374 Dr. Griffith on theAmmonio-magnesian Phosphates of the Urine. 



and not unfrequently, in a somewhat modified form, in acid 

 urine, and is called the neutral phosphate of ammonia and mag- 

 nesia. These forms are both figured in my " Practical Manual," 

 &c, 1843, and in most other works on animal chemistry ; but 

 their respective compositions have not, so far as I am aware, 

 been determined, nor the connexion of the forms with the com- 

 position been ascertained. A knowledge of this deficiency in- 

 duced me in 1845 to prepare artificially and analyse the bibasic 

 or stellate form, which can be readily procured, and in a tole- 

 rable state of purity, from healthy urine. This analysis was 

 published in the second part of my Manual, p. 58, and shows 

 that this phosphate agrees in composition with that prepared 

 artificially and analysed by Professor Graham*. The difficulty 

 in determining the constitution of the neutral salt, as it is called, 

 has depended upon the constancy with which it occurs mixed 

 with either the basic salt, or mucus and other foreign substances. 

 I lately, however, found a method of preparing it, in a tolerably 

 pui'e state, from healthy urine, as from an artificial saline mixture. 

 If healthy urine be diluted with water, and very dilute solution 

 of ammonia be stirred into it in small quantities at a time, taking 

 care that its acidity be not completely neutralized, the so-called 

 neutral triple phosphate will be thrown down. It is also formed 

 when dilute solution of ammonia is added to a dilute aqueous 

 solution of phosphate of ammonia and sulphate of magnesia. 

 The precipitates in both cases consist of prisms exhibiting all 

 the forms of the neutral phosphate met with in animal fluids, 

 sometimes grouped, at others isolated, and the forms are identical 

 in both cases. 



After washing the crystals with cold water, they were allowed 

 to dry in the air, and analysed in the usual way. The compo- 

 sition of this ' ' neutral " salt was then found to be identical with 

 that of the "bibasic;" thus — 



I. II. III. 



NH 3 . 17 ' 693 7-32 



2MgO . 40 16-301 4 KM AKfK AK11 f 16-47 



PO> . . 71-4 29-09 j 45 ' 39 45v6 45 ' 73 129-26 

 13HO 



The conditions under which these two forms acquire their 

 different crystalline figures appear to be these. The ammonio- 

 phosphate of magnesia is less soluble in solution of ammonia 

 than in water or urine. Hence when only just sufficient am- 

 monia is present to form the ammonio-phosphate with the 

 phosphate of magnesia in solution, the crystals are slowly pro- 

 * Trans. Royal Soc. of Lond. 1837, p. 68. 



