It is presumed that a student is familiar with the theoretical aspects of solution. When a soluble solid is incorporated in a liquid, its physical form is changed.
Essentially it is a phenomenon of mass transfer. After due scrutiny of the prescription, one should be able to envisage and assess whether the prescription would yield a clear product.
Lack of comprehension may result into filtering out and rejecting the therapeutically active precipitate in an over enthusiastic attempt to supply a clear product. Such instances are not rare and it is vital that a pharmacist fully understands the likely reactions that may occur and act suitably.
Once it is established that a solution will result he may take steps to affect it rapidly. Drugs in fine state of subdivision have a greater specific surface and dissolve faster than larger particles or crystals.
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Secondly, stirring the particles in the vehicle expedites dissolution as highly concentrated solution around the particle is replaced by dilute solution till the equilibrium is established. Raising the temperature usually accelerates the rate of solution.
However, heating may not be advisable to if the drug is thermo-labile. Rise in temperature increases the diffusion coefficient and reduces the viscosity, two important factors that favor solution.
As a rule, the pharmacist should not rely on his memory regarding the solubility of ingredients. It is advisable that he makes use of tables and texts for ascertaining solubility of the substances in given vehicle under the overall conditions of the prescription. When two substances are present to the optimum amount of their solubility, it is likely that the resultant product may not be clear.
Further, the pharmacist should thoroughly examine the possibility of a chemical reaction resulting into precipitate formation. The drug is first powdered and the requisite quantity weighed.
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Stirring or shaking with a liquid may be done preferably in a conical flask large enough to prevent spilling during shaking. Another method for affecting solution of relatively less solute substances is to transfer the solid and a portion of the vehicle in a mortar and mixing with the help of pestle.
Wherever volatile substances are prescribed, heating should be avoided as a precautionary measure and shaking done in a closed container with a suitable closure to prevent loss of volatile medicament. Whenever heating has been employed, the solution should be first cooled to room temperature, if need be, under running tap water.
Filtration, dilution, making up the volume and transference to the container should be done thereafter.