H^MATIN. 251 



concentrated hydrochloric acid, at a temperature above 150 0. Con- 

 centrated sulphuric acid dissolves it, without any gas being evolved, 

 giving rise to a dark red solution, from which water precipitates the 

 substance known as " hsematoporphyrin " (see p. 258), which, as it 

 contains no iron, has been sometimes spoken of as iron-free hsematin. 

 This body is soluble in alkaline solutions, and both its acids and 

 alkaline solutions exhibit very characteristic absorption-spectra. 



Alkaline solutions of hsematin in thick layers, when examined by 

 transmitted light, appear red, whilst thin layers appear of an olive- 

 green colour. Acid solutions, whatever the thickness of the stratum 

 examined, always appear of a brown colour. 



When the spectrum of light transmitted through alkaline and acid 

 solutions of hgematin is examined by the photographic as well as by the 

 direct method, it is seen that the last rays of the spectrum to be 

 absorbed are the red rays up to B ; that the solutions are characterised 

 by a denned absorption-band between C and D, which is shifted towards 

 D in the case of the alkaline, towards C in the case of the acid solutions ; 

 that alkaline solutions, even when extremely diluted, effect a general 

 absorption of the whole ultra-violet, violet, etc., rays ; that acid solutions, 

 even when very highly diluted, whilst not exerting a general absorption 

 of the ultra-violet, exhibit an absorption-band at the junction of the 

 extreme violet and the ultra-violet, properly so called. 



The absorption-bands in the visible spectrum of both alkaline and 

 acid solutions of hsematin are shown in Plate II., Spectra 2, 4, and 6. 

 The alkaline solutions exhibit one absorption-band between C and D, of 

 which the more refrangible border adjoins D, whilst acid solutions exhibit 

 an absorption-band also between C and D, of which the less refrangible 

 border adjoins C, though the position of the band is somewhat in- 

 fluenced by the particular acid which has been employed. Attention 

 is directed to the fact that the band between C and D in the spectrum 

 of methsemoglobin differs in position from the band in the spectrum 

 of acid as well as from that of alkaline haematin. Whilst the absorption- 

 band of the former is close to C and that of the latter close to D, the 

 band of methsemoglobin, in acid solutions, is separated by a marked 

 interval Loth from C and I), though it is closer to the former than to 

 the latter. 



Alkaline solutions of hsematin in the presence of certain foreign 

 matters, when treated with reducing agents, exhiLit a spectrum which 

 is apparently identical with that which will Le described under " Hsemo- 

 chromogen," and which was first described by Stokes as the spectrum of 

 reduced hcematin. The band in the red disappears, and two characteristic 

 bands appear in the green (Plate II., Spectrum 3). On now shaking 

 the reduced liquid with air, the two bands first referred to disappear, 

 and are replaced by the original hsematin band. 



This experiment would appear to show that hsematin is but oxidised hsemo- 

 chromogen, a conclusion which is false, and which is an illustration of the 

 mistakes into which observers may be led who conclude as to the identity of 

 two colouring matters from the identity of prominent absorption-bands in their 

 spectra. 



A strong proof that oxidised hsemochromogen is not identical with hsematin. 

 is derived from my own observations on the absorption of the extreme violet and 

 ultra-violet. Whilst hsematin possesses even in solutions of great dilution the 

 power of absorbing the whole of the ultra-violet, the violet and even the blue 



