212 On different Sorts of Lime ufed in Agriculture. 
of the building, where they had been expofed to the ‘air. 
After they were reduced to powder, feeds were fown in them. 
Only a few came up, and even thofe produced merely the 
" feed-leaves, without any roots. As plants would grow in 
the limeftone from which this fpecies of lime was formed, 
although not in the mortar made from it, I wifhed to know 
what proportion of the fixed air, originally contained in the 
limeftone, had been abforbed by the mortar. For this pur- 
~pofe a piece of it was finely powdered, to render it of an uni- 
form quality: it was then tried how much of this powder, 
and of the limeftone, would -faturate the fame quantity of 
acid: by this means I afcertained the proportions of lime- 
{tone and mortar, containing equal quantities of the magne- 
fian lime. ‘The fixed air being obtained from them in thofe — 
proportions, and meafured in an inverted veffel, with quick- 
filver, it was found that the mortar which had been expofed 
three years had abforbed 43, and that of eight years only 
47 hundredths of the quantity originally contained in the 
himeftone. I was not able to obtain any mortar which had 
been made earlier, though it might deferve to be known how 
much fixed air it was ultimately capable of abforbing. Com- 
mon mortar, which had been expofed to the air for a year 
and three quarters, had regained 63 hundredths of its full 
quantity of fixed air. 
As the preceding experiments were tried during the winter, 
in a room warmed by fire, perhaps under circumftances more 
favourable to vegetation, the fame quantity of magnefia would 
not be equally pernicious. 
Magnefian limeftone may be eafily diftinguifhed from that 
which is purely calcareous by the flownefs of its folution in 
acids, which is fo confiderable, that even the fofteft kind of 
the former is much longer in diffolving than marble. - From 
this property of the magnefian limeftone, there appeared to 
be reafon for fufpecting that the kind of marble which had 
been called Dolomite, from M. Dolomieu, who firft re- 
marked its peculiarity in diffolving flowly, might alfo be 
fimilar in its compofition. An analyiis of One fubftance 
was lately given in the Journal de Phyfique : but this is pro- 
bably erroneous ; as upon examining three fpecimens, they 
were 
oe oe: ¢ 
