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Dyes and Drugs


Dyes are the natural or synthetic coloured substances, which are used in imparting colour to textiles, silk, wool, foodstuff, leather etc.

Characteristics of dyes:
All coloured substances are not dyes. A dye should have following characters:
a. It must be a coloured compound that can be firmly fixed to a fabric from its solution directly or with the help of mordant.
b. Once fixed to the fabric, it should be inert to light and resistant to washing, heat and bleaching.

A dye is made up of two parts:

1. Chromophores: [Grk: Chroma – colour, Phoros – bearer]

They are the unsaturated groups responsible for the colour of the dye.

Examples: Nitro group (–NO2), Azo group (–N=N–), Nitroso group(–N=O), etc.

2. Auxochromes: [Grk: auxo – increase, chroma – colour]

They are the colour intensifying groups which do not impart colour in absence of chromophores. 

Examples: Acidic ; -OH, -SO3H, -COOH

Basic : -NH2, -NHR, -NR2

Neutral : -OR

The polar auxochromes make a dye water soluble and binds it to the fabric.

Types of Dyes:

A] Natural dyes:

These are the dyes obtained from animal and vegetable sources.







Flowers of colour thistle (a type of flower)



Leaves of indigo plant



Madder roots

Tyrian purple


Snail (Murex Brandaris)

B] Synthetic dyes:

These are the dyes prepared in the lab by artificial means.

Examples: p-amino azobenzene, p-hydroxyazobenzene, etc.

1. Azo dye: The dye having a chromophore unit azo group (–N=N–) is called azo dye.


They are used as dyes for oil and lacquers.

It is used as an indicator.

2. Phthalein dye: Its chromophore unit is


It is used as an indicator.

3. Nitro dye: Its chromophore unit is


It is used as dye for wool.

On the basis of method of application, dyes are of different types:

1. Direct dyes: - These are water soluble dyes and fabric is directly immersed into their aqueous solution. It is better for the fabric which can form hydrogen bonds with the dyes.
Example:- Martius yellow


2. Vat dyes:- These insoluble dyes are reduced into colourless compounds by sodium hydrosulphite in large vat. The reduced dye is water soluble into which clothes are immersed and air oxidized while drying. The colourless compound is oxidized back into insoluble dye which is firmly fixed into the fabric.
Examples:- Indigo and anthraquinone.

3. Mordant dyes: - These are the dyes which are applied to the fabrics with the coordination of salts of metals like Al, Cr, Ba etc called mordants.  Example: Alizarin.

4. Azoic or ingrain dyes: - These are the dyes synthesized within the fabrics, especially the azo dyes.
The fabric is immersed into the solution of coupling reagents like phenol, naphthol etc followed by the immersion into the solution of appropriate diazonium salt. Water insoluble azo dye is fixed into the surface of fabric.


Drugs are the chemical substances which exert various physiological effects of therapeutic values. They are the chemicals used in medicines.

Characteristics of Drug:

  1. An ideal drug should be localized at the site where it is desired to act.

  2. It should have minimum side effects.

  3. It should be non-toxic and efficient.

  4. It should not injure the physiological process or host tissues.

  5. It should not make the host cell resistant to the drug after the use for some time.

Drugs are of the two types of the basis of their therapeutic action:

A] Pharmacodynamic Agents: They have effects in organisms but are not specific remedies for the particular diseases.

Examples: (i) Antipyretics (ii) Analgesics (iii)Analgesics & Antipyretics (iv) Anesthetics 

(v) tranquilizers (vi) Antidepressants etc.

B] Chemotherapeutic Agents: They are used in treatment and cure of specific diseases. Examples: (i) Antibiotics (ii) Antiseptics (iii) Anti-Fungal (iv) Antiprotozoal etc. 

1. Antipyretic Drugs: These are the drugs used for reducing fever.
Examples: Paracetamol, Methacetin etc.

2. Analgesic Drugs: These are the drugs which relieve all sorts of pains without loss of consciousness and are commonly called painkillers. Examples: Novalgin, Melubrina, etc.

 3. Analgesics and Antipyretics: These are the drugs which are used to reduce body temperature as well as relieve pains. Examples: Aspirin, Phenacetin, Aminopyrene etc.

 4. Antiseptics: These are the drugs which kill or prevent the growth of microorganisms.


 i) Tincture of Iodine (alcoholic solution of I2)

ii) Iodoform (CHI3)

iii) Iodol (tetraiodo pyrrole)
iv) Chloroxylenol 

Dettol is a mixture of chloroxylenol and terpineol in alcohol.

5. Antibiotics: These are the drugs derived from certain microorganisms which inhibit the growth of or kill some other microorganisms.

i) Broad spectrum antibiotics: They are general and act against several microorganisms

Examples: - Chloramphenicol/ chloromycetin (effective to cure typhoid, pneumonia, meningitis etc.), tetracycline etc.

ii) Narrow spectrum antibiotics: They are highly specific to kill particular microorganism Examples: penicillin (effective in treatment of pneumonia), streptomycin etc.

6. Tranquilizers: They are used to treat mental disorders. They reduce anxiety and tension and restore the peace of mind. Sedatives like Diazepam and Equanil do not induce sleep whereas Hypnotics induce sleep.

7. Anaesthetics: These are the drugs which induce insensitivity.

(a) General or central Anaesthetics: They cause overall unconsciousness of the body.
Examples: Chloroform, nitrous oxide, cyclopropene, ethylene etc.
(b) Local Anaesthetics: They cause loss of sensation in a particular small body portion.
Examples: Cocaine, Ethyl chloride etc.

8. Sulpha drugs:

They are the chemically synthesized (not from microorganisms) drugs acting as antibiotics. The parent drug is sulphanilamide.

Examples: Sulpha drugs are sulphaguanidine, sulphathiazole, sulphadiazine etc.

Drug addiction:

Compulsive physiological need for a habit forming drug such as heroin, morphine, cocaine, etc is called drug addiction. These produce a false feeling of happiness, peace and tranquility ultimately leading to physical and mental sickness. 

Once a person becomes addicted, the long term drug use causes severe physiological disorders like constipation, nausea, vomiting, respiratory depression etc. it causes serious problems in health, wealth, family and society. 


It can be carried out by withdrawal of the drug addict from the drug in a rehabilitation centre under medical supervision.

Alternatively, other less effective types of drugs can be substituted. For example, Methadone instead of morphine.

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