Philosophy of Manures. 337 



and applied so successfully lately by Mr. M'Intosh at Dalkeith, 

 owed their effect to the ammonia ; which by the smell given off 

 banished the insects, and, being absorbed by the roots, increased 

 the vigour of the plants. I have lately seen powerful effects 

 produced on onions, by sifting soot (a similar substance) on 

 the beds in wet weather. In some instances, where the soot 

 had not sufficed to go over the whole, the precise spot where 

 the sifting stopped could be pointed out, by the plants that 

 had got none being at least one third less in bulk.* The car- 

 bonate of ammonia, therefore, though very volatile, if judiciously 

 managed, should be a very safe and powerful manure; and it 

 may be preserved in liquid manures by keeping them cool, or by 

 adding loam or charcoal powder where this cannot be done, to 

 absorb and retain the ammonia, and give it out again to the 

 water of the soil. The method advised by Professor Johnstone, 

 to dilute these manures in great quantities of water, and apply 

 at different periods of the growth of the plant, points out the true 

 theory of their action. Ammonia, Professor Daubeny says, in 

 its caustic state, or unencumbered with acids, will kill plants, if 

 confined in the air they are growing in, in the proportion of 1 

 part in 100; hence we see the poisonous nature of fresh unfer- 

 mented urine, unless very much diluted : when allowed to ferment, 

 the free ammonia is mostly converted into carbonate, and not so 

 dangerous unless in excess. The ammonia of the sulphates and 

 muriates should, when decomposed, as they must be in the 

 plant, liberate the ammonia in a free state, till again neutralised 

 by the carbonic acid of the plant, and be a further source of 

 danger in employing those maniu'es, viz. ammonia united to 

 mineral acids in large quanlities. 



On the necessity of INitrogen, as affecting the strength of plants 

 and animals, I have seen families of Irish labourers in this town, 

 who, I was informed, made their sole food to consist of potatoes 

 and salt three times a day, and, though not so large and weighty 

 as those fed on more stimulating food, were healthy active men. 

 This food, I have been informed, is more exclusively prevalent 

 in the inland districts of Ireland. The stimulating qualities of 

 nitroiien seem, therefore, more conducive to bulk than better 



* All soots, however, are not beneficial. Having lately recommended soot 

 as a dressing for onions to a friend in Stranraer, he said any time this had 

 been done the whole crop had been destroyed. Peats are generally used 

 there for fuel ; and though the bog they are cut from is two miles from the 

 sea, yet the ground slopes to it ; and so great is the quantity of sea salt accu- 

 mulated, that, where these peats are burned in cottages imperfectly finished, 

 the soot collects on the joists, couples, rafters, and other wood-work of the 

 house ; and, in wet weather, so great is the quantity of salt contained in the 

 soot, that it deliquesces with the moisture (not rain) of the air, and drops in 

 salt (not acid) globules of water. This should convince those who have so 

 frequently denied that salt is carried to any distance inland. 



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