Physiochemical processes

Evaporation ExsiccationIgnition CrystallizationDistillation SublimationFusion CalcinationAdsorption DecantationVaporization PrecipitationCentrifugation DesiccationLevigation TriturationEfflorescence DeliquescenceLyophylization Elutriation

Precipitation

Precipitation or the process of separating the solid particles from the solution by physical and or chemical changes" The separated solid particles are called PPT, while the remaining clear liquid above the PPT are called as ''supernatant''Applicants of Precipitation Following are the some important cases or applications of PPT process:1-The precipitation method is used to produce very fine solid particles, about 0-1m.2-It is also used to purify the solids. (Drugs)3-It is also used in the purification for of organic and inorganic compounds.

Methods of Precipitations

There are three different method of Precipitation as follows:

1- Organic solvent method2- pH change method3- Double decomposition method 1- Organic solvent method:- In this method the water insoluble substances or (drugs) are dissolved in water miscible organic solvents. Now the dissolved drug can be easily precipitated by adding water (distilled water) into the mixture.The general organic solvents are Ethanol, Methanol, Glycol, Propylene glycol, polyethyleneglycol.When (prednisolone) suspension is dissolved in methanol, it is very easily precipitated by adding distilled water.Only physical changes occur in this process.

Methods of Precipitations2- pH Change MethodThis method is applicable only to those substances (drugs) in which solubility are dependent upon pH. (Esterdiol suspension) is prepared by changing the pH of the aqueous solution. Esterdiol drug is readily soluble in alkaline media (NaOH and KOH) solution.However this drug is insoluble in acidic media. So when this drug is added to an acidic media ( HCI, acetic acid or citric acid ) with proper agitation Esterdiol is easily precipitated out in a form of fine particles. Insulin solution can also be prepared by pH change method. The PH change method is again a physical change. (Not a chemical change)

Methods of Precipitations3- Double Decomposition Method:Precipitations are formed in this method only by simple chemistry.MgCO3 and CaCO3 are the common substances prepared by this method

CaCl2 + Na2CO3 -----------> CaCO3 + 2NaCl

MgCl2 + Na2CO3 -----------> MgCO3 + 2NaCl

Hot concentration solution produce coarse PPT, from which impurities can be removed by washing, but PPT formed by dilute solution are much finer and it is much difficult to remove impurities from them. In many case the order of mixing solutions can also effect the PPT formation, e.g.

Methods of PrecipitationsSimilarly (white lotion) is formed by precipitation i.e. by mixing aqueous solution of ZnSO4 and Sulphurated Pottaish to form insoluble PPT, which finally divided into Zinc sulphide plus free sulphur and various polysulphides e.g, Zn SO4 + sulphurated potash ---------> ZnS + S +Many other organic and inorganic compounds are formed by precipitation methods e.g. Mg sterate is formed by treating diluted solution of sodium stearate and MgSO4 . PPT of Mg sterate are formed and are formed and are washed with water.

EVAPORATION

Theoretically evaporation means the free escape of vapours from the surface of a liquid below its boiling point. It is a slow process that can take place even at room temperature. Evaporation will be maximum at the boiling point of the substance. Evaporation differ from boiling in that, evaporation takes place at all temperatures where as boiling takes place only at one temperature at a given pressure.Evaporation occurs only at the surface of a liquid, but in boiling evaporation takes place from whole of the liquid. Boiling occurs when the vapours pressure of the liquid becomes equal to the atmospheric pressure.Evaporation differ from distillation, that in evaporation the solvent which is generally water is not condensed and collected where as in distillation the solvent vapours are condensed and are collected in a receiver.

FACTORS AFFECTING EVAPORATIONTemperatureSurface areaAgitationAtmospheric aqueous pressureAtmospheric pressure on the liquid under evaporationType of product requiredEconomic factors

Temperature

The rate of evaporation is directly proportional to the temperature.Higher the temperature higher will be evaporation but evaporation is at its maximum at the boiling point of the liquid. Thermostable preparations can be evaporated at higher temperature but the thermolabile preparations will have to be evaporated at low temperature.Many substances like glycosides, alkaloids, hormones, enzymes and antibiotics may get decomposed even at temperature below 100C and hence they should be evaporated at low and careful temperature. Extremely heat sensitive substances are evaporated under reduced pressure.

