Preliminary consideration suggested a technique for studying the caking of granular fertilizers on a laboratory scale similar to that used in soil mechanics. An apparatus and technique were devised, and details of these are given. Time of storage of the fertilizer is found to be an important factor, and caking is rapid in the first few days. Preliminary investigations on the effect of chemical composition showed setting to be more serious when ammonium sulphate (I), superphosphate (2) and muriate of potash (3) were all present than when only (I) and (2), or (2) and (3) were included. Free acid content seemed to have little effect nor had light ammoniation of the superphosphate. Moisture content is related to caking, which has been reduced to negligible amounts by drying down to less than I% free moisture. Caking increases with the temperature, and this indicates the desirability of cooling. The correlation between the test developed and the results obtained on the large scale is discussed, and is shown to be sufficiently good for the test to be of considerable value.
The effects of acid concentration, acidlrock ratio, and fineness of grinding on the interaction between Moroccan phosphate rock and sulphuric acid, in the preparation of superphosphate, have been studied.An organic-solvent technique has been used t o follow the course and the rate of the chemical reactions. This method has been adopted because the precise composition of the superphosphate cannot be found by the analysis of water extracts, since interaction occurs between unchanged phosphate rock and free acids during the extraction.Results are given in the form of Tables and graphs.
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