MANURES AXD MANl^RIXO 



Q49 



time is spent on the extraction. The phosphate or phosphates which the 

 slag contains do not appear to be in combination with siUca and thej^ seem 

 to bear a very close resemblance to those contained in mineral phosphates. 



At the present time there is a very big demand for phosphatic manures, 

 and if temporary difficulties, such as a lack of railway facilities and shortage 

 of bags, could be to some extent mitigated there is no reason why these 

 low citric soluble basic slags should not be placed on the agricultural market 

 at a tempting price (i). 



II. — The citric solubility of several classes of mineral phosphates has 

 been determined and also the effect, upon the solubility of the phosphate, 

 ot fineness of grinding and calcining. 



Phosphoric 



acid 

 dissolved. 



Citric Solubility of Rock Phosphates. 



j3 y 



ii > 

 ■P "55 

 a. 





13 § 



S " ''O 



1-23. 



fa •°- 



O. o 



ffi °' 



i!2 * BC 



t- £i 



°^'0 



= > 

 -o 2 



a - 



o be 



d .2 



ist extraction . 



ind extraction . 



3rd extraction . 



4th extraction . 



5th extraction . 

 Total extract 

 Actual total . 



1 P^' i 

 I cent 



' 3-93 

 3.66 



3-47 

 3.28 

 2.91 



!i7.25 

 jS.go 



per 

 cent 



per 

 cent 



per 

 cent 



per 

 cent 



9.25I 6.581 4.OO; 6.18 



8.261 6.32 3.S1 5.83 



7-54J 5-55 3-63 546 



6.03 4.63 3.23' 5.14 



4.22 3.79 



3.00J 4.31 



35.30 26. 87117.67126. 92 

 38.2438.2433.27 31.50 



per 1 

 cent I 



6.0li 



6-77; 

 6.63i 



5-41^ 

 3.88I 



28.78! 



3i-5o\ 



per 

 cent 



per 

 cent 



per 

 cent 



per j per 



— " ' cent 



6-65: 3.33 10.15 

 6.48 4.361 8.18 

 5-35J 3-78; 560 

 4.00J 3.10: 1.93 

 2.47 2.29' — 

 25.45 16.86i25.86 

 27.27 27.27 25.35 



cent 



5.20 



6-55 



5-77 



4-49 



1-95 

 5-65 

 578 

 4-95 



2.29 1.99 

 24-3030-32 

 25351980 



per 

 cent 



7.80 



6.98 



6.20 



4-53 



3.08 



46.52 



50-55 



* Free lime removed by sugar solution. 



The results undoubtedly show that mineral phosphates are comple- 

 tely soluble in 2 % citric acid if a sufficient number of extracts are made. 

 In the majority of the rock phosphates examined five extracts removed 90- 

 100 "^0 of the phosphoric acid present. 



Even a small amount of free lime or calcium carbonate decreases 

 sub.stantially the solubility of mineral phosphates as judged by the citric 

 acid test. When a large amount of calcium carbonate or free lime is pre- 

 sent, the citric acid test, as commonly practised, is a test for lime and not 

 for phosphates. It is important in this respect to distinguish between free 

 lime and calcium carbonate, and lime actually entering into the composi- 



(i) See B. Aug. IMI5, Xn. 706 : also B. 

 B. Feb. i'ji6, Xo. i4(). 



Oct. 1915, Xo. jKio ; li . 



Jan. 1916, No. 147 'intl 



[Ed.]. 



