J. F. Tocher 141 



law of mass action we should expect k = ujw — 2m to describe the ex- 

 perimental results. An inspection of col. Ill (Table X) will show that 

 the formula reasonably fits the data. No account has been taken of the 

 degree of ionisation in the above equilibrium equation. The extent of 

 the reverse action, 



CaH,(P04).l;CaHP0, + H3PO4, 

 has also been neglected. 



If the degree of ionisation of liydrochloric acid is taken into account 

 together with the fact that a minute Cjuantity of calcium hydroxide was 

 found to be present in the dicalcium phosphate used it is found that 2m 

 is slightly greater than hi as may be seen on inspection of Table XI 

 (col. IV). The value of 'liijw varies from 1-008 to 1-039, the average 

 value being 1-0228 and theory requires this ratio to be equal to unity 

 for a completed reaction. 



Table XI. 



The work in this section is intended merely to illustrate the approxi- 

 mation to a completed reaction in the case of a known phosphate. More 

 detailed work is necessary and a fuller con.sideration of the theory is also 

 necessary in order to give a complete physico-chemical explanation of 

 the phenomena. 



IX. f«i\CLUSIO\S. 



(1) If constant weights of sample and of citric acid are used in a 

 series of experiments, the only quantity varied being the volume, the 

 quantity of phosphate dissolved per cent, of weight of sample taken 

 increases with increasing volumes. With 5 grams of sample and 10 grams 

 of citric acid, the citric solubihty varied from 19-24 to 28-14 per cent, of 

 weight of sample. With 1 gram of sample and 10 grams of citric acid, 

 the citric solubihty varied with increasing dilution from 53-8 to 61-8 per 

 cent, of weight of sample. The effect of the presence of alkahne lime was 

 ehminated by maintaining mjm^ at a constant value and with increasing 

 dissociation as a result of increasing dilution increasing percentages of 



