Recent Publications on Manures. 87 



says, " the first original plants must have got all their carbon from 

 the air, unless what existed in the water of the soil : on the 

 bare rock, however, vegetation is stunted, and we cannot deny 

 that organic matter deposited in the soil increases the produce, 

 and, if crops are carried offthe soil without manuring, it becomes 

 exhausted. Partly it is undoubtedly got from the air, as some 

 plants live suspended in the air, and vegetable matter accumulates 

 in peat bogs, and marshy soils also produce crops without manure. 

 Water is able to absorb 95 times its own bulk of ammonia (some 

 have rated its absorbing powers higher; the temperature of the 

 water increases its powers). Ammonia is also absorbed by porous 

 substances and soils : it has a considerable affinity for acids, but 

 less than the other alkalies; lime sets it free in great quantities. 

 The carbonic acid excreted by the roots, will assist to extract 

 the ammonia from the pores of the soil, and the porous sub- 

 stances in the soil." He thinks Liebig's theory of the action of 

 gypsum on the sulphate of lime insufficient, "as it does not 

 account for all the nitrogen in the excess of crop." The inform- 

 ation to be got from the professor's lectures on these subjects is 

 highly interesting : when great chemical knowledge is united to 

 caution in inducing inferences, it is not so apt to lead us astray as 

 when a brilliant imagination carries us to the very verge, if not 

 beyond, the bounds of truth. The chapter on the transformation 

 of the organic substances of plants, so far as chemistry has yet 

 been able to produce them, is of great value. Dr. Madden, on 

 the action of the sulphate of lime, says, " when more than \ per 

 cent of ammonia is given off to the soil, when more than —-$ 

 part of the bulk of the soil is given offatany place by the manure 

 in the soil, if sulphate of lime is present, which it generally is, 

 especially in peaty soils, sulphate of ammonia will be formed. If 

 this is again dissolved in water and brought in contact with 

 carbonate of lime, carbonate of ammonia and sulphate of lime 

 will be produced." In some former essays in the Quarterly 

 Journal of Agriculture, apparently from the pen of the same 

 intelligent chemist, great doubts were entertained of the sulphate 

 of lime always acting in the way pointed out by Professor 

 Liebig. There is much to learn yet on many of these subjects, 

 and practical men should balance well the statements brought 

 forward by chemists, before committing themselves to great 

 expense in trials. It is safest to conduct experiments on a small 

 scale, till they are well established. 



On the subject of humus, "Dr. Madden, in the Prize Essay on 

 Draining, published, in the Highland Society's Transactions 

 {Quarterly Journal of Agriculture for December, 184 1), considers 

 the soluble matter of soil an organised extract, which he deno- 

 minates humus, but prefers the name of ulmic acid for its product 

 to humic acid, He defines ulmic acid as consisting of 1 atom of 



G 4 



