230 PHYSIOLOGICAL CHEMISTRY. 



intervals as needed. By this means the collagen is transformed and 

 a body known as gelatin is produced (see p. 228). 



3. Gelatin. On the gelatin formed from the transformation of 

 collagen in the above experiment (g), or on gelatin furnished by the 

 instructor make the following tests: 



(a) Solubility. Try the solubility in the ordinary solvents (see 

 page 23) and in hot water. 



(b) Milloris Reaction. 



(c) Hopkins-Cole Reaction. Conduct this test according to 

 the modification given on page 101. 



(d) Test for Loosely Combined Sulphur. 



Make the following tests upon a solution of gelatin in hot water : 



(a) Precipitation by Mineral Acids. Is it precipitated by strong 

 mineral acids such as concentrated hydrochloric acid? 



(b) Salting-out Experiment. Saturate a little of the solution 

 with solid ammonium sulphate. Is the gelatin precipitated? Re- 

 peat the experiment with sodium chloride. What is the result? 



(c) Precipitation by Metallic Salts. Is it precipitated by metal- 

 lie salts such as cupric sulphate, mercuric chloride and plumbic 

 acetate ? 



(d) Coagulation Test. Does it coagulate upon boiling? 



(e) Precipitation by Alkaloidal Reagents. Is it precipitated 

 by such reagents as picric acid, tannic acid and trichloracetic acid? 



(/) Biuret Test. Does it respond to the biuret test? 



(g) Bardach's Reaction. Does it yield the typical crystals of 

 this reaction-? (See page 94.) 



(h) Precipitation by Alcohol. Fill a test-tube one-half full of 

 95 per cent alcohol and pour in a small amount of concentrated 

 gelatin solution. Do you get a precipitate ? How would you pre- 

 pare pure gelatin from the tendo A chillis of the ox? 



II. YELLOW ELASTIC TISSUE (ELASTIN). 



The Ligamentum nuchce of the ox may be taken as a satisfactory 

 type of the yellow elastic connective tissue. The principal solid 

 constituent of this tissue is elastin, a member of the albuminoid 

 group. In common with the keratins and collagen, elastin is an 

 insoluble body and gives the protein color reactions. It differs 

 from keratin principally in the fact that it may be digested by 

 enzymes and that it contains a very small amount of sulphur. 



