1882,] COMMERCIAL FERTILIZERS. 73 



touched with acid at all, it makes a most serious difference whether 

 .the basis of the super-phosphate was bone or rock phosphate. 

 There is, then, safety in purchasing high-grade super-phosphates, 

 unless the buyer is perfectly satisfied with regard to the materials 

 used in a low-grade article, and the price justifies the purchase. 



"We come now to speak of the source of our supply of potash 

 fertilizers. 



Twenty-five years ago the potash used in the arts was derived 

 very largely from wood ashes. It was never applied in anything 

 like a pure state as a fertilizer. About that time, the constantly- 

 increasing demand and the very limited supply led to an investi- 

 gation of other sources of potash, and practicable methods were 

 devised for its extraction from orthoclase feldspar, which often 

 contains 16 per cent, of it in combination with silicic acid. 



These processes promised to help the difficulty somewhat, but 

 stiil the demand was in advance of the supply, and the market was 

 constantly rising, when, between 1860 and 1865, mines of potash 

 were opened and developed in Prussia, which instantly relieved 

 the want, made the production of potash from feldspar and wood 

 ashes unprofitable, opened the way for the establishment of a num- 

 ber of new industries, and made it possible and rational for the 

 farmer to apply potash salts in nearly a puie state to his land. 

 At present, the supply appears practically inexhaustible. 



In 1839, the scarcity of salt in Prussia (her salt springs fur- 

 nished only about three-quarters of the salt for home consump- 

 tion), and the geological formation in the neighborhood of Stass- 

 furt, led to exploration and boring, with the hope of striking salt 

 water, which could be economically handled for salt, or better yet, 

 rock-salt itself. 



In 1843, the first salt appeared, and in 1851 a salt-bed had been 

 penetrated for a thousand feet without reaching the bottom. The 

 boring had a total depth of nearly 1900 feet. The salt liquors 

 which were raised at first disappointed expectations, for they con- 

 tained comparatively little salt, but more of potash, and especially 

 magnesia compounds. 



A shaft was sunk, however, and at the depth of about 1,000 

 feet a bed of pure rock-salt was struck which is sufficient to meet 

 all demands for that article for untold years, and added greatly to 

 the wealth of the state. 



As time went on, however, it proved that, highly-prized as the 



