SEDIMENTS. 135 



(/) Phosphates. 1. Magnesium Phosphate. Rhombic 

 plates, soluble in acetic acid, slightly attacked by ammonium 

 .carbonate. 2. Calcium Phosphate. Soluble in acetic acid. 

 Crystals wedge-shaped, seldom found. 3. Ammonio-magne- 

 sium Phosphate (Triple Phosphate). These separate only 

 when the reaction is weakly acid or amphoteric. 



(g) Potassium Sulphate. Long colorless needles, insoluble 

 in NH 4 OH or acids; seldom found. 



2. AMORPHOUS TYPE. 



(a) Uric Acid Salts (Acid Urates). Brick-red or brown- 

 ish-red in color. Dissolves upon warming and gives the 

 murexide test. Upon the addition of a mineral acid, free 

 uric acid separates out in small crystalline form. 



(6) Calcium Oxalate. Dumb-bell shape. See above for 

 detection. 



(c) Calcium Sulphate. Dumb-bell shape, insoluble in HC1. 



(d) Fat. Strongly refracting round drops, soluble in ether. 



Sediments separating from an alkaline reacting urine: 



1. CRYSTALLINE TYPE. 



(a) Triple Phosphate. Dissolves easily in acetic acid; 

 unchanged by ammonium carbonate (see Magnesium Phos- 

 phate) ; appears under the microscope as large colorless prisms 

 (coffin-cover shape). Upon warming gives off NH 3 . 



(6) Ammonium Urate. Dissolves in HC1 or acetic acid, 

 followed by the separation of free uric acid crystals (rhom- 

 bic form). Forms dark balls with needles radiating from the 

 circumference (chestnut-burs). Gives off NH 3 upon heating 

 on a platinum foil. 



(c) Magnesium Phosphate. See under Acid Urine. 