Temperature

Time required for evaporation is very critical. Exposure to a higher temperature for a shorter period of time may be less destructive than a lower temperature with exposure for a longer period of time. Therefore as for as possible evaporation should be carried out for short time at low temperature.Therefore evaporation in some cases may be carried out at a low controlled temperature till a concentrated product is obtained.

Surface area:The rate of evaporation is directly proportional to the surface area of the vessel exposed to evaporation. Greater the surface exposed to evaporation higher will be the rate of evaporation.

AgitationDuring evaporation the upper layers of the liquid to be evaporated has a tendency to form a scum or layer which lowers the rate of evaporation. Therefore it becomes necessary to agitate or stirrer the solution under evaporation. This will also prevent the decomposition of the preparation at the bottom due to excessive heat and will also prevent the settling of the solids at the bottom of the container.

Atmospheric aqueous vapour pressure If the atmospheric aqueous vapour pressure or moisture contents in the air are high, the rate of evaporation will be slow but if it is less then evaporation will be fast. Therefore rate of evaporation can be increased by free circulation of warm air over the evaporating pan.

Atmospheric pressure on the liquid under evaporation The rate of evaporation is inversely proportional to the atmospheric pressure on the surface of the liquid. If the atmospheric pressure on the liquid is reduced to half then the rate of evaporation will be doubled. Due to this reason in many cases the evaporation is done under reduced pressure i.e. by producing vacuum over the surface of the liquid.

Type of product required The selection of the method and apparatus to be used for evaporation depends upon the type of product required. Evaporating pans or stills may be used to produce liquid or dry products.

Economic factors While selecting the method and apparatus employed for evaporation, due consideration must be given to economy of labor, fuel, floor area and materials. The recovery of solvents and the utilization of "waste" heat are also important factors, which contribute significantly in the reduction of overall costs.

A) Small scale methods

Small quantities of liquids can be evaporated in a glass dish. Generally direct heating by burner or electric hot plate is used for evaporation. But these should not be employed because direct heating leads to the decomposition of the substances towards the end of evaporation. So for this purpose different types of bathes are used as a source indirect heating. A water bath is most suitable when the liquids are to be heated up to100C.Glycerine bath is used to attain a temperature up to 150C. Sand bath or oil bath containing liquid paraffin or soft paraffin may be used when higher temperature up to 300C is required.To prevent decomposition, whole of the liquid should not be evaporated to dryness. The last traces of the solvent from the concentrated liquid may be removed under controlled temperature.

B) Large Scale Methods

Evaporating pansEvaporating stills1) Evaporating pans. On large scale, liquid extracts containing water as a menstrum are evaporated in open pans called evaporating pans. These consist of hemispherical or shallow pans made of copper, stainless steel, aluminum, iron or other metals and surrounded by a steam jacket. Pans made from stainless steel and jacket from iron is most suitable. The hemispherical shape is most suitable because it provides the best surface to volume ratio for heating. The pans may be fixed or made to tilt to remove the product.

Evaporating pans

Evaporating pansAdvantagesThey are simple, easy and cheap to construct.Easy to use and clean.Stirring of the evaporating liquid can be done easily

DisadvantagesThe whole of the liquid is heated all the time, which may lead to thedecomposition of the component.Solids may be deposited at the bottom, which makes the stirring necessary.These pans can only be used for evaporating aqueous and thermostable liquidextracts.The room in which evaporating pans are used for evaporating the liquids must be fitted with efficient exhaust fans otherwise the room will be filled with dense fog of condensed vapours.

