42 KANSAS ACADEMY OF SCIENCE. 



The excess of blue and violet in this case, if such existed, was certainly very much 

 less marked than in the adulterated whites already mentioned. The thick portions 

 of the same film which were accepted by the eye as being of unusually pure white- 

 ness, showed the influence of the absorption of the shorter wave-lengths, and the 

 absorption spectrum of the same portion possesses a curve in which the red end of 

 the spectrum is at least thirty times brighter than the region midway between the 

 G and H line. 



It seems evident, from this result, that we have to do in the antimony film with 

 a so-called subjective blue; with a color, in other words, which does not arise from 

 any marked excess of violet rays; and I believe the antimony film to be in this re- 

 spect typical of a very large class, viz., of all opalescent media. I am aware that 

 this view is not in accordance with those generally held concerning opalescence, it 

 being generally supposed that in such substances the incident ray is selectively di- 

 vided into two components, one of which, containing an excess of the longer wave- 

 lengths, gives the film its ruddy appearance when viewed by transmitted light, while 

 the blue appearance by reflected light is to be ascribed to the quality of the reflected 

 rays.^ 



It is commonly maintained that the particles of which such films are composed 

 reflect blue light and transmit the red because of their small size. I have long re- 

 garded this explanation as unsatisfactory, and the analysis of the reflexion and ab- 

 sorption spectra just described, which constitutes, I believe, the first attempt to 

 measure spectrophotometrically the light reflected and transmitted by an opalescent 

 medium, afifords us evidence that these substances reflect all visible rays equally well, 

 absorb the shorter wave-lengths, and transmit a corresponding excess of red light. 



I have assured myself, moreover, by an inspection of the antimony films under 

 the microscope, with properly-managed illumination from above, that the particles 

 of those portions of an antimony film which appear blue to the unaided eye, though 

 small, are capable of reflecting white light. Under such circumstances all traces of 

 blue vanish, and the field of view shows the particles of antimony oxide, of a pure 

 white, very sparsely distributed upon a black background. These particles, which 

 are readily measured by means of the eye-piece micrometer, vary in diameter from 

 .0007 millimeters to .0015 millimeters; and portions of the same film, when thick 

 enough to appear perfectly white to the naked eye, present in the microscope a 

 field in which the particles are of the same sizes and of the same individual appear- 

 ance, but in which the number per unit of area is much greater. 



The hypothesis that the differences of color in such films are due to differences 

 in the size of particles, can, moreover, be disposed of by the following very simple 

 but conclusive experiment: If antimony be burned in the flame of a blast lamp and 

 a piece of smoked glass or charcoal be exposed for an instant to the fumes, the thin 

 film first formed will present the color usually obtained before the blowpipe, and it 

 may be converted into the white film by a longer exposure. In this case, the change 

 of color is produced by the accumulation of the same particles which, at the begin- 

 ning of the experiment, went to build up the blue film, and the change in appear- 

 ance cannot be ascribed to any arrangement in order of sizes upon different portions 

 of the glass, but is evidently due to the increasing thickness of the deposit. 



A spectrophotometric analysis of the opalescent solution produced by precipi- 

 tating sulphur from a solution of hyposulphite of soda gave results similar to those 

 obtained with the antimony film. The sulphur precipitate, as is well known, pre 

 sents by reflected light, in its incipient stages, a blue color quite as striking as that 

 of the antimony film. This changes to a milky white as the precipitate becomes 



' See C. H. Kayle, Am. Journal of Science. 



