236 



residue should be powdered as finely as possible with a minute 

 quantity (trace) of sodium chloride. A little of the powder is 

 then placed on a slide and covered with a slip under which some 

 glacial acetic acid is now run in. It is then warmed carefully to 

 a temperature just short of that which would cause the acid to 

 boil. If the operation has been successful, on cooling crystals of 

 haemin will be seen under a microscope, mixed in either case as in 

 Fig. 38 with a granular ddbris. If they are absent, warm again, 

 adding more acid if necessary. The crystals are dark-brown, fre- 

 quently almost black, elongated rhombic plates and prisms be- 

 longing to the triclinic system. 1 In a purified specimen they are 



FIG. 39. H.EMIN CRYSTALS. (After Preyer.) 



arranged singly or in groups as shown in Fig. 39, and apart from 

 their form are characterised by being strongly doubly-refracting : 

 when examined under the microscope between crossed Nicol 

 prisms those crystals whose axes are suitably inclined to the in- 

 cident light stand out bright yellow or orange on the dark field. 2 

 They are quite insoluble in either water, alcohol, ether, chloro- 

 form, or dilute acids : they may however be dissolved to some 

 extent in glacial acetic or hydrochloric acids, especially if 

 warmed, and are readily soluble in alkaline carbonates or dilute 

 caustic alkalis, being at the same time decomposed by the latter 

 solvent into haematin and a chloride of the alkali. This fact pro- 

 vides the best means for obtaining pure haematin (see above). 



Although it is quite easy to obtain typical crystals under the 

 microscope from minute amounts of haemoglobin or haematin, their 

 preparation on a large scale is somewhat tedious ; several methods 



1 Lahorio. Quoted by Schalfejew, Jn. d. rttss. phys.-chem. Gesell. 1885, S. 30. 

 See Abstr. in Ber. d. d. chem. Gesell. Bd. xvni. Ref., S. 232. Cf. Hogyes, Centralb. 



/. d. med. Wiss. 1880, No. 16. 



2 A. Ewald, Zt.f. Biol Bd. xxir. (1886), S. 474. 



