On Trihasic Phosphoric Acid. 181 



In heating (a), at 100° C. 



For 2 hours=15.18 p. c. 

 " 3 " =15.31 p. c. 

 « 16 " =20.85 p. c. 

 Part of the water, therefore, seems to be retained by a 

 stronger affinity than the rest. 



II. Determination of the iron loith permanganate of potassa. 



The reduction of the iron was effected in a wide-mouthed 8 

 oz. bottle, which was covered with a glass plate. The hydro- 

 gen acted on the sesquioxide from a piece of platinum, that 

 was in the acidulated fluid, touching a piece of amalgamated 

 zinc. The reduction was finished in about twelve hours, with- 

 out the slightest trouble or inconvenience. 



Hydrochloric acid, in these experiments, giving me always 

 differing results, I dissolved the aforesaid powder in sulphuric 

 acid and then titered. Those differences, by the way, were the 

 cause of my trying the various methods of determining iron by 

 "weight and measure. The permanganate solution indicated 

 in the cubic centimetre 0.0065 srr. metallic iron. 



CD 



The results are as follows : 



(a) 0.3886 gr. = 13.90 c. c. = 33.21 p. c. Fe,O s 



(b) 0.3168 " =11.40 c. c. = 33.41 p. c. " 



(c) 1.0852 " =38.80 c. c.=33.20 p. c. " 

 mean = 33.27 p. c. 



The salt was therefore composed of 



36.76 P0 6 (by loss). 

 33.27 Fe a O, 

 29.97 HO. 

 Corresponding to the formula: 



Fe, 0,4, PO, 5+ IK) 32, 

 or perhaps, as a part of the water is driven off more easily 

 than the rest, of 



5 (Fe 2 3 2, PO. 3 + 8 HO) +2 (Fe, 0„ 3 BO) 4 50 HO. 