2) Evaporating stills Evaporating stills are quite similar to evaporating pans. The vessel is made of cooper stainless steel, with a cover, which is fitted with a water condenser so that the solvent is condensed and collected in a receiver. At the lower point of the pan, a tube fitted with a tape is connected for the removal of the product from the pan. A steam jacket surrounds the pan. For cleaning the pan or easy removal of the product the cover of the vessel may be fitted with quick release system of clamps.

Evaporating stills

Evaporating stillsAdvantages They are very simple to construct and easy to clean.A vacuum pump can be fitted to the apparatus by which evaporation under reduced pressure can be doneSince the cover can be removed easily therefore the still may be conveniently used for evaporating extracts to dryness.Disadvantages The whole of the liquid is to be heated all the time, which may lead to deterioration of the product. This method is used only for the small batches of liquids which are to be evaporated.

Evaporating stillsApplications of evaporationThis process is used in the preparation of liquid extracts, dry extracts and in the concentration of blood serum.It s also used in the manufacture of drugs

Exsiccation

Exsiccation is the process of removing the water of crystallization from the hydrated crystalline substances by heating and making them less hydrous or anhydrous.The examples of exsiccated substances include exsiccated ferrous sulphate, exsiccated magnesium sulphate, exsiccated sodium sulphate, exsiccated sodium carbonate, exsiccated alum and anhydrous sodium arsenate.In the laboratory, exsiccation may be carried out by taking a weighed amount of the substance in a tared dish which is heated on water bath, sand bath or in an oven, with continuous stirring until a constant weight is obtained or until the calculated loss in weight has taken place.

Exsiccation

The temperature required to remove 'water of crystallization is very important. For example, copper sulphate, CuSO4 . 5H20, when heated at about 30C loses two molecules of water of crystallization, at 100C it loses two more water molecules and the last water molecule is removed when it is heated at 200C, thus forming CuSO4. 3H2O, CuSO4.H20 and CuSO4 respectively. Similarly ferrous sulphate FeSO4.7H2O when heated on water bath loses six molecules of water of crystallization 'but when further heated to remove last water molecule, decomposition takes place. Hence ferrous sulphate with one molecule of water of crystallization FeSO4.H2O is called exsiccated ferrous sulphate.Since the exsiccated salts are very hygroscopic, they must be stored in well closed containers.

ExsiccationApplications1. Exsiccation is done to get an anhydrous product required in the formulation of certain medicaments.2. It is also carried out to reduce the bulk and weight of certain drugs so that they can be easily administered.3. Generally on exsiccation a fine powder of the substance is obtained.

Desiccation

Desiccation is the process of removing adhered moisture from liquid or solid substances. The term "desiccated" should be used for those substances from which water has been completely removed.

Desiccation

Desiccation

On laboratory scale desiccation can be carried out in a desiccator, which consists of a tightly closed glass vessel containing a drying agent at its bottom, which absorbs moisture from the substance being desiccated. The commonly used drying agents include concentrated sulphuric acid, phosphorous pentoxide, exsiccated calcium chloride and silica gel. The drug to be dried is taken in a dish, which is placed inside the desiccator above the surface of drying agent. For continuous operation the desiccator may sometimes be connected to a vacuum pump.

Desiccation

The substances which are very sensitive to moisture are formulated as tablets or capsules which are further protected by enclosing them in sealed vials, on the bottom of which a small cloth bag containing silica gel is placed which acts as a desiccant.

Desiccation

ApplicationsDesiccation helps in preserving the vegetable and animal drugs which get destroyed in the presence of moisture.2. Comminution of drugs is difficult if they are wet but if they are dry, can be easily powdered.3. Desiccation reduces the bulk and weight of the substances due to loss of adhering moisture in them therefore they become easy to handle.4. Stability of certain drugs is also increased.

EFFLORESCENCE

The large no of chemical compound exists in hydrated or anhydrous form. In hydrated form the water molecule attached to the compound are called the water of crystallization. The surrounding atmosphere also has vapours and definite vapour pressure, due to water in atmosphere. If the vapour pressure of the hydrated substance is greater than the surrounding atmosphere, than the hydrated substance loses water molecule to become less hydrous and to make an equilibrium between the hydrated substance and the atmosphere.

