1892.] On Turacin, an Animal Pigment containing Cojp'per. 399 



largely taught, and fallaciously used, as a fundamental proposition in 

 thermodynamics. 



It is in truth, only for an approximately " perfect " gas, that is to 

 say, an assemblage of molecules in which each molecule moves for 

 comparatively long times in lines very approximately straight, 

 and experiences changes of velocity and direction in comparatively 

 very short times of collision, and it is only for the kinetic energy of 

 the translatory motions of the molecules of the " perfect gas," that the 

 temperature is equal to the average kinetic energy per molecule, as 

 first assumed by Waterston, and afterwards by Joule, and first proved 

 by Maxwell. 



II. " Researches on Turacin, an Animal Pigment containing 

 Copper : Part II." By A. H. Church, M.A., F.R.S., Pro- 

 fessor of Chemistry in the Royal Academy of Arts, London. 

 Received April 2, 1892. 



(Abstract.) 



This paper is in continuation of one read before the Society in 

 May, 1869.* It contains an account of observations made by other 

 investigators on turacin and on the occurrence of copper in animals ; 

 a table of the geographical distribution of the Touracas, and a list of 

 the twenty-five known species ; a chart of turacin spectra (for which 

 the author is indebted to the kindness of Dr. MacMunn) ; and a 

 further examination of the chemical characters and the composition 

 of turacin. The more important positions established by the present 

 inquiry are these : — 



1. The constant occurrence in eighteen out of the twenty-five known 

 species of Musophagidce of a definite organic pigment containing, as 

 an essential constituent, about 7 per cent, of copper. 



2. The " turacin-bearers " comprise all the known species of the 

 three genera, Turacus, Gallirex, and Musophaga, while from all the 

 species of the three remaining genera of the family MusopJiagidce, 

 namely, Gorythceola, Schizorhis, and GymnoscMzorhis, turacin is absent. 

 Furthermore, the zoological arrangement of the genera constituting 

 this family is in accord with that founded on the presence of turacin. 



3. The spectrum of turacin in alkaline solution shows, besides the 

 two dark absorption bands previously figured, a faint broad band on 

 either side of line F, and extending from X 496 to \475. 



4. The spectrum of isolated turacin in ammoniacal solution shows, 

 besides the three bands already named, a narrow fourth band, lying 

 on the less -refrangible side of line D, and extending from X 605 to 



* ' Phil. Trans.,' vol. 159, pp. 627—636. 



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