i86 



PHYSIOLOGICAL CHEMISTRY 



(b) Solubility. Try the solubility of glycerol in water, alcohol and ether. 



(c) Hypochlorite-Orcinol Reaction. 1 This is based on the oxida- 

 tion of glycerol to the corresponding aldose sugar glycerose and the 

 detection of the latter by means of orcinol. Homologues of glycerol 

 as well as the corresponding acids and certain sugars as glucose and 

 mannose give the reaction. The first named occur seldom while the 

 latter may be removed with baryta. 



Two to 3 c.c. of a i per cent or o.i per cent solution of glycerol in water is 

 treated with exactly 3 drops ( = 0.12 c.c.) normal NaOCl 2 and boiled for a minute. 

 To the liquid while still hot add 3 drops of hydrochloric acid (sp. gr. 1.124) and 



boil 30-60 seconds to drive off chlorine, a 

 colorless solution being obtained. Then add 

 an equal volume of fuming hydrochloric acid and 

 a small knife-point of orcinol. On boiling the 

 mixture becomes a beautiful violet or green blue. 

 The precipitate formed is soluble in amyl alcohol 

 and may be examined spectroscopically. 



(d) Acrolein Test. Repeat the test as given 

 under 4, page 183. 



(e) Borax Fusion Test. Fuse a little 

 glycerol on a platinum wire with some powdered 

 borax and note the characteristic green flame. 

 This color is due to the glycerol ester of boric 

 acid. 



(f) Fehling's Test How does this result 

 compare with the results on the sugars? 



(g) Solution of Cu(OH) 2 . Form a little 

 cupric hydroxide by mixing copper sulphate 

 and potassium hydroxide. Add a little glycerol 

 to this suspended precipitate and note what 

 occurs. 



13. Iodine Absorption Test. Dissolve a 

 small amount of an unsaturated organic acid, 

 e.g., oleic acid, in chloroform. Add 2-3 drops 

 of HiibPs iodine solution 3 and shake. The solu- 

 tion will be decolorized if unsaturated acids .are 

 present. This is due to the absorption of the 

 iodine. The test should be controlled by shak- 

 ing chloroform and iodine solution to which no 

 acid has been added. 



14. Melting-point of Fat. First Method. 



Insert one of the melting-point tubes, furnished by the instructor, into the 

 liquid fat and draw up the fat until the bulb of the tube is about one-half full 

 of the material. Then fuse one end of the tube in the flame of a Bunsen burner 



l Mandel and Neuberg: Bioch. Zeit., 71, 214, 1915. 

 2 Made according to Raschig: Ber., 40, 4586; 1907. 



1 Prepared by dissolving 26 grams of iodine and 30 grams of mercuric chloride in one 

 litre of 95 per cent alcohol. 



FIG. 60. MELTING-POINT 

 APPARATUS. 