EFFLORESCENCE

This phenomenon is called efflorescence. In simple words efflorescence is the loss of water of crystallization from the hydrated substances into the atmosphere so that an equilibrium is formed b/w the hydrated substance and the surrounding atmosphere.

Examples:Examples of Efflorescent substances are;1. Borax Na2B4O7.H2O (Hydrated substance) 2. Na2SO4.10H2O3. Na2CO3.10H2Oe.g. Z4SO4.7H2O and MgSO4.7H2ONa2CO3.10H2O loses 9 water molecules first and then becomes completely anhydrous as follows;

SpontaneousNa2CO3.10H2O ----------------------> Na2O3 .H2O Efflorescence ||\ || || Na2CO3 (Anhydrous0

Since the vapor pressure of the hydrated substance is greater then the atmospheric vapor pressure, so there is a spontaneous loss of water of crystallization till the equilibrium is obtained. After the equilibrium formation number more loss of water molecules occur.

Prevention of Efflorescence Efflorescence or loss of water of crystallization can be prevented by the following ways:By closing the container immediately after use.By filling the container completely so that no space for air storage is available above the liquid in the container. By placing a dehydrating agent (silica gel) to absorb water.

DeliquescenceDeliquescence is a reverse of efflorescence.If a hydrated substance has a lower vapour pressure, than the surrounding atmosphere than the water molecule transfer from the atmosphere to the less hydrated substance to make them more hydrated and to produce a equilbrium.This phenomenon is called deliquescence. e.g.: NaOH

Prevention of DeliquescenceBy closing the container immediately after using it.By filling the container completely so that no space for air storage is available above the liquid in the container.By placing the dehydrating agent e.g: (Silica gel)to absorb water.

Distillation

Definition: Distillation is the process of separating volatile substances from non-volatile substances. In other words Distillation is the process of separating the constituents of a liquid by vaporizing the liquid and then passing the vapors through a cold surface and converting the vapors again into liquids. Hence distillation involves the change of state from liquid into vapor (gas) and again into liquid state. (Gas)Liquid-------------- > Vapors ------------- > Liquid

Types of Distillation:1- Simple Distillation2- Steam Distillation3- Fractional Distillation4- Distillation under reduced Pressure

1-Simple Distillation

Definition: Simple distillation is the process used for the precipitation of many organic compounds. In this process simple apparatus is used.

Process:A liquid is converted into vapors by heating up to boiling round bottom flask or still. The vapors are then passed through apparatus called condenser, which cool the vapors and reconverted the vapors into liquid (distillate). This distillate is collected in suitable vessels called as receiver. The apparatus used for distillation consists of the following components.

Apparatus

1- Still: - the container in which the volatile substances and heated is called as still. In still actually the liquid is changed into vapors. (gas)

2- Condensers: - Condenser is the apparatus in which the prepared vapors are converted into liquid again by cooling.

3- Receiver: - The distillate is called the receiver.

Application of Simple Distillation

The process of distillation is used in the purification of many organic compounds e.g. ethers, amide, Nitrile etc.This process is also used to separate the volatile substance from non-volatile solvent e.g. preparation of distilled H2O for injection.It is used in preparation of drug extract, volatile liquid such as alcohols or others are recovered by distillation process.

Fractional Distillation

Definition: Fractional distillation is the process used to separate more volatile liquids having different vapor pressures and different boiling point Alcohol is more volatile than the water. Hence alcohol will separate earlier then water. It is easy to separate non-volatile liquids from volatile liquids by simple distillation method but it is very difficult to separate two volatile liquids completely from one another by simple distillation. Such miscible liquids are separated by using fractional columns.

Fractional ColumnsFractional columns are of different types having different lengths. The long columns are necessary when there is a small difference between the boiling points of the two miscible volatile liquids. However the short columns are used, where there is a great difference between the boiling points of two miscible liquids. The vapors must pass these fractionating columns before reaching the condenser. Partial condensation of these vapors occurs in these fractionating columns also.

