SOLUTION OF A MINERAL PHOSPHATE 28l 



with a greater quantity of accurately measured sulfuric acid than 

 is necessary for complete solution. The acid should have a 

 specific gravity of 1.455 or 45 B. The mixture is allowed to 

 stand for two hours at 50. It is then cooled, the flask filled 

 with water to the mark, well shaken, and the contents filtered. 

 Fifty cubic centimeters of the filtrate are treated with tenth-nor- 

 mal soda-lye, free of carbonate, until basic phosphate begins to 

 separate and becomes permanent after shaking. The excess of 

 acid is then calculated. Example : Twenty grams of phosphate 

 containing 28.3 per cent, of phosphoric acid, 10.0 per cent, of 

 calcium carbonate, 5.5 per cent, of calcium fluorid, and 2.4 per 

 cent, of calcium chlorid were treated as above with 16 cubic centi- 

 meters of sulfuric acid containing 10.24 grams of sulfur trioxid. 

 In titrating 50 cubic centimeters of the filtrate obtained as de- 

 scribed above, 10.4 cubic centimeters of tenth-normal soda-lye 

 were used, equivalent to 0.0416 gram of sulfur trioxid. Then 10.24 

 X5CH- 1000=0.5 i2O=total sulfur trioxid in 50 cubic centimeters 

 of the filtrate, and 0.5120 0.04160.4704 gram, the amount of 

 sulfur trioxid consumed in the decomposition. 



Therefore the sulfur trioxid required for decomposition is 

 47.04 per cent, of the weight of the phosphate employed. 

 One hundred parts of the phosphate would, therefore, require 

 47.04 parts of sulfur trioxid equal to 73.6 parts of sulfuric acid of 

 1.710 specific gravity or 92.1 parts of 1.530 specific gravity. 



A more convenient method than the one mentioned above, con - 

 sists in treating a small quantity of the phosphate, from one-half 

 to one kilogram, in the laboratory, or 50 kilograms in a lead 

 box just as would be practiced on a large scale. A few tests 

 with these small quantities, followed by drying and grinding, 

 will reveal to the skilled operator the approximate quantity and 

 strength of sulfuric acid to be used in each case. The quanti- 

 ties of sulfuric acid as determined by calculation from analyses 

 and by actual laboratory tests agree fairly well in most instances. 

 There is, however, sometimes a marked disagreement. The 

 general rule of practice is to use always an amount of sulfuric 

 acid sufficient to produce and maintain water-soluble phosphoric 

 acid in the fertilizer, but the sulfuric acid must not be used in 



