484 V. CHEMISTRY OF PHOSPHATIDES AND CEREBROSIDES 



cerebron, 30.7; cerasine (C48H93NO8H2O), 30.6; nervone, 62.7. The 

 specific rotation is also of use in determining the purity of the sample. 

 This latter criterion and the determination of the iodine number can, of 

 course, be used only if the amounts of material are relatively large. 



5. Properties of the Cerebrosides 



The cerebrosides in general exhibit similar chemical properties. They 

 are all white powders which are more or less wax-like; they separate from 

 alcohol in small particles which resemble crystal balls, but they probably 

 are not truly crystalline, although it is claimed that phrenosine has been 

 prepared in crystal form. Under certain conditions they form liquid 

 crystals, and this fact may account for discrepancies in the literature as to 

 the melting point. The cerebrosides are all insoluble in water, as is also 

 the case with diethyl ether and petroleum ether. On the other hand, pyri- 

 dine, acetone, chloroform, and acetic acid act as solvents, as does alcohol 

 to a lesser extent. All of the cerebrosides are optically active. None of 

 them reacts with nitrous acid, since in all cases the amino group is in com- 

 bination with the fatty acid residue. 



(1) Phrenosine 



Phrenosine is soluble in hot and cold pyridine and in hot solutions of 

 alcohol, benzene, acetic acid, ethyl acetate, acetone containing 10% water, 

 and chloroform. When the hot solutions are cooled, phrenosine is usually 

 precipitated in lumps which on drying appear more or less like cholesterol 

 crystals. 



The so-called liquid crystals were first described by Rosenheim. ^^^ 

 When some dry powder is heated until it is melted, on a slide in the Leh- 

 mann's polarization microscope, it becomes completely isotropic. On 

 cooling, numerous anisotropic, needle-like, liquid crystals appear. Such 

 crystals contain one molecule of water of crystallization, ^''^•^-^ which can be 

 removed in vacuo over sulfuric acid, as well as when heated to 105°C. 



On heating, phrenosine assumes a moist appearance at 130°C. and melts 

 at 212°C.'*" This property is explained on the assumption that it first 

 enters the liquid crystalline state and later the liquid state. At 95°C. it 

 begins to go into the anisotropic liquid state, and this is completed at 130°C. 

 The change from the liquid crystalline state to the liquid occurs at 212- 

 215°C.^^'''''-^ A marked decrease in viscosity results concomitantly. 

 This has been referred to as the "clearing point." 



When a fine aqueous suspension of phrenosine is heated, it shows a tend- 



"« O. Rosenheim, Biochem. ./., 8, 121-127 (1914). 



*'^ E. Worner and H. Thierfelder, Z. physiol. Chem., 30, 542-551 (1900). 



