CHEMISTRY OF THE NINETEENTH CENTURY. 621 



of inquiry in such investigations would be intelligible only to those 

 specially versed in the study of chemistry, we must refrain from con- 

 tinuing the long list of Liebig's studies. Two of the many new sub- 

 stances prepared by him may be named, however, because they have 

 been heard of by everybody as the anaesthetics most largely used by 

 medical men at the present day. These are chloral, with its hydrate, 

 and chloroform, Liebig did not at the time know that these substances 

 were destined to become potent " for the relief of man's estate," as we 

 know them now. It was not until 1847, or fifteen years after its dis- 

 covery, that Sir James Simpson, the eminent surgeon of Edinburgh, 

 used chloroform for the first time as an anaesthetic. Chloral was not 

 applied in medicine until a still later period, when thirty-five years had 

 elapsed since its discovery. Liebig adopted and strenuously advocated 

 the theory of "compound radicals," which was at first accepted also by 

 Berzelius ; but when the latter found that some of Liebig's compound 

 radicals contained oxygen, he opposed the radical theory as incom- 

 patible with his own electro-chemical theory. A long controversy 

 was then begun between Liebig and Berzelius. One of the radicals, 

 the existence of which was suggested by Liebig, was ethyl, which he 

 conceived entered into the composition of alcohol and of ether. His 

 ideas have won their way, and modern chemists have universally 

 accepted the theory of ethyl and similar radicals. 



The investigations of Liebig on physiological chemistry, especially 

 his researches on the nutrition of plants and animals, gave rise to the 

 modern scientific system of cropping the soil, by repairing artificially 

 the drawn-off phosphates, supplying nitrogenous materials, and so on. 

 The now very extensive industry of the artificial manure manufacture 

 is of Liebig's creation; and the like may be said of whatever scientific 

 principles guide the feeder of cattle in selecting the food for his stock. 

 Those conversant with agriculture best know the vast impulse it has 

 received in recent times by the scientific practice which was first 

 advocated and made possible by the Giessen Professor of Chemistry. 



No science ever received from a single device a greater impulse 

 than did organic chemistry by Liebig's method of analysing organic 

 substances into their ultimate elements. The substance to be ana- 

 lysed is mixed with oxide of copper in a tube of hard glass, which is 

 heated by charcoal in a convenient apparatus. The hydrogen of the 

 organic substance is converted into water, and as the products of the 

 combination making their exit from the tube first pass through a tube 

 containing a substance capable of absorbing all the moisture, the 

 increase of weight received by the tube is the weight of water pro- 

 duced in the experiment. The carbonic acid gas which has been 

 formed by the union of the carbon of the organic substance with as 

 much oxygen as it can take up, passes on, and is absorbed in a second 

 tube containing a solution of potash. The tube designed by Liebig 

 for this purpose, simple piece of apparatus though it be, shows the 



