118 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



LESSON XI 

 UBINE (continued) 



1. TTrea Nitrate. — Evaporate some urine in a capsule to a quarter of its 

 bulk. Pour the concentrated urine into a watch-glass ; let it cool, and add a 

 few drops of strong, but not fuming, nitric acid. Crystals of urea nitrate 

 separate out. Examine these microscopically. 



2. Urea Oxalate. — Concentrate the urine as in the last exercise, and add 

 oxalic acid ; crystals of urea oxalate separate out. Examine these micro- 

 scopically. 



3. Uric Acid. — Examine microscopically the crystals of uric acid in some 

 urine, to which 5 per cent, of hydrochloric acid has been added twenty-four 

 hours previously. Note that they are deeply tinged with pigment, and to the 

 naked eye look like granules of cayenne pepper. 



When microscopically examined, the crystals are seen to be large bundles, 

 principally in the shape of barrels, with spicules projecting from the ends, 

 and whetstones. If oxalic acid is used instead of hydrochloric acid in this 

 experiment, the crystals are smaller, and more closely resemble those observed 

 in pathological urine in cases of uric acid gravel (see fig. 43). 



Dissolve the crystals in caustic potash and then carefully add excess of 

 hydrochloric acid. Small crystals of uric acid again form. 



Miirexide Test. — Place a little uric acid, or a urate (for instance, serpent's 

 urine), in a capsule ; add a little dilute nitric acid and evaporate to dryness. 

 A yellowish-red residue is left. Add a little ammonia carefully. The residue 

 turns to violet. This is due to the formation of murexide or purpurate of 

 ammonia. On the addition of potash the colour becomes bluer. 



Schiff's Tes^.— Dissolve some uric acid in sodium carbonate solution. Put 

 a drop of this on blotting paper, add a drop of silver nitrate, and warm gently; 

 the black colour of reduced silver is seen on the paper. 



4. Deposit of Urates or Lithates (Lateritious Deposit). — The specimen of 

 urine from the hospital contains excess of urates, which have become deposited 

 on the urine becoming cool. They are tinged with pigment (uroerythrin), 

 and have a pinkish colour, like brickdust ; hence the term ' lateritious.' 

 Examine microscopically. The deposit is usually amorphous — that is, non- 

 crystalline. Sometimes crystals of calcium oxalate (envelope crystals — 

 octahedra) are seen also ; these are coloxirless. 



The deposit of urates dissolves on heating the urine. 



5. Deposit of Phosphates. — Another specimen of pathological urine contains 

 excess of phosphates, which have formed a white deposit on the urine be- 

 coming alkaline. This precipitate does not dissolve on heating ; it may be 

 increased. It is, however, soluble in acetic acid. Examine microscopically 

 for coffin-lid crystals of triple phosphate (ammonio-magnesimn phosphate), 

 for crystals of stellar (calcium) phosphate, and for mucus. Mucus is flocculent 

 to the naked eye, amorphous to the microscope. 



N.B. — On boiling neutral, alkaline, or even faintly acid urine it may be- 

 come turbid from deposition of phosphates. The solubility of this deposit in 



