174 THE SECRETIONS: 



The alkaline solution must be filtered, and the uric acid 

 precipitated by hydrochloric acid, collected on a filter, dried, 

 and its weight ascertained. We thus estimate the ratio of the 

 separated uric acid to the whole fluid and to the solid residue, 

 if indeed this element has been determined from a weighed 

 quantity of the urine. A certain quantity of the urine is 

 treated with hydrochloric acid in the manner indicated in page 

 137, allowed to rest for twenty-four to forty-eight hours, and the 

 precipitated uric acid collected on a filter and weighed. We thus 

 obtain the amount of uric acid held in solution, and its ratio 

 both to the whole amount of urine, and to the solid residue. 



b. Increase of urate of ammonia. Urate of ammonia, which, 

 as we have already mentioned in page 115, is probably an inva- 

 riable constituent of urine, is occasionally excreted to a very 

 large amount during the exacerbations of fever, arthritic attacks 

 and various other diseases. It is the most common form of 

 urinary deposit, but seldom occurs alone; it is frequently mixed 

 with uric acid, sometimes with urate of soda or of lime, and 

 occasionally, but not often, with earthy phosphates. Urine 

 depositing urate of ammonia is generally of dark colour, is 

 seldom clear, and usually exhibits an acid reaction ; it is, how- 

 ever, occasionally neutral or even alkaline. It is only in the 

 latter case that earthy phosphates can be present, as they are 

 never precipitated in urine with a marked acid reaction. The 

 colour of urate-of-ammonia sediments varies from a yellowish 

 to a brick-red tint. The red sediments frequently contain free 

 uric acid, and sometimes urate of soda ; nearly white sediments 

 of urate of ammonia have occasionally been observed. Urate 

 of ammonia seems to preponderate in the yellow and yellowish- 

 red sediments, and free uric acid in those of a more purple-red 

 colour. 



All these sediments may contain more or less mucus. 



1. If the sediment consists of urate of ammonia alone, it 

 may be at once recognized by its perfect solution when the 

 fluid is raised to incipient ebullition. To determine this point, 

 the clear fluid is poured from the sediment, some of which is 

 placed in a test tube and heated over the flame of a spirit-lamp : 

 the fluid first becomes transparent on the surface, and gradually 



