VOL. LXXXIX.] PHILOSOPHICAL TRANSACTIONS. 551 



Common mortar which had been exposed to the air for a year and three-quarters, 

 had regained -iVo- tns of its full quantity of fixed air. As the preceding experi- 

 ments were tried during the winter, in a room warmed by fire, perhaps under cir- 

 cumstances 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 cal- 

 careous, 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 reason for 

 suspecting that the kind of marble which had been called Dolomite, from M. Do- 

 lomieu, who first remarked its peculiarity in dissolving slowly, might also be simi- 

 lar in its composition. An analysis of this substance was lately given in the 

 Journal de Physique, but this is probably erroneous; for, on examining three speci- 

 mens, 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 Dolomite 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 it, and no quarries of a similar kind are known in Italy; the 2d was 

 said to have been thrown up by Mount Vesuvius; and the 3d was from Iona, one 

 of the western islands of Scotland. In many kinds of common marble, small 

 particles and veins may be observed, which are a long time in dissolving. These, 

 on examination, I discovered to contain a considerable proportion of magnesia; but, 

 as they were probably not quite free from the surrounding marble, I did not ascer- 

 tain the quantity precisely. The crystallized structure which may generally be ob- 

 served in the magnesian limestone, seems to show that it has not been formed by 

 the accidental union of the 2 earths, but must have resulted from their chemical 

 combination. The difficulty of dissolving it, may also arise from the attraction of 

 the different component parts to each other. The mortar formed from this kind of 

 lime, is as soluble in acids as common marble; and the substances of which it con- 

 sists are easily separated. The magnesia may be taken from it by boiling it in 

 muriated lime, and lime is precipitated by it from lime water; but neither of these 

 effects can be produced by the stone, before it is calcined. 



Magnesian limestone is probably very abundant in various parts of England. It 

 appears to extend for 30 or 40 miles, from a little south-west of Worksop, in 

 Nottinghamshire, to near Ferry-bridge, in Yorkshire. About 5 or 6 miles farther 

 north there is a quarry of it, near Sherburn; but whether this is a continuation 

 from the stratum near Ferry-bridge, I have not learnt. From some specimens 

 which were sent me, I find that the cathedral and walls of York are made of it. I 

 have not been able to learn whether there were any shells in the limestone of the 

 tract of country before mentioned. In Mr. Marshall's account of the agriculture 

 of the midland counties, he speaks of the lime made at Ereedon, near Derby, as 



