270 APPENDIX TO PART I. 



like the use of machinery in the arts, does not create anw^ 

 new power, but only tends to render more available those^ 

 already latent in the earth. 



"It was not therefore without reason, that Cato, after, 

 as we have seen, pronouncing, that the first, and the second 

 thing in agriculture, is to plough, adds, that the third is to 

 manure, for what is this but the art of providing for the in- 

 tended crop an adequate supply of those ingredients which 

 enter into its composition ? 



"The principles therefore which have been laid down, 

 whilst they will serve to guide the husbandman in the se- 

 lection of his fertilizers, may also explain the different re- 

 sults that are obtained from the use of the same kind of 

 mineral manure in different soils. 



" Among those which have excited the greatest interest 

 within the last few years, may be mentioned the nitrates of 

 potass, and of soda. 



"The former, commonly called saltpetre, is produced 

 spontaneously in most parts of the world, and especially in 

 hot countries, in consequence of animal and vegetable 

 decomposition conducted under particular conditions, and 

 accordingly it has been introduced into agriculture from an 

 early period.^ 



"The latter, sometimes distinguished from its crystalline 

 form, as cubic nitre, is met with in large quantities in Peru, 

 fourteen leagues from the port of Iquicque, where, ac- 

 cording to Mr. Darwin,! i^ forms a stratum two or three 

 feet thick, lying close beneath the surface, and following 

 the margin of a grand basin or plain, elevated 3300 feet 

 above the level of the Pacific, but which, nevertheless, 

 appears evidently to have been at one time a lake, or in- 

 land sea. 



"The price of the salt at the ship's side in 1835, at the 

 time Mr. Darwin visited the spot, was fourteen shillings a 

 cwt., the grand item of expense being its transport to the 

 coast. J 



K * Where the price operates as an objection to its use, the method 

 of forming artificial nitre-beds, by mixing together vegetable and ani- 

 mal matters in a state of decomposition with calcareous earth, may be 

 economically adopted. See Cuthbert Johnson, on Saltpetre and Ni- 

 trate of Soda, Ridgway, 1840." 



" t See Darwin's Journal, in Voyage of the Beagle." 

 i Mr. J. H. Blake of Boston, who recently visited Peru, informs me, 

 that the cost of the nitrate of soda was ^ 2.50 per quintal, and that it 

 could be obtained here at from 4^ to 5 cents per lb. The crude nitrate, 

 containing from 70 to 80 per cent, of the pure salt, might be obtained 

 here at 2^ cents per lb. — fV. 



