CH. VI.] MICRO-SPECTROSCOPE AND POLARISCOPE. 135 



dissolve them in the same medium. If all the reactions are identical 

 then the presumption is very strong that the bodies are identical or 

 very closely related. For example, while one might be in doubt be- 

 tween a solution of oxy- or CO-hemoglobiu and carmine, the addition 

 of ammonium sulphide would serve to change the double to a single 

 band in the O-hemoglobin, and glacial acetic acid would enable one to 

 distinguish between the CO-blood and the carmine, although the am- 

 monium sulphide would not enable one to make the distinction. 

 Furthermore it is unsafe to compare objects dissolved in different 

 media. The same objects as " cyanine and aniline blue dissolved in 

 alcohol give a very similar spectrum, but in water a totally different 

 one." " Totally different bodies show absorption bauds in exactly the 

 same position (solid nitrate of uranium and permanganate of potash in 

 the blue)." (MacMuun). The rule given by MacMuun is a good 

 one : " The recognition of a body becomes more certain if its spectrum 

 consists of several absorption bands, but even the coincidence of these 

 bands with those of another body, is not sufficient to enable us to infer 

 chemical identity ; what enables us to do so with certainty is the fact : 

 that the two solutions give bands of equal intensities in the same parts of 

 the spectrum which undergo analogous changes on the addition of the 

 same reagent.' " 



REFERENCES TO THE MICRO-SPECTROSCOPE AND SPECTRUM ANALYSIS. 



The micro-spectroscope is playing an ever increasingly important role in the 

 spectrum analysis of animal and vegetable pigments, and of colored mineral and 

 chemical substances, therefore a somewhat extended reference to literature will be- 

 given. Full titles of the books and periodicals will be found in the Bibliography 

 at the end. 



Angstrom, Recherches sur le spectre solaire, etc. Also various papers in period- 

 icals. See Royal Soc's Cat'l Scientific Papers ; Anthony & Brackett ; Beale, p. 

 269 ; Behrens, p. 139 ; Kossel und Schiefferdecker, p. 63 ; Carpenter, p. 104 ; Brown- 

 ing, How to Work with the Spectroscope, and in Monthly Micr. Jour., II, p. 65 ; 

 Dauiell, Principles of Physics. The general principles of spectrum analysis are 

 especially well stated in this work, pp. 435-455 ; Davis, p. 342 ; Dippel, p. 277 ; 

 Frey ; Gamgee, p. 91 ; Halliburton ; Hogg, p. 122 ; also in Monthly Micr. Jour., 

 Vol. II, on colors of flowers ; Jour. Roy. Micr. Soc, 1880, 1883, and in various other 

 vols.; Kraus ; Lockyer ; M'Kendrick ; MacMunn ; and also in Philos. Trans. R. S., 

 1886 ; various vols, of Jour. Physiol. ; Nageli und Schwendener ; Proctor ; Ref. 

 Hand-Book Med. Sciences, Vol. I, p. 577, VI, p. 516, VII, p. 426 ; Roscoe ; Schel- 

 len ; Sorby, in Beale, p. 269 ; also Proc. R. S., 1874, p. 31, 1867, p. 433 ; see also 

 in the Scientific Review, Vol. V, p. 66, Vol. II, p. 419. The larger works on Physi- 

 ology, Chemistry and Physics may also be consulted with profit. 



Vogel, Spectrum analysis, also in Nature, Vol. xix, p. 495, on absorption spectra. 

 The bibliography in MacMunn is excellent and extended. 



