NA TURE 



193 



THURSDAY, JANUARY 4, 1877 



THE FARADAY LECTURE FOR 1875 

 The Life Work of Liebig in Experimental and P/iilo- 

 sophic Chemistry. By A. W. Hofmann, F.R.S,, &c. 

 Delivered before the Chemical Society of London, 

 (London : Macmillan and Co.) 



IN this volume we have given us a sketch of the labours 

 of Liebig in the domain of Pure and Applied Che- 

 mistry, and also an account of his manifold investigations 

 in the direction of its Application to Agriculture and 

 Physiology. 



■ Prof. Hofmann has been induced lo take the works of 

 this great chemist as the theme for the Faraday lecture, 

 not only from its being a subject in itself rich in most inter- 

 esting matter, but, that from Liebig's studies on the rela- 

 tion and mutual bearing of the facts discussed by him, he 

 was led to the conception of general laws elucidating 

 chemical phenomena ; thus standing beside Faraday as a 

 fit representative of our century to future generations. 

 Notwithstanding the great reputation Liebig now pos- 

 sesses, Prof Hofmann seems to think that at the present 

 time, we being almost contemporaneous with this great 

 chemist, are not in a position to give to his works such 

 appreciation as will be yielded them in the future ; on 

 this point Prof. Hofmann says : — 



"As those who wander in a mountain chain cannot 

 appreciate the sky-reaching grandeur of its lofty peaks as 

 well as those who remotely from the plains beneath con- 

 template its snow-crowned summits, so we, the contem- 

 poraries of Faraday and Liebig cannot perceive the full 

 dignity of their commanding forms— the philosophic pin- 

 nacles of this century — as they will hereafter appear to 

 distant generations of posterity. In these days Faraday 

 and Liebig will be looked up to with such reverence as it 

 is ours to offer to the mighty spirits of the past — to such 

 giant figures as those of Galileo, Kepler, Newton, and 

 Lavoisier. And as that bright constellation shines on us 

 from the misty darkness of the past, so will the names of 

 Faraday and Liebig — stars of co-equal lustre — throw for- 

 ward their bright beams on our successors through the 

 far-reaching vista of ages yet to come." 



Although expressing himself at the outset embarrassed 

 by the richness of the subject, and consequently the diffi- 

 culty of making any proper classification or selection of 

 the many interesting investigations and discoveries to be 

 discussed. Prof. Hofmann must be congratulated on the 

 very successful result which has crowned his endeavours. 



Commencing with a short review of the general work 

 of Liebig with regard to the elaboration of apparatus and 

 analytical methods for chemical research, Prof. Hofmann 

 proceeds to speak of the great power Liebig had in im- 

 parting knowledge to others, and his influence over the 

 mind of his pupils. He next draws attention to the re- 

 semblance between the labours of Liebig and Faraday in 

 abstract science, and the abundant results they have pro- 

 duced in their applications to the useful arts. 



In the field of agricultural chemistry, in his investigation 

 of the laws regulating the growth of plants, we learn 

 from Prof. Hofmann that Liebig first penetrated the 

 doubt and uncertainty which had previously existed, 

 establishing with certainty the relation which exists 

 between the growing plant and soil and air in which 



it lives. Standing as a monument of his most ex- 

 haustive researches on this point, we have his two works : 

 " Chemistry in its Application to Agriculture and Physio- 

 logy," and " The Natural Laws of Husbandry," this latter 

 work constituting the first perfect treatise on the philo- 

 srphy of agriculture which had appeared up to that time. 

 To Liebig is also due the knowledge we now possess, that 

 for proper vegetable growth the plant must be supplied 

 through the land with those constituents which are found 

 in its ash ; and, as a sequence following from this, the 

 fact, that should the soil become deprived of such con- 

 stituents, it will be unfit for further plant growth till the 

 proper saline ingredients are returned to it. With the 

 knowledge acquired on such points he was naturally led 

 to the production of artificial manures as a means for the 

 fertilisation of land impoverished and exhausted by the 

 crops grown upon it. 



Passing from Liebig's labours in agricultural chemistry 

 to those in the higher branch of biology, we find his cis- 

 coveries producing no less perfect and important results. 

 Although many isolated researches, as those of Chevreul, 

 Berzelius, Gmelin, and Tiedeman, had been already con- 

 ducted on certain constituents of the animal economy, 

 still we owe to Liebig the collection of these widespread 

 attempts into a " focus " for the elucidation of the phe- 

 noiiiena of animal life. Of Liebig's chemico-biological work 

 perhaps the best instances we can refer to are his " Investi- 

 gations into the Origin of Animal Heat," his " Theory 

 with regard to the Nutrition of Animals," and his " Doc- 

 trine of the Origin and Function of Fat in the Animal 

 Economy." In the first of these inquiries he reviews the 

 ideas of Lavoisier and Laplace, and the experiments of 

 Dulong and Despretz, pointing out the errors of experi- 

 ment the two latter investigators had fallen into, and 

 from his own minute calculations proving the sensible 

 heat of the animal body to be explained by thS processes 

 of combustion carried on within the organism. From his 

 inquiries into the chemical nature of food, Liebig was led 

 to his theory that the vegetable stands in a position inter- 

 mediate between the mineral and the animal. The animal 

 being unable to assimilate inorganic compounds, the 

 vegetable acts as a means for transforming the mineral 

 molecules into those of a higher order fit for the proper 

 maintenance of the animal organism. The facts neces- 

 sary for the support of his theory are to be found in the 

 identity in composition of the nitrogenous principles, 

 animal and vegetable, albumin, casein, and fibrin ; a fact 

 previously pointed out by Mulder, but exactly determined 

 through analysis either by Liebig^or his pupils. 



In the views promulgated by Liebig that it is in the 

 animal organism, through the transformation of starch, 

 sugar, &c., that the chief formation of fat takes place, he 

 was led into a long and animated controversy with Dumas 

 and Boussingault ; but in this, as in other of his discus- 

 sions, experiment has decided in favour of Liebig, 

 Although the experiments of his opponents proved the 

 existence of fat in vegetables, it was nevertheless in quan- 

 tities quite insufficient to account for the amount found 

 in animals when fed artificially on vegetable food alone. 

 Like his investigations in agricultural chemistry, Liebig's 

 discoveries in the biological branch yielded their propor- 

 tion of practical applications, and from his investigations 

 of the composition and nutrition of the animal body arose 