Fractional ColumnsThe fractionating columns are inserted between the still and condenser. Fractionating column is a device which increase the process of fractional distillation by condensing most of the vapor of less volatile component of the mixture and return it to the still, where as vapor of more volatile component of the liquid are allowed to pass trough the condenser. When the vapors of more volatile liquids pass through these columns, while the liquid having high boiling point will be condensed back into the liquid state and will arise latter to the top of the fractionating columns.So vaporization and condensation take place through out the length of fractionating columns.

Process: In the fractional distillation proper length are fitted between the stilled condensers. The liquid mixture is added of the still or boiler and is heated . The upper ends of the columns are fitted with thermometer which indicates the temperature at which more volatile substances are distillated. The other side of these columns is connected with a condenser which condenses the vapors and the liquid distillated is collected in the receiver.

Application of Fractional Distillation

1- Fractional distillation is used for the preparation of alcohol, which is one of the important pharmaceutical substances.95% rectified spirit is obtain by the fermentation of starch by the action of yeast. Yeast is the common source of ethanol containing Ethanol containing 8-10% alcohol. It is purified by fractional distillation to form 95% ethanol or rectified spirit. The boiling point of Ethanol is 78.5C.

Steam Distillation

The distillation of two immiscible liquids in which one of the immiscible liquid is water, the process is called as Steam Distillation." The immiscible liquid and water boil at high temperature. However, when steam is passed through the mixture of these liquids, then they boil at a much lower temperature. (Even less then the boiling point of water). Many organic compounds which are insoluble in water can be separated and purified by this process, but at much lower temperature then their original boiling point. For example, Turpentine oil has boiling point 160C, but when it is mixed with water, it can be distilled at a temperature of 75C, which is below the boiling point of water. Similarly Bromo-Benzene has normal boiling point 156.2C. When it is mixed with H2O, it is distillated at a temperature of 61C which is below the normal boiling point of water.

ProcessThe apparatus used for steam distillation consists of a steam container, flask or still, receiver and condenser. The steam container has two holes. Safety tube is fitted in one hole and reaches the bottom. Another tube is fitted in the other hole which carries the steam into the still or flask. The safety tube must reach the bottom of the container. If the pressure rises of the steam becomes to much to be controlled, then extra steam comes out through this tube.

The mixture of immiscible liquids is placed in the still or flask.

The flask and the steam container are heated simultaneously, so that a rapid current of steam passes through the boiling mixture. The vapors are allowed to pass through condenser.

Distillation is continued till the whole mixture is collected in the receiver. The distillate in the receiver has two layers, one aqueous and other non-aqueous, which are then separated from each other.

THE EQUIPMENT

Applications of Steam DistillationSome applications of steam distillation are as follows:1- Many organic compounds can be purified without decomposition by steam distillation.2- Volatile oils can be extracted from crude oils by steam distillation. 3- Aromatic water is prepared by this process."Aromatic Water: Aromatic water is defined as the saturated solution of volatile substances." For example, Anise water, Chloroform Water, Rose water.

Distillation under reduced pressureDefinition: The process of separating two miscible liquids having different boiling point and different vapor pressure, by reducing the internal pressure of the system" For example, At normal atmospheric pressure (760mmHg), the boiling point of the water is 100C. If the pressure is reduced to (4.5mmHg), then the water boils at 0 which is the normal freezing point of water.

Laboratory level vacuum Distillation,

Classian Flask apparatus is used in vacuum distillation process. The classian flask has two open mouths. A capillary tube is fitted in one open mouth to reduce the vapor pressure. A thermometer is fitted in the other open mouth to note the temperature. Sometimes one extra capillary tube is fitted in this open mouth for reducing the internal pressure rapidly.

The vapor form Classian Flask then pass through the condenser fitted with the flask. The vapors are then re-converted into distillate. The distillate is then stored in the receiver.

A vacuum pump is fitted with receiver to reduce the internal pressure. When the internal pressure is decreased through the pump, then the liquid boils at low temperature.

