Mr. Maddrell on the Metaphosphates. 323 



phosphate of magnesia ; and it was not until after a third re- 

 petition of this process that I obtained Professor Gregory^s 

 compound, in which I found on analysis 16-276 per cent, of 

 magnesia, corresponding to the quantity found by that che- 

 mist in his salt ; but on estimating the quantity of phosphoric 

 acid present, I only obtained 75-25 per cent, of PO5, leaving 

 a loss of upwards of 8 per cent. Being convinced that an- 

 other base must be present, fi-om the enormous loss, I pro- 

 ceeded further with my analysis and found the presence of 

 soda, which gave me 8-146 per cent, of soda. 



This salt therefore is not an anomalous phosphate of mag- 

 nesia, but a double metaphosphate of magnesia and soda, in 

 the proportions are 3 equivs. of metaphosphate of magnesia 

 and 1 equiv. of metaphosphate of soda, 3(MgO, PO5) 4-NaO, 

 PO5. It is nearly insoluble in hydrochloric acid and aqua 

 regia, but soluble in concentrated sulphuric acid. 



The analysis of the salt was made as follows : — I dissolved 

 the salt in pure concentrated sulphm-ic acid, then diluted the 

 solution with water, and precipitated the magnesia by an ex- 

 cess of ammonia ; from the precipitate, after being heated to 

 redness, was estimated the quantity of magnesia. To the fil- 

 tered solution was added a solution of a salt of magnesia (with 

 proper precautions) to precipitate the remainder of the phos- 

 phoric acid, and from this precipitate, as well as the former, 

 was estimated the quantity of the PO5. A second quantity 

 was taken for the determination of the soda, which was dis- 

 solved in concentrated sulphuric acid, diluted with water, and 

 precipitated by an excess of ammonia. The filtered solution, 

 containing pliosphoric acid, was then precipitated by acetate 

 of lead, the excess of lead by sulphuretted hydrogen, and the 

 soda in the solution evaporated and estimated as a sulphate, 

 which gave me the following results : — 



Analysis, No. I. p^^. ^^,,j^ 



•897 grm. substance gave -399 2MgO, POs -146 MgO = 16-27(J MgO 



•897 1065 ... -675 POs = 75-250 POg 



•712 -133 NaO SO3 -058 NaO = 8-146 NaO 



99-672 



No.n. Percent. 



1-16 grm. substance gave -511 2MgO, POj = -187 MgO = 16-12 MgO 



1-16 1-386 ... =-878P05 = 75-689 POfi 



1-23 -228 NaO, SO3 =-099 NaO = 8-018 NaO 



99-857 



Z2 



