HYDROCHLORIC ACID. 



633 



calcium phosphate is found in star-shaped masses of fine prisms (stellar 

 phosphate) (Fig. 58). 



Pathologically, a diminution of the urinary phosphates is seen in nephritis 

 (Purdy), and an increase is said to occur in certain nervous diseases. The 

 phosphates may be greatly increased in diabetes insipidus. 



For the estimation of phosphoric acid the urine is first treated with acetic 

 acid and sodium acetate, and is then titrated with a standard solution of 

 uranium nitrate. Ferrocyanide of potassium or cochineal tincture may be used 

 as an indicator to mark the end point of the titration. 



Hydrochloric acid. There can be little doubt that the greater 

 part of the hydrochloric acid of urine exists as sodium, chloride, and it 



FIG. 58. A. Stellar phosphates ; B. Triple phosphates. 



certainly arises mainly from the common salt present in the food. The 

 tissues and fluids of the body maintain a very constant content of sodium 

 chloride, any excess is at once excreted, and any diminution in the 

 supply immediately reduces the excretion. The amount in the urine 

 depends, therefore, in normal circumstances, almost entirely upon the 

 quantity ingested, and falls to a minimum during starvation, or when 

 a salt-free diet is taken. Pathologically, striking alterations in the 

 chlorides of the urine may be observed. Thus, whenever considerable 

 exudations occur, as in pneumonic processes, or where pleuritic effusion 

 is taking place, the consequent removal of chlorides from the blood may 

 lead almost to a cessation of their excretion ; and conversely, during the 

 reabsorption of such exudations, the urinary chlorides may considerably 

 increase, even when but little salt is being taken by the mouth. Apart 

 from such exudations, fever appears to have a specific effect in pro- 



