A (jricu It lira I Chcm istry . 
491 
ingredionts), hccaiise the nitrogen of vegetation is furnisltedhy the alninsphere, 
<tnd vot hij the soil. Hence also we caiiuot augment the fertility of our fields, 
or their powers of production, by supplying them witli manures rich in nitro- 
gen, or with ammoniacal salts alone. Tliecmps oa u field diminish or increase 
in exact proportion to the ditniiiHtion or increase of the mineral substances con- 
veyed to it in muHKre." — 4</( Edition, p. 210. 
From this short recital, the reader will be able to form a 
judgment, of what were the prevailing ideas, and what the points 
in question regarding manure, and therefore what was the extent 
of the meaning of Baron Liebig, when he wrote the sentences 
quoted above, and considered it so essential to attribute a pre- 
ponderating value and importance to the mineral constituents 
of manure. And it was in reference to the conclusions arrived 
at by the facts and arguments above referred to, taken in con- 
nection with a consideration of the sources and mineral composi- 
tion of animal excrements, that Baron Liebig in the preface to 
the 3rd and 4tli editions of his main work (published respectively 
in 1843 and 1847), said :— 
"And I am now, for the first time since the completion of these labours, 
in a situation to give a simjjle and deterniinate expression to my view of the 
origin of animal excrements, and of the cause of their beneficial eflects on 
the growth of all vegetables." 
To vindicate himself, however, from the imputation now made 
by most writers on the subject, that in these arguments and 
conclusions he has underrated the value and importance of 
nitrogen or ammonia within the soil, Baron Liebig quotes in his 
' Principles,^ recently published, the following sentence, occurring 
in the same cliapter of his work as that from which we have 
made the extracts given above. 
" In order to obviate any misunderstanding, we must again draw attention 
to the fact, that this explanation is not in any way contradicted by the effects 
produced on the application of artificial ammonia, or of its salts. Ammonia is, 
and will continue to be, the source of all the nitrogen of plants ; its supplj- is 
never injurious ; on the contrai-y, it is alwavs useful, and, for certain purposes, 
indispensable." — ith Edition, p. 212. 
The above vindicatory sentence, quoted from his previous 
work, Baron Liebig now adduces with the following preface :— 
" In order not to excite new doubts, and in order to put an end to a mis- 
vnderstanding, tvhich I thought, hut vainly, as it appears, I had rendered 
impossible in my ivorJc, I repeat here what I said in that v-orl\" — Principles, 
p. 107. 
It would have been more candid if Baron Liebig had given 
the paragraph in question to the end ; for, in what immediately 
succeeds to th.e sentences which he here brings forward, is 
contained the clearest proof that there has been no misunder- 
standing such as he here complains of.* The continuation in his 
work is as follows : — 
* INIr. Maskelyne also, in the 'Saiur'a." Teview ' of December 15, gives the 
