264 BOARD OF AGRICULTURE. 



citrate, and includes not only the trnl}' reverted, but also more or 

 less of i)hosphoric acid a« combineil in the original, undissolved 

 phosphatic material. Reverted phosphoric acid, in so far as it comes 

 wilhin the strict meaning of the term, most probably has a value for 

 crop production equal to that of the soluble form, but it is not clear 

 that this holds true of that which would be dissolved by ammonium 

 citrate from iinely ground South Carolina rock, for instance, at a 

 temperature of G5° C. 



Insoluble phosphoric acid is that which is readily soluI)le neither in 

 water nor in a solution of ammonium citrate, but which can be dis- 

 solved in strong acids. It comes from some of the original phosphatic 

 material that has not been acted upon by sulphuric acid, and depends 

 somewhat for its value upon the kind of material used, whether 

 bone or rock phosphate. In any case it has less value than the 

 soluble or reverted forms. 



It should be remembered that the terms "soluble," "reverted," 

 and "insoluble" are merelv relative in their siornificance. There is 

 no compound of phosphoric acid that is not dissolved to a slight 

 extent, at least, by pure water, and to a still greater degree by 

 ammonium citrate, and the extent of the solubilit}^ of raw phosphates 

 in these liquids, and in weak acids such as are found in the roots of 

 plants, depends very largely upon their mechanical condition, or the 

 degree of iineness to which thev are ground. 



The potash used in this country for agricultural purposes comes 

 mostl}' from German}' in the so-called "German potash salts," which 

 include potassium sulphate, potassium chloride (the muriate) and 

 kainite. Except for a few special purposes, potash is equally valu- 

 able in all these forms, but costs least in the muriate and in kainite. 



The Valuation of Fertilizers. 



The law establishing the Station requires that the average of three 

 analyses of each brand of fertilizer sold in the State, with certain 

 exceptions, shall lie compared with the guaranteed composition of 

 the fertilizers examined. 



This Station, in common with all American experiment stations 

 that stand in an official relation to the fertilizer trade, goes farther 

 than this and applies a schedule of trade values to the goods that it 

 inspects. By means of these trade values there is calculated for 

 each brand what has been designated as the "estimated value" or 

 the "station valuation." As these estimated values are not intended 



