the chief light-giving constituent of illumi- 

 nating gas. Ethylene, when brought into contact with sulphuric 

 acid, forms a liquid combination, and this when treated with po- 

 tassium hydrate is converted into alcohol. Having thus built up 

 from its elements a substance formerly known only as a product 

 of fermentation, we may proceed at once to decompose it again 

 into its elements. We can easily regain the carbon which it con- 

 tains, by heating alcohol with sulphuric acid, which again con- 

 verts it into ethylene ; and this gas, when mixed with chlorine gas 

 and lighted, burns away, leaving carbon, which as a dense black 

 smoke fills the vessel. 



An event very encouraging and helpful to synthetical investi- 

 gations was the artificial preparation of urea, a product of secre- 

 tion in animal bodies, resulting from the decay of muscle, and one 

 of the most important substances in animal exchange of matter. 

 When Woehler, in 1828, found out that, by a chemical process, it 

 can be composed with all its physical and chemical properties, this 

 event gave a tremendous shock to the foundations of the doctrine 

 formerly believed, that a " vital power " governed the functions of 

 the organs of living animals, independently of physical as well as 

 of chemical forces. The discovery of artificial urea was followed 

 by others in an uninterrupted series, which, besides the practical 

 interest they were entitled to claim, threw a new and clear light 

 upon many processes in organic life. In glancing at some of 

 them, we confine ourselves to cases of more general interest. 



A conspicuous instance of the degree to which synthetical 

 chemistry has enabled us to imitate nature in some of the pro- 

 cesses going on in the bodies of plants and animals is represented 

 by the changes which salicin undergoes. It is to this white and 

 crystalline compound — belonging to the chemical group of gluco- 

 sides — that the leaves of willow and poplar trees owe their bitter 

 taste. Several species of Spircza, while young, also contain salicin, 

 which, during growth, is converted into a volatile oil of reddish 

 color — salicylic aldehyde — an oil which, remarkably enough, is also 

 produced from salicin in the body of the larvae of Chrysomela 

 populi, a beetle feeding on the leaves of poplar-trees. In Spircea, 

 as well as in other plants containing this oil, it is partly trans- 

 formed into salicylic acid, which in its turn in Gaultheria procum- 

 bens and Betula lenta combines with methyl to form a product 

 known as " wintergreen-oil." Now by synthesis we can artifi- 

 cially reproduce all these changes, though pursuing quite a differ- 

 ent way from that which Nature follows. We can convert salicin 

 into salicylic aldehyde ; we can transform this into salicylic acid, 

 and we can produce wintergreen-oil by combining this acid with 

 methyl. We can even manage to prepare salicylic acid and win- 

 tergreen-oil from coal-tar, a substance which, as everybody may 



