Absorption Spectra of Mixed Liquids. 473 



that is, toward the part absorbed by the sulphate. The posi- 

 tion of the bands with the carmine solution alone was meas- 

 ured frequently. The mean of from nine to twelve observa- 

 tions at different strengths gave : displacement due to simple 

 superposition, 2"2' | and , 4 / ; additional displacement due to 

 mixture, 5' and 7*5 / . The displacements due to mixture 

 varied from -V to 12' for different strengths of the sulphate, 

 and seemed in many cases to increase as the mixed liquids 

 were allowed to stand. In some instances a flocculent precipi- 

 tate was formed. As in the case of the carmine and bichro- 

 mate, the displacement did not decrease gradually as the sulphate 

 was diluted, but at a certain stage of dilution disappeared 

 almost entirely. In the case of the copper sulphate and car- 

 mine this occurred when the ratio of the two substances by 

 weight was about unity. 



Fuchsin and aniline blue in alcohol were next tried, but the 

 effect of mixture was the same as that of simple addition. 

 With fuchsin and picric acid the fuchsin band either disap- 

 peared altogether on mixture or was much weakened and 

 blurred at the edges. With a mixture of aniline blue and 

 picric acid, the aniline band was much widened and perhaps 

 shifted toward the blue. These substances were all tried by 

 Prof. Melde. In the case of the aniline substances last tried, 

 the writer's experiments indicate that Melde's results were due 

 to simple addition, but in the case of the others an actual and 

 very considerable motion of the narrow band toward the wide 

 absorption area is indicated. 



The writer hopes that he may be able rigorously to investi- 

 gate the laws of this displacement at some future time, deter- 

 mining the substances which have on each other a real effect 

 of the kind mentioned, and the dependence of the effect on 

 the ratio of the substances, their temperature, and the time 

 after mixture. With regard to the sudden diminution of the 

 displacement at a certain stage of the dilution, it is easily un- 

 derstood if we suppose that the influence of the molecules, 

 in producing the effect we view as a displacement of absorp- 

 tion bands, is proportional to a higher inverse power of their 

 distances than the square, and that when those of one sub- 

 stance largely outnumber those of the other the more numer- 

 ous are arranged in clusters about each of the others. Then 

 dilution at first may have merely the effect of removing the 

 outer members of these clusters, whose effect on the displace- 

 ment is small, but when the inmost layer of the cluster is 

 reached the case is different, and the effect of dilution shows 

 itself at once. Our ignorance of the state of a physical mole- 

 cule in solution prevents the direct test of this hypothesis by 

 experiment. 



