84 CLINICAL MICROSCOPY AND DIAGNOSIS. 



(_g) When the relative proportions of the various 

 constituents, which produce acidity, are to be deter- 

 mined the following method gives quite accurate results. 

 10 CO. of the filtered contents are placed in a beaker and 

 decinormal sodic hydrate solution is added, drop by 

 drop, till a drop taken out with a small platinum loop, 

 no longer gives a reaction with the dimethyl-amido-azo- 

 benzol solution. The reading on the burette gives the 

 amount of solution required to neutralize the free HCl 

 (which has the strongest aflSnity for the alkaline solu- 

 tion). 



Now add a loop of the mixture to a drop of Congo 

 red solution. If this still indicates acidity, add more of 

 the soda solution till the Congo red no longer indicates. 

 The reading on the burette gives the amount of alkaline 

 solution required to neutralize the free organic acids 

 present. 



A loop of the contents is next added to a drop of 

 alizarin (indicates alkalinity), and if there is no violet 

 reaction, add the soda solution till this develops. The 

 reading on the burette gives the amount of the soda 

 required to neutralize the acid salts. 



If contents are still acid to phenolphthalein, add 

 more of the soda solution, till the rose-red color com- 

 pletely develops. The reading on the burette gives the 

 amount of solution required to neutralize the combined 

 HCl. 



If there is no free HCl, nor free acid, titration can 

 be commenced at the corresponding portion of the pro- 

 cess just described. 



