4 
‘On different Sorts of Lime ufed in Agriculture. 2id 
‘were fown in uncalcined magnefia; but, though they {prouted, 
the leaves never rofe above the furface, and the plants were 
entirely without roots, nor did they appear to grow better in 
magnefia which had been wafhed in water containing fixed 
air, Calcined magnefia was, however, much more deftruc- 
_tive, as the feeds would not come up in it. To compare its 
effects on vegetables with thofe of lime, each of thefe carths 
was mixed, in different proportions, with fand, in fmall cups, 
in which feeds were then fown. The lime was obtained from 
marble; and, before it was put into the fand, was made to 
fall to powder, by being moiftened with water. In a mix- 
ture of four ounces of fand with three or four grains of cal- 
cined magnefia, it was a long time before the feeds came up, 
and the plants had hardly any roots or ftalks ; and, with ten 
grains or more of magnefia, there was no appearance of ye- 
getation, Thirty or forty grains of lime did not retard the 
growth of the feeds more than three or four of magnefia, and 
the injurious effects were not fo lafting. The lime, by ab- 
forbing fixed air, foon loft its deftructive properties ; fo that, 
after keeping thefe mixtures four or five weeks, feeds were 
found to grow in that with forty grains of lime, nearly as 
well as in pure fand; but, in that with four grains of mag- 
nefia, they produced only the feed-leaves, as was defcribe 
before. It was neceflary occafionally to break in pieces the 
{and which had fo much lime, as it would otherwife have 
een too hard to admit the feeds to penetrate through it. 
Plants will bear a much larger proportion of magnefia in ve- 
getable foil than in fand: with twenty grains, however, of 
calcined magnefia, in as much foil as was equal in bulk to 
four ounces of fand, the feeds produced only the feed-leaves 
without roots; and, with about forty grains, they were en- 
tirely prevented from coming up, 
In countries where the magnefian lime is employed, it 
was faid, that the barrennefs of any {pot on which a heap of 
it had been laid, would continue for many years. To learn 
how far it could by time be deprived of its injurious quali- 
ties, I procured fame pieces of mortar, made of this {pecies 
of lime, from two houfes, ane of which had been built three, 
and the other eight years: they were taken from the outfide 
Re 2 af 
