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186 A Practical Manual of Pharmaceutical Engineering

(in the form of sand) with two or other materials, e.g., soda ash and lime stone at very high temperatures. Glass containers for pharmaceutical use are intended to come in to direct contact with pharmaceutical preparations. Glass used for pharmaceutical containers is either a borosilicate glass or a soda lime glass. Borosilicate glass contains boric oxide, aluminum oxide, and alkali and/or alkaline earth oxides. It has a high hydraulic resistance. They are classified as Type 1 glass. On the other hand soda lime glass contains alkali metal oxides and considered to have a moderate hydraulic resistance. This will comes under Type 3 glass. If the soda lime glass is treated to improve the hydrolytic resistance they are categorized under Type 2 glasses. The quality of the glass containers is dependent on their resistance to chemical attack.

One of the major problems with the glass container is the alkali extraction when aqueous preparations are stored for a fairly long period. This may cause the increase in the pH of the solution.

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156 A Practical Manual of Pharmaceutical Engineering







To perform the vacuum distillation at varying pressure.

To find out the rate of distillation at varying pressure (vacuum).

To determine the effect of vacuum on the distillation of thermo labile drug (aspirin).


Vacuum distillation assemble (Vacuum pump, claisen flask, Round bottom flask, Measuring cylinder, Separating funnel, Stop cock, Adaptors, Bend tubes Thermometer, Condenser)

Heating mantle


Tripod stand


Burette stands






Vacuum distillation is a distillation process used for materials that have very high boiling-points or are likely to decompose at their boiling-points. Vacuum distillation is a distillation at reduced pressure. Since the boiling point of a compound is lower at a lower external pressure, the compound will not have to be heated to as high a temperature in order for it to boil. The vacuum is provided either by a water aspirator or by a mechanical pump, and the vacuum so formed causes the materials being heated to boil at a temperature lower than they would under normal atmospheric pressure. This enables distillation to take place at lower temperatures. A reliable vacuum

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Crystallization by Cooling


4. Super saturation by adding a substance that reduces the solubility of the substance in the solution.

This experiment is based on crystallization by cooling and is only applicable to the solute whose solubility increases with increase in temperature. Cooling can be done by two methods.

1. Shock cooling

2. Slow cooling

The rate of crystallization during shock cooling is fast and the size of the crystals produced is small. But during crystallization by slow cooling the rate of crystallization is slow, and it will achieve comparatively big crystals. Saturated solutions are prepared by elevating the temperature of the solution. At elevated temperature the solubility exceeds the normal solubility. This solution can be subjected to sudden cooling and slow cooling. During cooling the solubility of the solute decreases as a result the dissolved solute starts to crystallize. The yield is dependent on the time of contact and the temperature. The yield is calculated in terms of percentage. A graph can also be plotted by taking time on X axis and yield in percentage on Y axis.

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Where, d rs ro g

= Diameter of the particle (m)

= Density of the particle(g/cc)

= Density of liquid (g/cc)

= Acceleration due to gravity (m/s2)

From this equation it is possible to determine the terminal velocity of particles of known diameter.

Say suppose particle of size 40 mm, 20 mm etc.

If a suspension taken in a container of known volume, let the height of the suspension in the container is Ho. It is possible to determine the velocity of settling,

V = Ho/t

� (Eq: 18.2)

After rearranging the equation one can find out the settling time for particles of interest. By applying this concept it is easy to separate particles of different size by pre calculating the time for them to settle completely. This experiment allows an easy mode of separation of particle of interest by performing simple decantation procedure.


1. Prepare slurry of calcium carbonate in water (5 g/100 ml).

2. Add this slurry into a beaker (I) and make up to the mark depending upon the capacity of the beaker.

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