16 On the Theory of Manures. 



ferent situations. This has been ascribed to the places in which 

 it failed being near the sea coast ; and, the lands abounding in 

 salt (muriate of soda or chloride of sodium), they had therefore 

 no need, it is said, for nitrate of soda, and hence the want of 

 effect. At E-oselle, which is so near the sea as to entitle it to 

 the benefit of a saline atmosphere, and where common salt was 

 found to jDroduce no effect which might be ascribed to that cause, 

 nitrate of soda was found to produce a powerful one. Yet 

 even here it was found by the gardener that a small quantity 

 killed the stool plants of sea-kale, while, at the Society's Experi- 

 mental Gardens, it has been given in doses of 1 lb. to the plant 

 with good effect. The nitric acid of the nitrate when absorbed 

 must have a different effect from the muriatic acid or chlorine of 

 the other. The latter are seldom found as constituents in plants, 

 and little is known of their beneficial action ; while nitric acid has 

 been found by Braconnot to produce fibre from starch, and, if 

 confirmed by further experience, may be found in this way to 

 assist in j)erforming an important part in the vegetable economy. 

 It is also said to assist in the formation of oxalic acid, which 

 last is thought to abound more in plants than analysis points 

 out ; the oxalate of potash being changed into a carbonate in 

 extracting it. Like ammonia, nitric acid probably assists also, 

 by the nitrogen it contains acting as a stimulus to growth : pro- 

 bably ammonia is formed from it, as it is generally found to give 

 rise to a dark green colour, denoting the alkaline state of the 

 chromule, an appearance which generally betokens vigour of 

 growth, but is sometimes found to appear without this increase. 

 When a sufficient dose of manure has been given before the 

 dressing of nitrates, they have been often found to produce no 

 additional effect. At Cajarington this season, a lot of potatoes 

 had been manured at the rate of about fifty cubic yards of 

 well rotted manure (about thirty tons), and the crop produced 

 was about twenty tons per acre, the manure and working of 

 the land being excellent : but some drills, dressed with the usual 

 quantities of nitrate of soda, suljjhate of soda, and urate con- 

 taining a great deal of ammonia, had no perceptible increase; 

 apparently from the large quantity of ammonia supplied by 

 the manure to a crop not carrying off much nitrogen, the 

 substances containing it had no effect. Some nitrate of soda 

 and sulphate of soda, sprinkled on a crop of vetches in an 

 adjoining field, caused a great increase of produce, showing 

 that there was nothing naturally in the soil against their acting. 

 The many causes noticed in the commencement of this essay 

 may have occasioned different results, and may not have been 

 observed. Sometimes the substances lie over year in cold 

 soils and cold seasons before producing effect ; and some may 

 have been applied unwittingly to pieces of fields which were 



