16 



when solids or liquids are added to solutions, thereby changing their 

 densities. It occurs when tlhere is a combination 'of such substances 

 as are physically incapable of mixing. The most common physical 

 incompatibilities result from mixing alcoholic solutions of resinoois 

 substances with water, (fluid extracts, tinctures, spirits, etc., ginger, 

 Indian hemp, camphor) , but may not in any way effect the action of 

 the drugs. 



Physiologic or Therapeutic Incompatibility is where two or 

 more drugs are prescribed which are antagonistic or contra-acting 

 to each other in which ease they may almost exactly neutralize each 

 other or one may weaken the action of the other. Arecoline and 

 atropine are good examples, yet no two drugs exactly oppose each 

 other throughout their entire range of action and some latitude is 

 always permitted. 



Incompatibility is a subject very much overdrawn and unneces- 

 sary stress is placed upon it. Although it is possible to find a large 

 number of incompatibilities for any active c'hemical, but few of 

 these are ever likely to be encountered in prescription writing ; and 

 according to Bastedo, of these few, the result not infrequently 

 makes no practical change in the medicinal value or is deliberate- 

 ly desired. According to the same author, the following are those 

 most likely to be encountered in the practical use of drugs : 



I. Incompatibility Depending on Change op Solvent 



A. Precipitate when added to Aqueous Liquids. Substances 

 in alcoholic solution and insoluble in water ; as in spirits, fluid ex- 

 tracts, and tinctures, especially resinous ones, like tincture of can- 

 nabis, benzoin, myrrh. 



B. Precipitation when added to Alcoholic Liquids. Sub- 

 stances in aqueous solution and insoluble in alcohol; as solutions 

 of many salts (sodium sulphate, ammonium chloride) and muci- 

 lage of acacia. Mere insolubility as of oils or bismuth subnitrate 

 in water, makes these really incompatible with the solvent. 



II. Chemical Incompatibilities 



Rule 1. Acids and salts of acid reaction are incompatible 



with alkalies and salts of alkaline reaction and the halogen salts. 



Rule 2, Highly oxidized substances, like chromium triox- 



