# Beer August

In 1852, Beer published a paper on the absorption of red light in coloured aqueous solutions of various salts. Beer makes use of the fact, derived from Bouguer’s and Lambert’s absorption laws, that the intensity of light transmitted through a solution at a given wavelength decreases exponentially with the path length d and the concentration c of the solute (the solvent is considered non-absorbing). Actually, the “Absorption Coëfficient” defined by Beer in his paper is the transmittance (or transmission ratio), $T=\frac{I}{I_{0}}$. Thus, as pointed out by Beer, the transmittance of a concentrated solution can be derived from a measurement of the transmittance of a dilute solution (Beer, 1852).
Beer’s law (Beer's Law and Beyond), also called Lambert–Beer law or Beer–Lambert law, in spectroscopy, is the physical law stating that the quantity of light absorbed by a substance dissolved in a nonabsorbing solvent is directly proportional to the concentration of the substance and the path length of the light through the solution. Beer's law is commonly written in the form $\ A=log_{10}\frac{I(0)}{I(L)}=\varepsilon c L\$, where $A$ is the absorbance, $c$ is the concentration in moles per liter, $L$ is the path length in centimeters, and ε is a constant of proportionality known as the molar extinction coefficient. The law is accurate only for dilute solutions; deviations from the law occur in concentrated solutions because of interactions between molecules of the solute, the substance dissolved in the solvent.