rilOSPIIOEIC OXIDE IN FERTILISERS. 27-^) 



The first three mixtures, namely, superphosphate with 

 mineral phosphates and limestone, should })& looked upon 

 as more of a scientific nature, as such mixtures are not likely 

 to find favour with farmers; yet, nevertheless, like mixtures 

 have been recommended from time to time. 



The result of a number of trials with a mixture of 

 two parts of superphosphate (IG per cent, water-soluble 

 phosphoiic oxide) and one part of Tunisian phosphate are 

 g'iven in the January number of the " Journal of the 13epai*t- 

 ment of Agriculture and Technical Instruction for Ireland." 

 This mixture, when applied at the rate of 3 to G CAvt. 

 per acre, had given favourable results with potatoes, 

 mang'olds, turni}>s and hay as compared Avitli a similar diessing 

 of superphosphate. 



The Tunisian ])hos])hate itself, according' to the report, 

 has given good returns, tilthough slightly inferior to super- 

 phosphate; but the fact must be borne in mind that the/ 

 residual value Avill be greater in the case of the untreated 

 mineral phosphate than that of superphosphate. The same 

 remark would apply when a mixture of superphosphate and 

 mineral phosphate is applied. Professor Gilchrist, at Cockle 

 Park, 1915, also reported favourably on a mixture of super- 

 phosphate and mineral phosphate over a three years' trial. 



In the case of supeiphosi;)hate and Ephos basic phosphate 

 (treated phosphate by chemical fusion), the amount of 

 reversion is gradual. At the end of three weeks it is under 

 20 per pent. When, however, attention is drawn to a mixture 

 of a somewhat similar nature, namely, superphosphate and 

 basic slag, the leversion takes place at a very rapid rate, and 

 when calculated approximately to a period of little over 

 three weeks there is a loss of Avater-solu])]e phosphoric oxide 

 to the extent of about 79 per cent. The great difference 

 between two such mixtures is probably due to the fact that 

 basic slag contains a higher percentage of caustic lime than 

 Ephos basic phosphate. Gray, in a set of experiments using 

 slaked lime, found that the rate of leversion was particularly 

 rapid, 94 per cent, of the water-soluble phosphoric oxide being- 

 reduced within three hours, and tlie whole amount present 

 within twenty-four hours. 



In a mixture of superjjhosphate and Saldanha Bay 

 phosphate, which consists almost entirely of iron and alumina 

 phosphate, with a trace of lime combined as carbonate, one 

 would expect the loss in water-soluble phosphoric oxide to be 

 great, yet the results prove that the rate of reversion is 

 gradual, and at the end of a period of three weeks it is 

 approximately only 11 per cent. In the case of superphosphate 

 and Gafsa phosphate (a IS'orth African phosphate), although 

 quoted by Robertson as probably being the most suitable for 

 mixing with superphosphate, there is a reversion of about 

 22 per cent, when calculated on a period of little over 

 three weeks. 



It_ is evident from results of mixtures such as above 

 there is no apparent gain to the farming communitv to 



