Agricultural Chemistry. 309 



But Mr. Lawes goes still farther. He wishes to make the 

 world believe, that the good effects of ammonia in the manure 

 were unknown to me — to me, who, so to speak, first discovered 

 ammonia as an agent in agriculture — who have studied most 

 minutely its action in manures, and, of course, knew this action 

 — while my book is full of it, and I have there given a scientific 

 explanation of its effects. But he goes even much farther than 

 this ; for he tries to make it appear that I have recommended, 

 specially, to supply no ammonia to grain crops in the manure ; 

 whereas the only passage in my book, in which I have acci- 

 dentally spoken of the manuring of any special class of plants, 

 and of the advantage of supplying ammonia in the manure, has 

 reference to grain crops : — 



" If we furnish to the soil, which contains ah-eady all the other constituents, 

 ammonia, and to the cereals the phosi^liatcs essential to their growth, in the 

 «vent of their being deficient, we furnish all the conditions for a rich crop." * 

 —See p. 134. 



" 2. By the addition of sulphurised and nitrogenised substances, we create in 

 the soil a source of ammonia, which contributes to the acceleration of the develop- 

 ment of the plants and to the increase of their mass. 



"3. Since the conversion of carbonic acid into a constituent of plants is effected 

 "by the agency of the alkalies and alkaline earths ; since, moreover, without a 

 supply of phosphates no seeds are formed ; it is evident that, when carbonic acid 

 and ammonia are supplied, the growth of plants is not accelerated or promoted, 

 unless the mineral constitutents essential to the assimilation of these substances 

 are simultaneously provided." 



Again, in my ' Dictionary of Chemistry,' Vol. II. p. 633, are the following 

 words (the first number of this volume appeared in 1842, the last in 1848 ; the 

 article ' Manure,' from which the following extract is made, appeared in October, 

 1847, and was written by Dr. W. Hoffman, formerly my assistant in Giessen) : — 



" Let us suppose a field, which contains in great abundance all the mineral 

 constituents wliich the plant requires, but in which — that is, in the soil — carbon 

 and nitrogen are entirely absent. If we sow grain in this field, and if air, water, 

 and the proper temperature be supplied, it will yield a full crop, but we shall not 

 obtain the nuiximum of possible produce. The problem of cultivation is this: to 

 raise to the hii/hcst pitch the produce of the soil. On account of the short time to 

 which the life of our cultivated plants is limited, we can only attain the maximum 

 of their developnaent by giving to them an additional supply of carbonic acid and 

 ammonia, in the soil, besides that which they can obtain from the atmosphere. By 

 means of the roots left in the ground, and by means of the various secretions of 

 the preceding generation of plants, our cultivated fields are always supplied 

 with a sufficient (piantity of carbonaceous matters (humus), which, by their 

 decay, provide an abundant atmosphere of carbonic acid. It is therefore enough, 

 if we add, to tlie nitrogen which is supplied to plants in the ammonia of the 

 atmosphere, nitrogen derived from animal excreta. From these considerations it 

 evidently appears how high is tlie value to agriculture of animal excreta, since, 

 if properly treated, they supply to our fields all the elements Mhieh are required, 

 not only for the natural dcvi-lopment of plants, but also for an artificial increase 

 of that development. 



" These are " (says the author of this paper, in the Dictionary- which bears ray 

 name), "in all essential points, tlu' opinions which Liebig bus expressed on this 

 subject in ditl'erciit parts of his work on Chendstry, in its applications to Agri- 

 culture and Physiology. Kilition, 184()." 



* Mr. Lawcs says (p. 447j, " The efticacy of annnoniacal salts, in yielding an 

 increase of produce, not only in our own experiments, but as a firmly-established 



