When two or more than two substances are combined together, a physical change takes
place and an unacceptable product is formed. Physical incompatibility is usually due to
immiscibility, insolubility, precipitate formation or Liquefaction of solid material.
(Consider any one e.g)
Immiscibility:
Rx
Castor oil .......15 ml
Water ............. 60 ml
Make an emulsion
Oil and water are immiscible with each other. they can be made miscible
with water by emulsification.
In this prescription castor oil is immiscible with water.
To overcome this incompatibility an emulsifying agent is added.
Insolubility: Liquid preparation containing indiffusible solids such as chalk, aromatic chalk
powder, aspirin etc, a suspending agent may be incorporated so as to increase the thickness
0f preparation which helps in uniform distribution of solid and solid are suspended for long
time after shaking.
Rx
Phenacetin …….3 gm
Caffeine …………1 gm
Orange syrup ….12 ml
Water upto ….. 90 ml
Make a mixture
Precipitation: A drug solution can be precipitated if solvent is added in which they are
insoluble, or when tincture are present and it is diluted with aqueous solution resin tend to
get precipitate out, which may get stick to the side of the bottle, therefore suspending agent
like tragacanth powder or tragacanth mucilage has to be added.
Rx
Tincture benzoin ………5 ml
Glycerine ………………..15 ml
Rose water ……q.s …100ml
Make a mixture
Liquefaction: When certain low melting point solids are mixed together they form a new
chemical compound which has melting point lower than room temperature, therefore they
become liquid at room temperature.
Rx
Menthol --------------------------- 5g.
Camphor -------------------------- 5g.
Ammonium chloride ------------ 30g.
Light magnesium carbonate ---- 60g.
Send five powders
The combination forms eutectic mixture.