96 



now readily obtainable in this country are kainit, sylvinit, muriate of 

 potash, high-grade sulphate of potash, and double sulphate of potash 

 and magnesia, or double manure salts. The kainit and sylvinit are 

 crude products of the mines, and contain, in addition to potash, a num- 

 ber of other salts, chiefly ordinary salt (sodium chlorid) and magnesium 

 sulphate. The potash in kainit, though in the form of a sulphate, pro- 

 duces an effect quite similar to thaf derived from the use of muriate, 

 because of the large quantities of chlorids mixed with it. It contains 

 on the average about 12J per cent of actual potash. Sylvinit differs 

 from kainit in con'aining a slightly higher per cent of potash, which 

 exists both in the form of a sulphate and of a chlorid, and a lower con- 

 tent of the magnesia and other salts. The other potash products men- 

 tioned are manufactured from the crude forms, and are much more con- 

 centrated. The muriate and sulphate contain on the average about 50 

 per cent of actual potash. The chief impurity in the case of the mu- 

 riate is common salt. The double sulphate of potash and magnesia con- 

 tains about 26 per cent of actual potash, though much lower grades of 

 this material are found. 



Materials that do not show a wide variation in composition, and in 

 which the constituents are practically uniform in their action, may be 

 regarded as standard in the sense that they can be depended upon to 

 furnish practically the same amount and form of the constituents wher- 

 ever secured. For example, a ton of nitrate of soda or boneblack super- 

 phosphates (dissolved boneblack) will on the average furnish 320 pounds 

 of nitrogen or of phosphoric acid, the nitrogen all in the form of a ni- 

 trate and the phosphoric acid practically all soluble ; whereas a ton of tank- 

 age, for instance, will vary widely both in the content and in the avail- 

 ability of its nitrogen and phosphoric acid, depending upon the method 

 by which it has been derived. Hence, nitrate of soda, sulphate of am- 

 monia, dried blood, and supeiphosphates and pofash salts are standard 

 products, because they can be depended upon both in respect to the con- 

 tent and form of their constituents. 



AGRICULTURAL V. COMMERCIAL VALUE OF FERTILIZERS. 



The agricultural value of any of the fertilizing constituents is mea- 

 sured by the value of the increase of the crop produced by its use, and 

 is, of course, a variable factor, depending upon (1) the availability of 

 the constituent, and (2) the value of the ciop produced. For example, 

 in the first case, the agricultural value of a pound of soluble phosphoric 

 acid is likely to be greater than that of a pound of insoluble when ap- 

 plied ur.der the same conditions as to soil and crop, because in the one 

 case the element is in its most available form, while in the other it is* 

 least available. In the second place, the soluble phosphoric acid may 

 exert its full effect and cause a greatly increased yield on a certain crop, 

 and still not cause an increase in value sufficient to pay the cost of the 

 application, while for another crop the application may result in a very 

 great increase in value. The character or form of the materials used 

 must, therefore, be carefully considered in the use of manures. Slow- 

 acting materials cannot be expected to give profitable returns, particu- 

 larly upon quick- growing crops, nor expensive materials such profitable 

 returns when used for crops of relatively low value as for crops of rela- 

 tively high value. 



This agricultural value is, however, separate and distinct from what 



