of Lime used in Agriculture. 309 
with quicksilver, it was found, that the mortar which had been 
exposed three years had absorbed 43, and that of eight years, 
only 47 hundredths of the quantity originally contained in the 
limestone. I was not able to obtain any mortar which had 
been made earlier, though it might deserve to be known how 
much fixed air it was ultimately capable of absorbing. Com- 
mon mortar, which had been exposed 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 circumstances more 
favourable to vegetation, the same quantity of magnesia would 
not be equally pernicious. 
Magnesian limestone may be easily distinguished from that 
which is purely calcareous, by the slowness of its solution in 
acids, which is so considerable, that even the softest kind of the 
former is much longer in dissolving than marble. From this 
property of the magnesian limestone, there appeared to be rea- 
son for suspecting that the kind of marble which had been 
called Dolomite, from M. Dolomieu, who first remarked its 
peculiarity in dissolving slowly, might also be similar in its 
composition. An analysis of this substance was lately given in 
the Journal de Physique, but this is probably erroneous ; for, 
upon examining three specimens, they were found to consist of 
magnesia and calcareous earth, like the magnesian limestone ; 
so that it ought, no doubt, to be considered as the same’ species 
of stone, but in a state of greater purity. The pieces of Dolo- 
mite were from different places; one of them being found among 
the ruins of Rome, where it is thought to have come from 
Greece, as many statues of Grecian workmanship are made of 
mdccxcix. S s 
