A calorimeter is a device used to measure heat that consists of a metallic vessel with a stirrer inside an insulating jacket. There are different types including adiabatic, reaction, bomb, and differential scanning calorimeters. Beer's law and Lambert's law state that absorbance is directly proportional to concentration and path length, respectively. In 1852, Beer discovered absorbance is also proportional to concentration. The Beer-Lambert law equation relates absorbance, molar absorptivity, concentration, and path length. Beer-Lambert law has applications in fields like spectrophotometry, atmospheric analysis, chemistry, and analyzing mixtures. It describes how light absorption relates to material properties through

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.