106 
THE SCIENCE OF HORTICULTURE. 
To be a little more explicit, we may suppose that all loams contain a portion 
of the vegetable alkali, known in trade by the term Salt of Tartar, or pearl-ash. 
This salt exists neither in the air nor in water ; yet the whole that is imported 
from America and the North of Europe is obtained from the ashes of trees burned 
in the native forests. Therefore, it is more than probable that the soil is the 
storehouse of the whole. Potash and flint unite, and produce what chemists call 
Silicate of Potass, and this can be traced in loams. Lime acts upon this natural 
Salt of Potash, and such of our plants which affect it, take up their constitutional 
supply from the ground : the same may be said of all the mineral salts, — soda, 
common salt, the phosphate of lime, &c, &c. One remarkable fact related by 
Mr. Hoskyns, in a letter to the Hereford Agricultural Society, is worthy of record 
and serious consideration ; it is to the following purport: — 
Mr. Hoskyns once visited the Island of Madeira, where, as every one knows, the 
celebrated wine which bears that name, alone is produced. He ascertained, however, 
that the vines deteriorate by lapse of time, and no longer yield grapes equal to the 
object of the grower, the wine being of inferior quality. It is well known to chemists 
that a certain deposit is formed during the mellowing of wines that require to be 
kept long in the vats, and this gradually assumes the figure of crystalline masses. 
These, when detached, become an article of commerce, under the name of argol, or crude 
tartar, and, when purified and re-crystallised, "cream of tartar ;" this salt is a true 
bi-tartrate of potash, consisting of two proportionals of tartaric acid and one propor- 
tional of the vegetable alkali or potash. The acid is the product of an organic 
process within the vine, from the organic elements, oxygen, hydrogen, and carbon ; 
it is the essential, proper acid of the vine, but it appears to require its specific 
equivalent of potassa to enable it to prepare those juices which are essential to the 
process of wine-making. The soil of Madeira becomes exhausted of its potash, and 
when this loss is effected, the vineyards must be renewed. Mr. Hoskyns saw the 
labourers at work, trenching and excavating to the depth of seven or eight feet ; and 
upon strict inquiry, he ascertained that by thus bringing up soil from a great depth 
the trees were restored, and the juice of the grape perfected. The islanders had no 
other ready means at command, but by labour they were able to effect the desired 
object. We may not be able so to explain the rationale of the process (even admitting 
that potash is really present in the earth) as to direct the renewal of the soil by 
artificial means. Potash could, with the utmost facility, be incorporated ; but the 
knowledge of analytic results in the laboratory will not elucidate the secret opera- 
tions of natural electro-chemistry. We know sufficient to authorise the most refined 
and rigid experiments ; but at present, we must not affect to appreciate the mysterious 
phenomena of nature ; hence the application of saline manures ought always to be 
made with extreme caution, and on a restricted scale, otherwise much injury may be 
done. Knowledge is on the advance, and hopes may be safely entertained ; but 
with such facts as those referred to by Mr. Hoskyns, we ought to combine " practice 
with science," and by all means to work deeply — thus tasking the restorative powers of 
