210 URINARY SEDIMENTS. 



angles may not be so truncated and the long axis of the 

 crystal may be so much shortened that it assumes the form 

 of an octahedron, like the calcium oxalate. Unlike the 

 latter, it is soluble in acetic acid. Calcium phosphate in 

 the urine is usually amorphous, and always colorless. It 

 is formed when the urine becomes alkaline in the absence 

 of ammonia. To the unaided eye it resembles pus, but 

 differs from it in its solubility in acids. In acid urine the 

 acid phosphate, CaHP0 4 , may crystallize in long prisms, 

 usually in clusters. Tribasic calcium phosphate, Ca 3 - 

 (P0 4 ) 2 , is colorless and amorphous. (Plate II, 7.) 



The presence of phosphates may be due1;o an excessive 

 formation in the body, and they are then usually accom- 

 panied by systemic disturbances. Alkalinity of the urine 

 causes their appearance when there is no excess. This may 

 be from the food or medicine, from an increase in the alka- 

 linity of the blood, or from fermentation. Excessive men- 

 tal work is often accompanied by phosphatic sediments. 

 Their long-continued presence may excite fear of the 

 formation of calculi. Their temporary appearance is a 

 matter of no grave significance. In urine which has stood 

 for a time after its passage they are the most common of 

 the sediments. 



421. Drop ammonia into normal urine until it is 

 slightly turbid, and after it has settled examine the sedi- 

 ment with the microscope. It is a mixture of the amor- 

 phous calcium phosphate and crystalline triple phosphate. 

 To obtain a larger amount of the latter add to the urine 

 a little magnesium sulphate before it is made alkaline. 



422. Precipitate sodium phosphate with magnesium 

 sulphate after making alkaline by ammonia. Notice the 

 difference in the shape of these stellate crystals under the 

 microscope and those usually formed in the urine. Try 

 the solubility of both forms in acetic acid. 



