374 



Nitrate of Soda as a Manure. 



require a good deal of practice to learn to ad just the proper bite ; they will 

 double the straw if too slack, and increase the draught when too tight. As ta 

 decrease of price I have not so favourable a report to give as one would 

 expect : the reduction is only 4/. — namely, to 38/. Mr. Crosskill's plea is, 

 that he was making the original implement almost at a loss. 



On the whole, however, I hope enough of successful progress has been 

 made to enable Mr, Crosskill to go on with confidence, and to satisfy the 

 agricultural community that a step has been made in following out the recom- 

 mendation of the Pusey judges without waiting a whole year. 



I should have liked to have seen the adoption of M'Cormick's knives, if 

 practicable, but as a medium between these and Hussey's I have hopes that 

 the present attachment to Bell's reaper will be found equally valuable with 

 the former. 



I remain, dear Sir, very faithfully yours. 

 To the President. Henry J. Hannam. 



XXIV. — On the Natural Law hy ivhich Nitrate of Soda, or Cubic 

 Saltpetre, acts as a Manure, and on its Substitution for Guano. 

 By the President. 



Though the plain path of practice is in agriculture generally the 

 safest, it will not be useless for that very practice sometimes to 

 deviate into theoretical considerations, the result .of vi^hich may 

 render the steps of experience more sure ; just as the sailor, while 

 buifeting with a stormy sea, ascertains his course by the abstruse 

 calculations of the astronomer. Such a field of inquiry is, I be- 

 lieve, presented to us in the use of saltpetre as a manure. 



This substance, or rather these substances — as there are twOy 

 the ordinary and the cubic saltpetre — consist of an acid, the 

 nitric acid, and an alkali, either potash or soda; nor could any 

 one, viewing the effect of these individual salts, decide whether 

 the acid or the alkalies were the source of their manuring action. 

 Looking, however, to the nature of other fertilizing matters, 

 I ventured, so long ago as the year 1841,* to express the belief 

 that their power would be found to reside, not in their alkalies, 

 but their acid. Still the arguments then adduced were not thought 

 conclusive, and in books subsequently published "f it was yet said 

 that the potash and the soda very probably were the manures, for 

 the mineral theory was still in vogue. 



Last year again, having some fresh facts to bring forward on 

 nitrate of soda, I endeavoured to support the same view by 

 showing further that other nitrates also, such as the nitrate of 

 lime found in old walls, have likewise a manuring effect. 



* Journal of Royal Agricultural Society, vol. ii. p. 123. 



t " Both Nitre and Nitrate of Soda are used as manures, and it is still uncertain 

 whether the acid of these salts contributes to the good effect, or whether they act 

 by their bases alone." — Outlines of Chemistry, by 0. Gregory, M.D. 



