28 USE OF FELDSPATHIC ROCKS AS FERTILIZEES. 



pound of feldspar in different degrees of subdivision. First, in the 

 form of a solid cube, then broken down to particles that could just 

 pass an 80 and a 200 mesh sieve, respectively, and, finalh^, in the con- 

 dition it would be if it were possible to grind all the material as 

 fine as the finest particles which occur in an ordinary 200-mesh 

 powder. The 1 pound of feldspar in a solid cube would have a sur- 

 face area of 29.3 square inches; particles capable of passing an 80- 

 mesh sieve would giA'e 8,870 square inches; particles able to pass a 

 200-mesh sieve would give 24,905 square inches; and if it were pos- 

 sible to reduce the powder "to particles 0.0001 millimeter in diameter, 

 there would result a surface area of 16,460,000 square inches. 



If it wei^e practically possible to collect 1 ton of feldspar all in the 

 state of the finest particles, as shown above, the surface area pre- 

 sented by the ton would be enormous — in fact, it would be equal to 

 256,000,000 square feet, 5.877 acres, or more than 9 square miles. 

 Now, although such grinding is out of the question at the present 

 time, an ordinary 200-mesh feldspar prepared for the pottery trade, 

 which is valued at about $8 per ton, contains a large proportion of 

 very fine particles. The marvelous rise in the surface area attained 

 by fine grinding is very well exhibited in the figures given, and it is 

 undoubtedly true that previous experimenters have not paid sufficient 

 attention to the percentage of very fine material in the ground feld- 

 sjjar. 



One opponent of the use of feldspar has written : " 



What we call soil is roelv of various sorts criislied or broken up by weather 

 aud other agencies. The crushed grauite could hardly be more fertile tU^ii a 

 good soil. Wheu we thiuk that an acre of soil 1 foot deep weighs over 3,500.000 

 pounds, we see what a drop in the bucket a few tons of ground rock really 

 amounts to. 



As a matter of fact, discussion of the value of a few tons of fine- 

 ground potash-bearing rock, with its millions of square feet of sur- 

 face area, can not be so easily brushed aside. It is true that the soil 

 contains man}' fine particles; but those Avhich, like feldspar, suffer 

 decomposition under the action of water have presumably been 

 already decomposed, and this new material is to replace that which 

 has been used up or removed. Each tiny particle of feldspar pro- 

 vides only a small increment of potash, but in a ton of fine-ground 

 material there are many billions of particles. 



COST OF GROUND FELDSPAR. 



Nearly all of the feldspar which is at present ground to fine pow- 

 ders is prepared, as has been stated, for the pottery trade. For this 

 purpose it is necessary to use mills with specially adapted linings so 



a The Potash in Crushed Rock, German Kali Works, New York. 

 104 



