NON-ORGANIZED SEDIMENTS. 783 



with a drop of hydrochloric acid small crystals of uric acid are obtained 

 which can be easily seen under the microscope. 



Acid Urates. These occur only in the sediment of acid or neutral 

 urines. They are amorphous ; clay-yellow, brick-red, rose-colored, or 

 brownish-red. They differ from other sediments- in that they dissolve 

 on warming the urine. They give the murexid test, and small micro- 

 scopic crystals of uric acid separate on the addition of hydrochloric 

 acid. Crystalline alkali urates occur very rarely in the urine, and as a 

 rule only in such as have become neutral but not alkaline by alkaline 

 fermentation. The crystals are somewhat similar to those of neutral 

 calcium phosphate; they are not dissolved by acetic acid, however, 

 but give a cloudiness therewith due to small crystals of uric acid. 



Ammonium urate may indeed occur as a sediment in a neutral urine 

 which at first was strongly acid and has become neutralized by the alkaline 

 fermentation, but it is only characteristic of ammoniacal urines. This 

 sediment consists of yellow or brownish rounded spheres which are often 

 covered with thorny-shaped prisms and, because of this, are rather 

 large and resemble the thornapple. It reacts to the murexid test. It 

 is dissolved by alkalies with the development of ammonia, and crystals 

 of uric acid separate on the addition of hydrochloric acid to this 

 solution. 



Calcium oxalati occurs in the sediment generally as small, shining, 

 strongly refractive quadratic octahedra, which on microscopical examina- 

 tion remind one of a letter-envelope. The crystals can only be mistaken 

 for small, not fully developed crystals of ammonium-magnesium phos- 

 phate. They differ from these by their insolubility in acetic acid. The 

 oxalate may also occur as flat, oval, or nearly circular disks "with central- 

 cavities which from the side appear like an hour-glass. Calcium oxalate 

 may occur as a sediment in an acid as well as in a neutral or alkaline 

 urine. The quantity of calcium oxalate separated from the urine as 

 sediment depends not only upon the amount of this salt present, but 

 also upon the acidity of the urine. The solvent for the oxalate in the 

 urine seems to be the diacid alkali phosphate, and the greater the quan- 

 tity of this salt in the urine the greater the quantity of oxalate in solu- 

 tion. When, as previously mentioned (page 782), the simple-acid phos- 

 phate is formed from the diacid phosphate, on allowing the urine to 

 stand, a corresponding part of the oxalate may be separated as sediment. 



Calcium carbonate occurs in considerable quantities as sediment in 

 the urine of herbivora. It occurs in but small quantities as a sediment 

 in human urine, and in fact only in alkaline urines. It either has the 

 same appearance as amorphous calcium oxalate or it occurs as some- 

 what larger spheres with concentric bands. It dissolves in acetic acid 

 with the generation of gas, which differentiates it from calcium oxalate. 



