Ammonium Magnesium Phosphate of Analysis. 191 



salt present in the final precipitation increase. The quantity 

 of the ammonium salt present during the first precipitation 

 does not influence the error in the final precipitation unless it 

 is so large that a simple decantation of the supernatant liquid 

 would naturally leave an appreciable amount of it to act when 

 the second precipitation takes place. 









Table III. 









Mg 2 P 2 7 















corresponding 





Error in 



Error in 





HNaNH 4 PO 



t« 



to Mg(N0 3 ) 2 



Mg 2 P 2 7 



terms of 



terms of 



NH 4 01 



4H 2 







taken. 



found. 



Mg 2 P 2 7 . 



MgO. 



present. 



used. 



Volume. 





grm. 



grm. 



grm. 



grm. 

 A 



+ 0038 



grm. 



grm. 



cm 3 . 



( 1) 



0-5311 



0-5418 



+ 0-0107 







2-5 



150 



< 2) 



05311 



0-5462 



+ 0-0151 



+ 00057 



2 



(i 



150 



< 3) 



0-5311 



0-5408 



+ 0-0097 



+ 0035 



2 



" 



150 



(4) 



0-5311 



05500 



+ 0189 



+ 0-0068 



60 



" 



250 



( 5) 



0-5311 



0-5520 



+ 0-0209 



+ 00075 



60 



" 



250 



( 6) 



5311 



0-5345 



+ 0-0034 



+ 0-0012 



* 



» 



150 



( "0 



05311 



05371 



+ 0-0060 



+ 0-0022 



# 



t( 



150 



< «) 



0-5311 



0-5384 



+ 0-0073 



+ 0-0026 



* 



" 



150 



( 9) 



0-5311 



0-5386 



+ 0-0075 



+ 0-0027 



■* 



u 



150 



(10) 



0-5311 



05415 



+ 0-0104 



+ 0-0037 



* 



u 



150 



01) 



0-5311 



0-5312 



+ 0-0001 



+ 0-0000 



* 



u 



150,100 



(12) 



0-5311 



0-5311 



+ 0-0000 



+ 0-0000 



* 



" 



150,100 



(13) 



0-5311 



0-5346 



+ 0-0035 



+ 0-0013 



2 + 2 



" 



150,100 



(U) 



05311 



0-5348 



+ 0-0037 



+ 0-0014 



2 + 2 



" 



150,100 



(15) 



0-5311 



0-5383 



+ 0-0072 



+ 0-0026 



5 + 5 



(( 



150,100 



(16) 



0-5311 



0-5368 



+ 0-0057 



+ 0021 



5 + 5 



.; 



150,100 



(17) 



0-5311 



0-5376 



+ 0-0065 



+ 0-0023 



10 + 10 



" 



200,100 



(18) 



0-5311 



0-5395 



+ 0-0084 



+ 0-0030 



10 + 10 



it, 



200,100 



(19) 



0-5311 



0-5396 



+ 0-0085 



+ 0-0031 



60 + 5 



" 



250,100 



(20) 



0-5311 



0-5389 



+ 00078 



+ 0-0028 



60 + 5 



U 



250,100 



It is plain that the errors of excess which appear when 

 either the ammonium chloride or the soluble phosphate is 

 present in considerable amount, must be due either to mechan- 

 ical inclusion on the part of the highly crystalline precipitate, 

 or to variation in the ammonium magnesium phosphate from 

 the ideal constitution toward a condition represented by a 

 phosphate richer in ammonia and correspondingly deficient in 

 magnesium. If any appreciable amount of the ammonium 

 chloride present were held by the precipitate, it would natu- 

 rally be represented by magnesium chloride after ignition, but, 

 in no one of these experiments, even in those dealing with 

 sixty grams of ammonium chloride, did the residue, after dis- 

 solving in nitric acid, give with silver nitrate evidence of the 

 presence of more than a mere unweighable trace of chloride. 

 A special experiment, moreover, in which an attempt was 



* Probably less than 1 grm 



