2o6 SOLUBILITY OF lUIOSPHORlC dXIDK. 



over 14I/2 per cent, in two weeks. In Gray's experiment only 

 3 per cent, of the soluble ])hosphoric oxide reverted. 



In a further experiment bone ash (CagPoOg) was used, 

 which was found to contain .74 per cent, of soluble phosphoric 

 oxide.* The superphosphate was the same as previously used, 

 analysino- 19.37 P^^" t-^ent. of water-soluble phosphoric oxide. 



This mixture (equal parts of bone ash and superphosphate) 

 gave the following- percentages of water-soluble phosphoric 

 oxide at the end of the times stated: 



The tigures obtained from the first two determinations were 

 rather surprising, and as they might possibly have been due to 

 improper mixing, a further independent mixture was made, 

 which analysed 12.14 and 12.09 'ifter standing for 3 and 24 

 hours respectively. 



This increa.se was plainly due to the presence of free acid 

 in the superpho.sphates used in the above set of experiments, or. 

 in other words, there was enough free acid in the superphosphate 

 used to bring about solution of the 2.00 per cent, of phosphoric 

 oxide by which the original 10.05 P^'^' ^"ent. was increased. In 

 order t(') confirm this a solution of a superphosphate was made 

 as follows : 100 grams \vcre extracted for half an hour with 

 distilled water in a 1 .000 c.c. flask, shaken in a shaking apparatus 

 for half an hour, filled up to the mark, and an aliquot ])art of 

 the filtrate gave a result e(|uivalent to 18.92 per cent, of water- 

 soluble phosphoric oxide in the superphosphate. To 500 c.c. of 

 the clear filtrate. ec|uivalent to 50 grams of superphosphate 

 3.35 grams of inire precipitated tricalcium phosphate were 

 added, and tlic mixture extracted in a shaking apparatus for 

 half an iK.ur. tilled up to the 1,000 c.c. mark, well mixed and 

 filtered. In an aliquot ])art the water-soluble phosphoric oxide 

 was found to be e(|uivalent to 19.84 per cent., again proving that 

 in the mixture- of superi)hosi)hate and bone asli an increase in the 

 water-soluble phosi)horic oxide results. 



A blank determination of the water-soluble phosphoric oxide 

 in the ((uantity (jf preci])itate(l tricalcium phosphate actually used 

 was found to yield 0.064 gram of water-soluble i>hosphoric oxide. 



Calculaled amount in a Mixture C)f rci-renlaf4C fcnuid in a Mixture of 



100 (jranis i)f Superphosphate lOoGrams of Superphosphate and 



and 6.70 (Iranis of Precipitate*! ('.70 Grams of Precipitated Tri- 



Tricalcium I'Iiosi)liate. calcium Phosphate after Shaking. 



l7.tjO per rent. 19-84 l)er cent. 



.■\ further test, n.sing S(.)nie specially pre])ared C"a.,P.X)„ from 

 KahlbauuL containing 0.025(1 gram of water-.soluble phosphoric 

 oxide. ga\e the following results: — 



*A flui)Iicate deU-rmination liave .73 per cent. 



