15 



4. To a solution 'of quinine sulphate add some tannic acid solu- 



tion. Results. 



5. Add a solution of tannic acid to an albumen solution. Re- 



sults. 



6. Add a little tincture of iron to compound tincture of cin- 



chona. 



Note : — Tannins occurring naturally in plants give a greenish 

 color with iron, while pathological tannins (Nutgalls) give a bluish 

 color. 



Chapter V. 



INCOMPATIBILITY 



Incompatibility means lack of agreement. It may be defined 

 as that condition where two or more agents when brought together 

 result in chemical decomposition, physical disassociation, or thera- 

 peutic opposition. In some cases the change may be desirable, 

 (White Lotion, Black Wash), make little if any difference or may 

 be undesirable. The change may result in precipitating or destroy- 

 ing certain drugs of the mixture, changing color only, forming new 

 compounds without visible change or the ingredients may neutral- 

 ize each other. 



Incompatibility is usually classified as chemical, physical. 

 (Pharmaceutic) and physiological or therapeutic. 



Chemical Incompatibility occurs when a new chemical com- 

 pound results (chemical change). It may, in general, be recog- 

 nized in three ways. 1. Precipitation in wfhieh an insoluble pre- 

 cipitate is formed. 2. Effervescence or explosion-evolution of gas, — 

 and 3. Change in color. In addition a new compound may be 

 formed without any apparent change in the appearance of the 

 liquid with possible disastrous results. 



In order to avoid this form of incompatibility some knowledge 

 of the chemistry of the agents must be understood. A good working 

 basis is that substances are incompatible if used as tests for each 

 other, or if they are antidotes. 



Physical oe Pharmaceutic Incompatibility results in the 

 production of mixtures of unsightly appearance due to physical 

 changes. This is largely a question of solubility and often occur§ 