Large Scale industry vacuumDistillation

The apparatus used for vacuum distillation on industrial scale consists of large, still, containing the mixture or liquids to be distillated. A thermometer is fitted with still. The still is connected with spiral condenser. The condenser is fitted with vacuum pump in order to reduce the internal pressure. The distilled is stored in receiver finally. When heat is provided to the still containing liquids, the liquids start vaporizing and when these vapors pass through the condenser, they are converted back into liquid or distillate which is stored in the receiver. The pressure is continuously reduced through the vacuum pump.

Application of vacuum distillation Following are the some important uses of vacuum distillation:1- Various impure liquids are purified by this process without decomposition.2- This vacuum distillation is used for the separation of (Thermolabile, heat sensitive) substances.3- Extracts or crude drugs are prepared by this process.

Destructive Distillation

The process of break down of or decomposition of natural substances is called as destructive distillation. For example, destructive distillation of coal, wood etc.

SUBLIMATION

Sublimation is the process in which transforming the solid to vapors without intermediate passage through the liquid state.

Triple point.Triple point is the point having a definite temperature and pressure at which the solid, liquid and vapor phases of a chemical substance co-existTriple point is a point in a graph between temperature and pressure at which three phases like solid, liquid and vapours may co exist.

Method of sublimationThe pressure below the triple point is called as Sublimation pressure.In the diagram the line (AO) is known as sublimation pressure. At this (O) point solid and liquid are at equilibrium. If the sublimation pressure is below this triple point the solid will directly converted into vapor phase and the vapor phase is directly change into solid. Two factors in the diagram indicate that:When the vapor pressure of the substance is less then that of sublimation pressure, it will directly change into solid or vapor phase without changing into liquid phase.

Method of sublimationWhen the vapor pressure of the substance is high then that of the sublimation pressure, then it will first convert into liquid phase and then into solid state on further cooling.The common sublimed substances are as follows:Iodine NaphthalineCamphorPara-dichloride benzeneThus the vapor pressure of Iodine, camphor, Naphthaline and p-dichloride benzene are less triple point.

Method of sublimationIn laboratory it consists of a china dish, a perforated filter paper, funnel, and a cotton plug.The material to be sublimed is placed in the china dish; the china dish is covered with a perforated filter paper. A glass funnel is placed in the inverted position over the filter paper; the open end of the funnel is plugged with cotton to prevent the escape of sublimed product.The china dish is heated and vapors pass through the perforations of the filter paper, and are collected on the inner surface of the glass funnel which is kept cool from out side by wrapping a wet filter paper or cotton wool. The vapors on cooling are condensed into solid which is collected.

APPLICATIONS This process is used in the purification of many pharmaceutical substances such as iodine, camphor, naphthalene, benzoic acid, mercuric chloride, ammonium chloride.This process is also employed to purify volatile solids contaminated with non volatile impurities.

Lyophilization /freeze drying

Freeze drying is the process of drying in which water is sublimed from the product after it is frozen.

Process: The freeze drying process is simple but more complicated as follows: During the process the temperature must be less below the triple point in range of -10C to -30C. Similarly the process must also be kept below the triple point. (4.6mmHg)

Lyophilization /freeze dryingThe substance or solution is kept in a drying chamber. The NH3 and Freon gases are used as refrigerants in the chambers from the compressor through a pipe. The chamber and condenser are then evacuated by the vacuum pump. The heat is then introduced by electric resistant coil or by circulating hot water. The process continues until the product is dried. The provision of heat is controlled to avoid dissociation of the substance. The vapor produced in the chamber must be removed continuously to avoid pressure rise, which would stop sublimation. So vapors are continuously removed by pumping. This process is very prolonged and may take several hours for completion.

Lyophilization or freeze dryingApplication:Liophilization is applied to prepare many biological substances e.g. blood plasma, vitamins, hormones, enzymes, vaccines, antibodies.Freeze drying process is used to dry freeze and to preserve the biological substances and for the preservation of different types of food product.

