Beer and Lambert law

1. CALORIMETER

2. Calorimeter
◦ A calorimeter is a device used for heat measurements necessary for calorimetry.
◦ It mainly consists of a metallic vessel made of materials which are good conductors of electricity
such as copper and aluminium etc.
◦ There is also a facility for stirring the contents of the vessel.
◦ This metallic vessel with a stirrer is kept in an insulating jacket to prevent heat loss to the
environment.
◦ There is just one opening through which a thermometer can be inserted to measure the change
in thermal properties inside.

4. TYPES OF CALORIMETER
◦ Adiabatic Calorimeters
◦ Reaction Calorimeters
◦ Bomb Calorimeters (Constant Volume Calorimeters)
◦ Constant Pressure Calorimeters
◦ Differential Scanning Calorimeter

5. BEER AND LAMBERT LAW
◦ Beer’s law states the following:
◦
◦ For a given material, the sample path length and concentration of the sample are directly
proportional to the absorbance of the light.
◦ Beer law states that concentration and absorbance are directly proportional to each other and it
was stated by August Beer.
◦ Lambert law states that absorbance and path length are directly proportional and it was stated
by Johann Heinrich Lambert.

6. DISCOVERY OF BEER AND LAMBERT
LAW
◦ In 1729, Pierre Bouguer discovered the law.
◦ Later, in 1760, Johann Heinrich Lambert quoted Bouger’s discovery saying that the absorbance
of a sample is directly proportional to the path length of light. Although Lambert dint claim the
discovery, he was often credited with it.
◦ In 1852, August Beer discovered a related law which stated that the absorbance is proportional
to the concentration of the sample.

7. BEER AND LAMBERT LAW EQUATION
◦ The Beer-Lambert law equation is as follows:
◦ A = εLc
◦ A is the amount of light absorbed for a particular wavelength by the sample
◦ ε is the molar extinction coefficient
◦ L is the distance covered by the light through the solution
◦ c is the concentration of the absorbing species.

8. APPLICATIONS OF BEER AND LAMBERT
LAW
◦ This law finds applications in various fields such as:
◦ This analysis mainly concentrates on the separation, quantification, and identification of matter
by spectrophotometry.
◦ In atmosphere
◦ Solar or stellar radiation in the atmosphere can be detected
◦ The law is used in chemistry to measure the concentration of chemical solutions, analyse
oxidation, and measure polymer degradation.
◦ The Beer-Lambert law relates the attenuation of light to the material’s properties through which
the light is travelling. The law is applied to the analysis of a mixture by spectrophotometry
without extensive pre-processing of the sample.

9. Reference
1. Bouguer, Pierre (1729). Essai d’optique sur la gradation de la lumière [Optics essay on the
attenuation of light] (in French). Paris, France: Claude Jombert. Pp. 16
2. Lambert, J.H. (1760). Photometria sive de mensura et gradibus luminis, colorum et umbrae
[Photometry, or, On the measure and gradations of light intensity, colors, and shade] (in Latin).
Augsburg, (Germany): Eberhardt Klett.
3. Beer (1852). “Bestimmung der Absorption des rothen Lichts in farbigen Flüssigkeiten”
[Determination of the absorption of red light in colored liquids]. Annalen der Physik und
Chemie (in German). 162 (5): 78–88.
4. Pfieffer, Heinz; Liebhafshy, Herman (1951). “The Origins of Beer’s Law”. Journal of Chemical
Education (March, 1951): 123–125.
5. Mayerhöfer, Thomas G.; Pahlow, Susanne; Popp, Jürgen (2020). “The Bouguer-Beer-Lambert
Law: Shining Light on the Obscure”. ChemPhysChem. 21 (18): 2031.
doi:10.1002/cphc.202000464.