96 A PRACTICAL TREATISE 



upon a filter, previously weighed. Dry the filter, and ascertain its increase 

 of weij^'ht, which will indicate how much insoluble matter the quantity of 

 lime submitted to experiment contained. It is easy to judge by the exter- 

 nal quulhies of the insoluble portion, whether argillaceous earth abounds in 

 its composition.' 



The presence o^ magnesia in limestone has been considered 

 pernicious to vegetation when burnt into lime. It had been 

 long- known to farmers in the neighbourhood of Doncaster, and 

 other parts of Yorkshire, Derby, and Nottingham, that lime 

 made from a peculiar species of limestone injured their crops; 

 and that made from the Breedon limestone, in Leicestershire, 

 which there goes under the denomination of ' hot lime,' is so 

 powerful, that it is there seldom used in larger quantities than 

 from 25 to 30 bushels an acre, unless the land be very rich. 

 A series of experiments were made upon the former by Mr. 

 Tennant, who discovered that it contained magnesia, and on 

 mixing some calcined pure magnesia with earth, in which he 

 sowed different kinds of seeds, he found that they either died 

 or vegetated very imperfectly; he therefore came to the con- 

 clusion that its effects were prejudicial. This is thought to 

 have been occasioned by its retaining its caustic quality longer 

 than pure lime ; and that, if used to excess, it has a poisonous 

 effect on vegetables, though, 'on poor soils,' it has been said 

 * neither to receive water so rapidly, nor to part with it so 

 freely, as lime; and in this respect it seems to hold an inter- 

 mediate property between lime and clay.' Experiments have 

 also been made by Sir Humphry Davy and other chemists, 

 from which it may be collected that, although, when calcined, 

 as lime, it may become pernicious to land, if laid on in too 

 large quantities, yet that, in its mild state, it is a useful con- 

 stituent of soils. One of the most fertile parts of Cornwall, in 

 the neighbourhood of the Lizard, is a di.^^trict in which the land 

 abounds in magnesian earth. It is, indeed, one of the mildest 

 absorbents with which we are acquainted, and upon ground 

 which is infested with sorrel, its application is an immediate 

 remedy. Magnesian limestone is usually of a pale yellow or 

 brown colour, and is found in many parts of England, as well 

 as Ireland ; it effervesces when plunged in acid, though it only 

 dissolves slowly. 



Its analysis requires a process too tedious to be here stated, 

 but its existence in lime, in a pure state, may be ascertained 

 by the following test: — 



Having taken out all the mineral oxide, next pour into the fluid a solution 

 of neutralized carbonate of potassa, continuing to do so until it will effer- 