Advantages:

Following are the some advantages of this phenomenon, Freeze drying take place at very low temperature, so the decomposition of the substance is minimized. The biological and pharmaceutical substances which are unstable in aqueous solution are stored in dry state. Freeze drying products are light and porous and are usually readily soluble. The product which are degraded or dissociated by oxidation can be freeze dried, without dissociation.

DisadvantagesFollowing are the three main disadvantages of this phenomenon:1. The product becomes hydroscopic and dried and can be easily dissolved. (porous product) 2. The process is very slow and much more time is wasted. 3. This process is very expensive and therefore is restricted to certain types of valuable products that cannot be dried by any other process.

Spray Drying

Spray drying is one of the methods of desiccation by which solutions or slurries are dried. The apparatus used for this purpose is known as spray drier. These driers consist of a hot air chamber into which liquid to be dried is fed from the top and hot air is supplied from the base. The spraying of the liquid is done either by pressure jets .By the high current of hot air the liquid is sprayed in the form of a mist, the droplets of which are readily evaporated and the dried particles fall to the bottom of the chamber from where they are collected. The exhausted air leaves the chamber through the air outlet.Different types of spray driers are available with various modifications. In some forms of spray driers the liquid to be dried and hot air enters from the top of the chamber and in others from the bottom. Still in other types liquid is fed from the top and hot air from the bottom.

Applications

1. These driers are very useful because the drying is very rapid as large surface of liquid is exposed to hot air and temperature required for drying is also low. Therefore heat sensitive products can be dried conveniently.2. Spray drying is used for drying blood plasma, milk and enzyme preparations such as pancreatin and pepsin.3. Spray driers can be designed for drying under sterile conditions.4. Solid and liquid particles can be encapsulated by employing pray drying.

Fusion/meltingFusion is the process by which the solids gets converted into liquids without adding any solvent. It may also be defined as the process of heating the solids until they melt.Fusion is done to purify certain solid and semisolid substances e.g. bees wax, hard paraffin, soft paraffin and wool fat are heated to melt and filtered while hot, to remove the dissolved impurities. On cooling, a product free from dissolved impurities is obtained. This method is also applied for the preparation of ointments when they also contain solids and semisolids in the formulation. All the substances are melted and then cooled slowly with continuous stirring until a uniform product is obtained. To avoid overheating substances with higher melting points are melted first to' which substances with lower melting points are added.

Calcination /Roasting.

Calcination is the process in which the inorganic substances are strongly heated so as to remove their volatile contents and a fixed residue is obtained. On laboratory scale calcination is done in silica or platinum crucibles where as in industries metallic vessels are used.

Explanation: In process of calcinations the product are obtained by heating the substances especially ores of minerals. The principle ores which can be calcinated are oxides, carbonates, silicates, sulphites and halides of metals. The gases formed during roasting of ores especially sulphides, arsenic fumes etc.The ore is added into one end which is then shifted towards the fire box and removed after 3 hours, e.g. MgCO3 is roasted or calcinations give MgO.

MgCO3 --------------------------- > MgO + CO2 Heat Fe2SO4 -------------------------- > Fe2O3 + SO2 HeatCuSO4 --------------------------- > CuO + SO2Application:This process is used for manufacturing of inorganic compounds from natural sources e.g. formation of MgO which are used as ant acid.

Ignition

Definition: The process in which synthetic compound or drug is burnt at high temperature on electric furnace to remove the organic substance (carbon) and left behind the inorganic substance (as residue as ash) is called Ignition. Explanation: Known quantity of substance is ignited in silica crucible electric furnace. The substance is ignited at specific temperature for definite time is electric furnace

Ignition

After ignition the crucible is placed in dissector containing a suitable desiccant (moisture absorber) and allowed to cool for 25-30 minutes. The crucible is weighed. The crucible and the contents are again ignited at the same temperature for 30 minutes. The ignition is continued and repeated until constant weight 0.0001g or 0.1mg is obtained as inorganic ash. Application:Ignition is used for standardization and purification of chemical compounds e.g. Zn ointment on ignition leaves only ZnO. This process is also used to determine the sulphated ash in which ignited substance is H2SO4. This process has limited application but

Trituration

This method is applied when the medicament is solid and insoluble in base. So for this purpose solids are finely powdered and passed through a sieve of appropriate size.

