FARMERS' REGISTER— MAGNESIA. 



431 



surface of f^rassy turf, and an equal quantity of 

 lime spread on a similar extent of other grassy 

 turf; but could discern no difference in their ef- 

 fects during the summer.' 



After we had considered your correspondent's 

 criticisms, the same gentleman, in conjunction 

 with myself and others, instituted a new set of ex- 

 periments. 



On 22d May 1806, six pots were sunk in a gar- 

 den plot, and each had inserted nearly an equal 

 number of the seeds of oats and peas. 

 No 1. The standard, contained simple earth. 



2. Magnesia, by measure yV mixed with earth. 



3. Do. _ _ I do. 



4. Sulphate of magnesia -^^ do. 



5. Do — — ^V do. 



6. Muriate of magnesia ~ do. 



This 30th June 1806, the peas are not so thri- 

 ving in any of the pots as in Nos. 2 and 3, which 

 contained carbonate of magnesia, or the [common] 

 magnesia alba, of the shops. They are not so vi- 

 gorous in No. 2, which contained only jV of mag- 

 nesia, as in No. 3, which had }, where they are 

 more than a loot in length. This shews, that 

 magnesia is analogous to lime, in powerfully pro- 

 moting the growth of leguminous crops. 



The oats in No. 2 are taller, more vigorous, 

 and of a deeper green, than in No. 1. In No. 3, 

 they considerably surpass the two others in these 

 particulars. 



This clearly shews, that carbonate of magnesia 

 powerfully promotes the growth of oats and peas; 

 and that, in this particular case, the greater the 

 quantity applied, the more striking the eflect. 



Nos. 4, 5 and 6 remained long dormant, proba- 

 bly owing to an excessive dose of the magnesian 

 salts. The oats in No. 6 first began to spring; 

 and, though not so tall, are vigorous, and of a 

 lively deep green color. This shews, that though 

 muriate of magnesia may be applied in excess, it 

 is not in itself hurtful, but beneficial, to vegeta- 

 tion. 



The oats in No. 5 have lately begun to spring; 

 and those in No. 4 are now making a rapid pro- 

 gress. Their retardation does not shew that tiie 

 sulphate of magnesia is hurtful; but that too much 

 of it has been applied. 



I suppose earthy salts, especially those of mag- 

 nesia, operate chiefly by their strong septic power, 

 in promoting the putrefaction, and converting into 

 nourishment for plants, those animal and vegetabe 

 substances which exist in the soil. It is well 

 known, that sea-salt, which is much contaminated 

 with muriate of magnesia, instead of preserving, 

 promotes the putrefaction of meat, and especially 

 of fish. It is also probable these earthy salts 

 may promote vegetation, by their deliquescence 

 and attraction for moisture. This remark is par- 

 ticularly applicable to the muriate of magnesia, 

 whose plants are now making a very rapid pro- 

 gress, and the earth seems moist. 



But whatever errors we may commit in ac- 

 counting for the mode by which these substances 

 operate, I think the facts adduced clearly establish 

 this position, — That magnesia, and most, if not 

 all of its saline combinations, so far from being 

 hurtful, are beneficial to vegetation, if used in 

 due proportion. 



# * * » # 



JAMES HEADRICK. 



.Edinburgh, 30th June 1806. 



IV. 



Magnesia and JSIagnesian Limesiones. 



From Davy's Agricultural Chemistry. 



The subject of the application of the magnesian 

 limestone is one of great interest. 



It had been long known to farmers in the neigh- 

 borhood of Doncaster, that lime m.ade 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 contahied magnesia ; and on 

 mixing some calcined magnesia with soil, in which 

 he sowed difTerent 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 effects 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 employ 

 it advantageously in small quantities, seldom more 

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

 find it^ niay 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 for many months, 

 though exposed to the air. And as long as any 

 caustic lime remains, the magnesia cannot be com- 

 bined vTith carbonic acid, for lime instantly attracts 

 carbonic acid from magnesia. 



When a magnesian limestone is burnt, the mag- 

 nesia is deprived of carbonic acid much sooner than 

 the lime ; and if there is not much vegetable or 

 animal matter in the soil to supply by its decompo- 

 sition carbonic acid, the magnesia will remain for 

 a long time in the caustic slate ; and in this stale 

 acts as a poison to certain vegetables. And that 

 more magnesian lime may be used upon rich soils, 

 seems to be owing to the circumstance, that the 

 decomposition of the manure in them supplies car- 

 bonic acid. And magnesia in its mihl state, i. e. 

 fully combined with carbonic acid, seems to ])e 

 always a useful constituent of soils. I have thrown 

 carbonate of magnesia (procured by boiling the 

 solution of magnesia in super-carbonate of potassa) 

 upon grass, and upon growing wheat and barley, 

 so as to render the surface white; but the vegeta- 

 tion was not injured in the slightest degree. And 

 of one of the most fertile parts of 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 ex- 

 cellent mutton ; and the cultivated parts are 

 amongst the best corn lands in the county. 



That the theory which I have ventured to give 

 of the operation of magnesian lime is not unfounded, 

 is shewn by an experiment which I made expressly 

 for the purpose of determining the true nature of 



