ISO. 4.J MAXURIAL PROBLEMS. 151 



upon storing for a long time, some of the soluble i)hosphoric 

 acid of acid i)hosphate may change into a less valuable com- 

 bination than that of either dissolved bone or dissolved 

 bone-black ; but this is only the case when the acid })hos- 

 l)hate contains considerable quantities of iron and aluminum 

 oxides. On this account, the presence of large amounts of 

 these oxides in acid phosphate is to be avoided, unless the 

 phosphoric acid is nearly all " soluble," and even then unless 

 the goods are to be applied to the soil without material 

 delay. If acid phosi)liate is so strongly acidulated as to 

 render practically all of the phosphoric acid " soluble," it is 

 not likely to have as good an immediate effect or even after- 

 effect upon acid soil as when less strongl}^ acidulated ; and, 

 since dissolved bone is frequently less strongly acidulated 

 than acid phosi)hate, a better after-effect of the former upon 

 acid, unlimed soils may sometimes result. The lesson from 

 this should be to lime such soils, and not necessarily to 

 employ dissolved bone instead of acid phosphate unless the 

 relative prices justify it. 



Concerning "reverted" phosi)horic acid, recent experi- 

 ments at Kingston indicate that it has a widely varying 

 value, dependent (1) upon the materials which furnish it, 

 (2) upon the kind of crop that is grown, and (3) upon the 

 kind of soil to which it is applied. Unfortunately, the 

 official chemist in analj^zing fertilizers cannot take into 

 account the two latter factors in reporting upon the value of 

 their phosphoric acid. As the analyses are made to-day, the 

 official chemists of none of the States take into account, in 

 reporting the reverted phosphoric acid, the source from 

 which it is derived ; and the consumer of fertilizers is led to 

 think that the reverted phosphoric acid in all fertilizers is 

 equally valuable. In fact, it is probable that the reverted 

 phosphoric acid shown by the ordinary official methods of 

 analysis to be present in bone or tankage on the one hand, 

 and in dissolved bone-black and dissolved bone on the other, 

 is not equally valuable for immediate plant production, the 

 preference being given to the latter two substances. Any 

 discrepancy in value in these materials fades, however, into 

 insignificance as compared with that which appears between 