Trituration may be carried out with an ointment tile and spatula or using a mortar and pestle.

Trituration using tile and spatula

Small quantities of finely powdered solids may be mixed on a tile by means of a spatula.Tiles are usually made of glass and should be large enough for the quantity of powder to be mixed or ointment to be prepared. Usually for small scale work 300mm square is a useful size for a tile.Spatula is made of stainless steel except for the few medicaments those react with stainless steel (iodine), should be flexible and long blade (25mm by200mm) to provide a large rubbing surface. Powders for Trituration are placed on the tile and gently mixed until the mixture is smooth and homogeneous, but in the case of ointment if base is very soft it may be helpful to warm the tile but overheating should be avoided because the base will become too fluid for efficient levigation and may run off the edge of the tile. The dispersion is then diluted with increasing amount of base, doubling the quantity each on the tile of each dilution. Finally any liquid ingredient is incorporated.

Trituration using mortar & pestle

A mortar should be used when the quantities are too large to be conveniently dealt with tile. A mortar with a fairly flat base and a pestle with a flat head will give best results.It is impossible to ensure intimate dispersion of one powder in another by mixing the two substances all at once. The purpose is to add a substance that is present in greater amount to the whole of the substance present in lesser amount. Substance present in greater amount is introduced into the mixture in very small quantities at first, but gradually increasing the quantities, until the whole of the substance has been added.. In the case of ointments, the sequence of mixing is same as in the tile method, powders are mixed and then gradually incorporated into the base and finally any liquid ingredients are added.

Levigation

For aqueous suspensions the material is made into a paste with the vehicle and ground in a mortar. Effort put in while the paste is thick, before the addition of more vehicle produces most effects.

For semisolid preparations the medicament is rubbed down with the warm base on a warm tile or in a warm mortar.

6-Elutriation:

Definition: Elutriation is the process in which the particles of the fluid move in a direction opposite to that of the sedimentation. (Downward movement)

Explanation: In gravitational sedimentation the particles will move vertically downward while the fluid travels vertically upward. If the velocity of the fluid is less then the setting velocity of the particles, then the particles will move downward against the stream of fluid. If the setting velocity of particles is less then the velocity fluid, the particles will move upward. In other words small size particles will move upward while the large size particles will move downward. So Elutriation is the process of separation of fine particles from course particles. The particles size can also be measured by this process. The air Elutriation usually give shaper fractions of small and large particles then water Elutriation.

Apparatus used for ElutriationThe apparatus used for Elutriation process is called as Elutriator. They are of two types:Gravitational ElutriationCentrifugal Elutriation

Gravitational Elutriation1- Gravitational Elutriation:In gravitational Elutriation the fluid particles move downward due to sedimentation (force of gravity) while the lighter particles remain upward.

Centrifugal Elutriation:

Centrifugal Elutriation causes the fluid stream to rotate under high centrifugal force to suspend the particles. These particles which are too large to rotate with direction of flow of fluid, separates out on the wall of the elutriator. However the fine particles move easily with the stream of fluid. Centrifugal Elutriator is again of two types:Darrclone classifier.Sharp less super classifierThe sharp less super classifier is useful for high speed separation of fine particles. It has a capacity of 250lb/hr and operates on air flow of about 100 cubic feet/min at maximum speed of about 50,000 rpm.

Uses of ElutriationHeavy and light Kaolin can be separated by this process, because the particles of heavy Kaolin move downward and those of the light Kaolin move upward. 5g of kaolin is taken with 70mL of water containing sodium pyrophosphates. After 5 minutes sedimentation, 50mL is withdraw and the process is repeated with addition of 50mL of water, until 400mL is removed (8 times withdraw 50mL) to obtain 0.025g of dry Kaoline.