114 



PRACTICAL PHYSIOLOGY. 



[xvn. 



8. In some pathological urines the phosphates are deposited on 

 boiling. 



(a.) Boil such a urine = a precipitate. It may he phosphates or 

 albumin. An albuminous precipitate falls before the boiling-point 

 is reached, and phosphates when the fluid is boiled. Add a drop 

 or two of nitric or acetic acid. If it is phosphates, the precipitate 

 is dissolved ; if albumin, it is unchanged. 



9. Microscopic Examination. As the alkaline phosphates are 

 all freely soluble in water, they do not occur as a urinary deposit. 

 The earthy phosphates, however, may be deposited. 



(a.) Examine a preparation or a deposit of calcic phosphate, 

 which may exist either in the amorphous form or the crystalline 

 condition, when it is known as "stellar phosphate" (fig. 55). 



(b.) Prepare " stellar phosphate " crystals by adding some 

 calcium chloride to normal urine, and then nearly neutralising. 



FIG. 55. Stellar Phosphate. FlG. 56. Various Forms of Triple Phosphate. 



On standing, crystals exactly like the rare clinical form of stellar 

 phosphate are obtained. 



(c.) Triple Phosphate ' or ammonio - magnesic phosphate 

 Mg(NH 4 )P0 4 + 6H. 2 never occurs in normal urine, and when 

 it does occur, indicates the decomposition of urea to give the 

 ammonia necessary to combine with magnesium phosphate to form 

 this compound. It forms large, clear "knife-rest" crystals (fig. 56). 



('?.) If ammonia be added to urine, the ammonio -magnesic 

 phosphate is thrown down in a feathery form, which is very rarely 

 met with in the investigation of human urine clinically (fig. 57). 



10. General Rules for all Volumetric Processes. 



(a.) The burette must be carefully washed out with the titrating 

 solution, and must be fixed vertically in a suitable holder. 



