652 



FARMERS' REGISTER 



[No. 11 



The limestonee containing alumina and silica 

 are less fitted for the purposes ol' manure than 

 pure limestones; but the lime formed from them 

 has no noxious quality. Such stones are less ef- 

 ficacious, merely because they furnish a smaller 

 quantity of quicklime. 



1 mentioned bituminous limestones. There is 

 very seldom any considerable portion of coally 

 matter in these stones; never as much as five parts 

 in 100 ; but such limestones make very good 

 lime. The carbonaceous matter can do no injury 

 to the land, and may, under certain circumstances, 

 become a Ibod of the plant, as is evident from 

 what was stated in the last lecture. 



The subject of the application of the magne- 

 eian limestone is one of great interest. 



It had been long known to farmers in the neigh- 

 borhood of Doncaster, that lime made from a cer- 

 tain limestone applied to the land often injured the 

 crops considerably, as I mentioned in the introduc- 

 tory lecture. Mr. Tennant, in making a series of 

 experiments upon this peculiar calcareous sub- 

 stance, found that it contained magnesia ; and on 

 mixing some calcined magnesia with soil in which 

 he Rovved different seeds, he found that they either 

 died, or vegetated in a very imperfect manner, 

 and the plants were never healthy. And with 

 great justice and ingenuity he referred the bad ef- 

 fects of the peculiar limestone to the magnesian 

 earth it contains. 



In making some inquiries concerning this sub- 

 ject, I found that there were cases in which this 

 magnesian limestone was used with good effect. 



Amongst some specimens of limestone which 

 Lord Somerville put into my hands, two marked 

 as peculiarly good proved to be magnesian lime- 

 stones. And lime made from the Breedon lime- 

 stone is used in Leicestershire, where it is called 

 hot lime ; and I have been informed by farmers 

 in the neighborhood of the quarry, that they era- 

 ploy it advantageously in small quantities, seldom 

 more than 25 or 30 bushels to the acre. And that 

 they find it may be used with good effect in larger 

 quantities upon rich land. 



A minute chemical consideration of this ques- 

 tion will lead to its solution. 



Magnesia has a much weaker attraction for car- 

 bonic acid than lime, and will remain in the state 

 of caustic or calcined magnesia lor many months, 

 though exposed lo the air. And as long as any 

 f austic lime remains, the magnesia cannot be com- 

 bined with carbonic acid, for lime instantly attracts 

 carbonic acid fi-om magnesia. 



When a magnesian limestone is burnt, the 

 magnesia is deprived ofcarbonic acid much sooner 

 ihan the lime; and if theie is not much vegetable or 

 animal matter in the soil to supply by its decom- 

 position carbonic acid, the magnesia will remain 

 for a long while in the caustic stale; and in this 

 state acts as a poison to certain vegetables. 



I have made, I fiave satisfied myself that it arrests 

 equally vinous and the putrid fermentation, and that 

 in close vessels it may be used for preserving both 

 animal and vegetable substances. When it promotes 

 the solution of vegetable substances, it is probably 

 owing either to forming with them soluble compounds, 

 as in the instance of ulmin, (before mentioned,) or 

 in promoting the production of proximate principles 

 from their elements, capable of entering into union 

 with it, and with -which it forms such soluble com- 

 poujids. — J. D. 



And that more magnesian lime may be u?ed upon 

 rich soils, seems to be owing to the circumstance, 

 that the decomposition of the manure in them sup- 

 plies carbonic acid. And magnesia in its mild 

 state, i. c. fully combined with carbonic acid, 

 seems to be always a useful constituent of soils. 

 I have thrown carbonate of magnesia (procured 

 by boiling the solution of magnesia in super-carbo- 

 nate of potassa) upon grass, and upon growing 

 wheat and barley, so as to render the surface 

 white: but the vegetation was not injured in the 

 slightest degree. And one of the most fertile 

 parts cf Cornwall, the Lizard, is a district' in 

 which the soil contains mild magnesian earth. 



The Lizard Downs bear a short and green 

 grass ; which feeds sheep, producing excellent 

 mutton; and the cultivated parts are amongst the 

 best corn lands in the country. 



That the theory which I have ventured to give 

 of tbe operation of magnesian lime is not unfound- 

 ed, is shown by an experiment which I made ex- 

 pressly lor the purpose of determining the true na- 

 ture of the operation of this substance. 1 took 

 four portions of the same soil: with one I mixed 

 J, of its weight of caustic magnesia, with another 

 I mixed the same quantity of magnesia and a pro- 

 portion of a fat decomposing peat equal to one- 

 fourth of the weight of the soil. One portion of 

 soil remained in its natural state: and another was 

 mixed with peat without raasnesia. The mixtures 

 were made in December 1806, and in April 1807 

 barley was sown in all of them. It grew very 

 well in the pure soil; but better in the soil contain- 

 ing the magnesia and peat, and nearly as well in 

 the soil containing peat alone: but in the soil con- 

 taining the magnesia alone, it rose very feeble, and 

 looked yellow and sickly. 



I repeated this experiment in the summer of 

 1810 with similar results; and I found that the 

 magnesia in the soil mixed with peat became 

 strongly effervescent, whilst the portion in the un- 

 mixed soil gave carbonic acid in much smaller 

 quantities. In the one case the magnesia had 

 assisted in the formation of a manure, and had be- 

 come mild ; in the other case it had acted as a 

 poison. 



It is obvious, from what has been said, that lime 

 from the magnesian limestone may be applied in 

 large quantities to peats; and that where lands 

 have been injured by the application of too large 

 a quantity of magnesian lime, peat will be a pro- 

 per and efficient remedy. 



I mentioned that magnesian limestones effer- 

 vesced little when plunged into an acid. A sim- 

 ple test of magnesia in a limestone is this circum- 

 stance, and its rendering diluted nitric acid or aqua 

 Ibrtis milky. 



From the analysis of Mr. Tennant, it appears 

 that the inagneigian limestones contain from 

 20-3 to 22-5 magnesia. 

 29-5 to 31-7 lime. 

 47*2 carbonic acid. 

 0*8 clay and oxide of iron. 



Magnesian limestones are usually colored brown 

 or a p-rde yellow. They are found in Somerset- 

 shire, Leicestershire, Derbyshire, Shropshire, Dur- 

 ham, and Yorkshire. I have never met with any 

 in other counties in England; but they abound in 

 many parts of Ireland, particularly near Belfast. 



The use of lime as a cement is not a proper sub- 

 ject for extensive discussion in a course of lectures 



