Abstract

To state that a substance fails to obey Beer’s Law is an injustice, since it is the investigator who has failed to make proper use of the Law. If the substance becomes a mixture of substances when in solution, Beer’s Law must be applied to each component of the mixture. It does not seem to be generally realized that this can often be done, even when none of the components of the mixture can be isolated in the pure state.

© 1948 Optical Society of America

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Figures (4)

Fig. 1
Fig. 1

Spectral transmittance curves of two mixtures, M1 and M2, of dyestuffs A and B in different proportions.

Fig. 2
Fig. 2

Spectral density curves of the mixtures whose spectral transmittance curves are shown in Fig. 1.

Fig. 3
Fig. 3

Spectral transmittance curve of a solution of dyestuff B. The circled points at wave-length intervals of 20 mμ were calculated from the spectral density curves of Fig. 2. The slight disparity in the region of short wave-lengths may be due to the fact that dyestuff B does not form a true solution.

Fig. 4
Fig. 4

Spectral transmittance curve of a solution of dyestuff A. The circled points at wave-length intervals of 20 mμ were calculated from the spectral density curves of Fig. 2.

Equations (7)

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D 1 = a 1 D a + b 1 D b ,
D 2 = a 2 D a + b 2 D b .
F = D 2 - k D 1 = ( a 2 - k a 1 ) D a + ( b 2 - k b 1 ) D b .
d 2 F / d λ 2 = d 2 D 2 / d λ 2 - k d 2 D 1 / d λ 2 .
k = d 2 D 2 d λ 2 / d 2 D 1 d λ 2 ,
k = 0.076 / 0.113 = 0.675.
D b = F 1 - k = F 1 - 0.675 = 3.08 F .