74 Report of the commissioner of agriculture. 



oxide (KjO) tlicy can faniisli. The ])rincii>'U forms used are icood asJice, 

 in whicli the potash exists in variable amounts, chiefly as carbonate 

 (K2CO3); chloride of iioiasmim (KCl), commpnly known as "muriate of 

 potash," and sulphate of potassium (K0SQ4). 



These salts, when pure, contain the following amounts of potassium 

 oxide : y 



Per cent, of potash. 



Potassium carLonate contains 68. IG 



Potassium cliloricTe contains 6o.l7 



Potassium sulpliate contains 54.03 



The commercial salts are never imre, but an analysis showing their 

 content in potash serves to fix their value. Potassium carbonate is not 

 sold in the markets to any great extent except for soap-making. Applied 

 in moderate quantities in the form of wood-ashes, it is valuable, but 

 used in excess, it acts as a caustic injurious to plants. It is customary 

 to sell potassium oxide in the crude chloride ('• muriate") at a somevrhat 

 lower rate than it commands in the form of sulphate. There seems to be 

 two reasons for this discrimination: firstly, potas.siuto chloride can be 

 produced more cheaply ; secondly, it is strenuously held by some that 

 the effects of equal amounts of potash in the forms of chloride and sul- 

 phate are decidedly to the advantage of the sulphate. At the same 

 time the Connecticut Agricultural Experiment Station* has shown that 

 several of the much-praised sulphates were more properly chlorides. 

 Whether this preference for the sulphate is based upon facts or on 

 theory is certainly worth careful experimentation, that some definite 

 conclusions may be reached. 



III.— niosriioiiic acid. 



Phosphoric acid as such is not used, but it is supplied usually as a 

 phosphate of lime, either in ground and otherwise prepared bone or as a 

 superphosphate of lime prepared from bone, rock guanos, apatite, 

 rock i)hosphates, and phosphatic marls, such as those found abun- 

 dantly in South Carolina and other portions of this country. 



Phosphoric acid (or, more strictly, phosphoric oxide — P2O5) exists in 

 fertilizers in three conditions of very different commercial and agricult- 

 ural value. In the order of their value for fertilizing purposes they 

 are known as sohiUe, reverted, and insoluble iihosphoric acid. These 

 wiU be separately described: 



1. — Soluble pliosphoric add. 



This exists as an acid phosphate of lime (CaO.2H2O.P2O5), and is 

 formed by treating bones witli a proper quantity of sulphuric acid ("oil 

 of vitriol," H2SO4). This acid phosphate is fi^eely dissolved by water, 

 and has been proven to be more promptly useful than eitlier "reverted'^ 

 or ''insoluble" pho.sphates of lime. 



2. — Reverted phosphoric acid. 



This is also combined with lime, but in a different proportion. This 

 lime salt is represented by the symbol (2CaO, HzOPzOr,). Reverted 

 phosphate of lime results from a change that occurs upon long keeping 

 of tlie soluble pliosphate. It is not soluble to any appreciable extent 

 in water, but in the processes of analysis is dissolved in a .solu tion of 



" •Annual Report Conn. Agric. Exp. Sta., p. 37, (1879.) 



