we 
178 Bibliography. 
culturist and physiologist. Since the time of Sir Humphry Davy 
no champion of agricultural chemistry has before appeared, and this 
science, without which no rational system of agriculture can be hoped 
for, has been apparently neglected. 
Great stress has been laid, by chemists and vegetable physiologists, 
on that constituent of soils which they have variously designated as hu- 
mus, humin, coal of humus, humic acid, ulmin, extractive matter, geine, 
soluble and insoluble, and apotheme. he modifications of humus, 
which are soluble in alkalies, have been called humic acid, while those 
which are insoluble have been described as humin, and coal of humus. 
Berzelius, in 1833, published, in the memoirs of the Stockholm Acad- 
emy,* an account of two new acids, the crenic and the apocrenic, found 
in the waters of Porla well, in Sweden, and which he had previously 
(1807)+ designated in his examination of those waters, under the appel- 
lation of extractive matter; and it will be seen by our notice of Dr. 
Jackson’s geological survey of Rhode Island, in this number, that he 
has proved extensively the existence of these two acids in the soils of 
that State, as well as in certain natural waters. It is this substance, 
we repeat, by whatever name it is called, to which so much impor 
tance has been attached by writers on vegetable physiology, and by 
agricultural chemists, as probably constituting an important part of 
the food of plants. 
‘The opinion that this substance is extracted from thee 
roots of plants, and that the carbon entering into its ¢ ‘ 
ral, 
serves in some form or other to nourish their tissues, is 50 § 
and so firmly established, that hitherto any new argument in its favor 
_ has been considered as ind dee: the obvious difference in the 
growth of plants, according to the known abundance or scarcity 0 
humus in the soil, seemed to afford incontestable proof yy ae 
ness. Yet this position, when submitted to a strict examination, 1° 
found to be untenable, and it becomes evident, from the most cone 
sive proofs, that humus, in the form in which it exists in the soil, 
not yield the smallest nourishment to plants.” ‘ 
“The names given to these substances might lead io the suppos 
tion that their composition is identical. But a more erroneous notion 
could not be entertained. Thus, humic acid, obtained by the action 
of hydrate of potash on saw-dust, contains, according to the accurate 
analysis of Peligot, 72 per cent. of carbon, while that from turf and 
brown coal contains, according to Sprengel, only 58 per cent.; t ~ 
produced by the action of dilute sulphuric acid on sugar, 57 pet eel 
and that lastly which is obtained from sugar or from starch, by ner 
* Kong. Vet. Acad. Had. 1833, p. 18. Poggendorff’s Annalen, xx1X- 1, end oe 
Also, Thomson’s Chemistry of Organic Vegetable Bodies, pp. 146, 183°. 
| Afhandlingar, p. 145. 
