176 THE SECRETIONS: 



amorphous mass, in which large, well-defined globules, some- 

 times united two and two, are often observed. Fig. 28 a and 

 b exhibit these forms. It is obvious from a comparison of fig. 

 28 a, and fig. 26, that the urate of ammonia, in consequence 

 of its form, may easily be mistaken for phosphate of lime. The 

 following points enable us to distinguish them. Phosphate of 

 lime occurs as a sediment only in neutral and alkaline, never 

 in acid urine. Phosphate of lime when examined under the 

 microscope disappears instantaneously on the addition of a 

 little hydrochloric acid, which usually develops numerous air- 

 bubbles. The sediment of urate of ammonia does not disappear 

 so rapidly under similar treatment, and in a short time, fre- 

 quently only a few minutes, its place is occupied by rhombic 

 crystals of uric acid, as shown in fig. 28 c. 



The quantitative determination of urate of ammonia pre- 

 sents no difficulty when no other constituent is present in the 

 sediment. The weight of the urine and the amount of solid re- 

 sidue are accurately determined : the sediment is collected in 

 a filter of known weight, washed with a little ice-cold water, 

 dried, and weighed. The ratios of the amount of sediment to 

 that of the whole urine, and to that of the solid residue are thus 

 obtained. In order to separate the urate of ammonia from uric 

 acid, earthy phosphates, or mucus, with which it may be mixed, 

 the sediment must be collected, and the quantity of urine 

 from which it was deposited, carefully ascertained. The sedi- 

 ment must then be placed in a test-tube with a little of the 

 urine, and gradually raised to the boiling point (if we are pre- 

 viously assured that no albumen is present) : it must then be 

 filtered, and the residue washed with a little hot water, while the 

 clear fluid that passes through the filter must be artificially 

 cooled, and the urate of ammonia allowed to separate. It 

 must be collected on a filter, dried, weighed, and its ratio de- 

 termined in reference to the urine, and to the solid residue. 

 The determination of the urate of ammonia as uric acid, from 

 which the amount of the salt might be calculated would, per- 

 haps, give safer results, since uric acid is less soluble than urate 

 of ammonia. 



The fluid which, by the application of heat, has taken up the 

 urate of ammonia from the mixed sediment, must be concen- 

 trated by evaporation, and treated while still warm with hydro- 



