goes. When examining the nature of hydro- 

 chloric and hydriodic acids, Davy gave it out aa 

 probable that ihe acidifying principle is not, as 

 was supposed, oxygen, but hydrogen. In the 

 above mentioned acids it is easily seen, and he 

 wished to extend it to others also. Liebig, in 

 his inquiry into the nature of organic acids, has 

 found a wider range of comparison, and has set 

 in a point of view which few persons are now 

 inclined to contradict, and which all must find 

 to be a beautiful explanation of an extensive 

 class of natural appearances. 



He sajs. '■ hydrated acids are compounds of 

 one or more elements with hydrogen, in which 

 hydrogen may be replaced by metals." 



If an acid be so constituted, the hydrogen, ca- 

 pable of being replaced by a metal, is the trae 

 mea.sure of the capacity of saturation ; the re- 

 maining elements may then be termed the rad- 

 ical, as chlorine or iodine in the cases of hydro- 

 chloric and hydriodic acids. If this be the case, 

 any addition of elements to the radical will have 

 no effect on the capacity of saturation. 



" But if the hydrogen increases or diminish- 

 es, the capacity of saturation increases and di- 

 minishes in a like ratio." 



'• If the above definition of a radical he cor- 

 rect, we see that any addition to it will have no 

 effect on the capacity of saturation of the acid, 

 so long as the amount of hydrogen remains .un- 

 altered." 



In conformity with this principle, he has used 

 in his work on organic chemistry 3fhis formula 



for acetate of Soda — for example, ac Na ; 



whereas, we are accu.stomed generally to use 

 base first, as Na X So 3, for sulphate of soda. 

 This theory has also been fully extended by 

 Professor Graham, who has taught us the true 

 position of water and bases in inorganic salts, 

 and has termed sulphuric acid sulphate of wa- 

 ter, just as green vitriol is termed sulphate of the 

 oxide of iron. The first is So 3 X H ; the 

 second. So 3 X Fe 0; the iron in one takes the 

 place of the hydrogen in the other. But this 

 subject is not one likely to be of much practical 

 use at present. The substitution of the alkalies 

 is of more interest. 



An idea prevails among us that Liebig is a 

 farming chemist only ; that his greatest pleasure 

 is to see beautiful fields manured in a chemical 

 manner, and growing wheat and turnips ac- 

 cording to the exact methods which he has laid 

 down. In this -we are mistaken ; Professor Lie- 

 big is a philosopher, or, according to the Ger- 

 man expression, a searcher of nature ; and the 

 great experience which many years devoted to 

 organic chemisti-y had given him in the modes 

 of operation of such bodies, whilst it peculiarly 

 fitted him for investigating agricultural and phy- 

 siological subjects, naturally also led him into 

 them. At the earlier part of this century the 

 lau-s of combination were developed. The 

 chief workers in this field are still living — nu- 

 merous compounds %\ere formed and obtained 

 formed in nature ; but inorganic chemistry was 

 chiefly studied, and the most highly organized 

 substances -were treated in the same manner as 

 compounds of sulphuric acid and iron, or any 

 other mineral substance. Boyle, or rather the 

 chemists of his time, analyzed a piece of green 

 wood by putting it up the chimney, when it 

 burned, and they perceived four elements — fire, 

 air, earth, and vvatcr — which we are apt to say 

 were combined by a vital vegetable principle : 

 one of those facts is as near the truth as tlie 

 other, for facts we may call them, a.s, however 



(371) 



imperfectly expressed, they fall within the bor- 

 ders of received truth. If wc analyze organic 

 compounds, and obtain from them instead of 

 fire a certain amount of specific heat ; instead of 

 air, a certain amount of nitrogen ; and, instead 

 of earth and water, a certain amount of phos- 

 phates, silicates, oxygen, and hydrogen : we ex- 

 press the true compo.sitions of the body more 

 accurately than the friends of Boyle, but we are 

 no wiser as to the laws of gi'owth and decay, no 

 nearer to the principles which vitality employs 

 to exhibit its various appearances ; because vi- 

 talitj- itself had ceased prior to the view which 

 we have obtained of the elements employed in 

 its service. If, however, having collected these 

 facts, having obtained a knowledge of the com- 

 plex organic compounds which are used for tlie 

 phenomena of life, we begin to observe their 

 action towards each other, we have ascended 

 into a region as far above the former, as the 

 complicated machinery of kingdoms, such as 

 England, France, or Germany, is above the 

 simple relations of unsocial, independent, and 

 walled villages of earlier times. The physiolo- 

 gy of plants and animals is" then a step m ad- 

 vance of the usually termed organic chemistry, 

 and when we are taught the parts albumen or 

 sugar play in the system, we have more know- 

 ledge and more power than wheu we can mere- 

 ly tell their composition. It is well known that 

 this field has received from Professor Lit^big the 

 first cultivation — that the first icgular crop was 

 sown and reaped by his hands. It is vain for 

 us to say that others before him saw so far ; it is 

 not unfrequently the case, that the end is seen 

 long before any of the intermediate stations. — 

 Absolute certainty often aiTives before clear rea- 

 soning, and it is often hard for us to prove the 

 most unquestionable truths. It is from this cause 

 that many discoveries have been claimed for 

 men who named them only, but could not pros- 

 ecute them, that the dark hints given in ancient 

 volumes have seemed to some men to indicate a 

 superior knowledge to our days, that a m«ta- 

 physical inquh-er has been honored as the dis- 

 coverer of the atomic theorj-, although ignorant 

 of chemical combination; and Egyptians been 

 made the discoverers of the laws of acoustics, 

 because they had an imase which emitted 

 sounds, by la\vs which we have not yet learned 

 to put in motion. 



Davy said, " The laws of mind are probably 

 not far different from the laws of corpuscular 

 motion ; ever\- change in our .sensations must be 

 accompanied by a corresponding change in the 

 organic motion of the body." 



This he said when but a youth, and it is a 

 very good instance of the mode iu which im- 

 mense series of discoveries are often anticipated 

 by si)eculative men. It not only may be said to 

 include what has been discovered, but grasps at 

 much that we maj- safely expect some day to 

 be known. It anticipates the time \vhen the ac- 

 tion of our feelings on the system shall be per- 

 fectly known, and almost leaves as an insignifi- 

 cant thing the action of the food, of the air, and 

 of exercise. To teach us how to find some of 

 this knowledge, and to give us the first fruits, 

 has been the task of Professor Liebig : and al- 

 ready has the whole of this country, with many 

 others, arisen unanimously, to express by the 

 most energetic action, the lively impression of 

 truth, which the principles taught by liim have 

 made upon them. The fanner no longer suppo- 

 ses that barren land can become fertile by dip- 

 ping the seed to be sown in a solation of a salt. 



