13 



22. Make a watery solution of gelatin (.5%) by allowing 

 it first to swell up in the cold water, and then dissolving it 

 with the aid of heat. It is insoluble, but swells up in about 

 six times its volume of cold water. 



23. After dissolving with the aid of heat, allow a small 

 portion to cool ; it gelatinizes. 



24. Apply the xanthoproteic test for proteids to some of 

 the dissolved portion ; make notes of any differences as com- 

 pared with proteids in this and in the following tests : 



25. Use Millon's reagent. 



26. Try Piowtrow.ski's reaction. 



27. Is it precipitated by the acetic acid and potassium fer- 

 rocyanide test ? 



28. Does it coagulate by heat ? 



29. Is it precipitated by saturation with magnesium 

 sulphate ? 



30. What is the result of the addition of tannic acid ? 



31. Add picric acid (saturated .solution) ; if a precipitate 

 appears apply heat and note any change that may occUr upon 

 cooling. 



32. What is the effect of adding alcohol to the gelatin 

 solution ? 



IV. 



33. Carbohydrates. The term carbohydrates includes 

 an important group of substances, occurring especially in 

 plants. Starch and sugar make up a large proportion of the 

 parts of plants, while cellulose forms the chief material from 

 which many parts of plants are constructed. Carbohy- 

 drates also occur to a less extent in animals, where they are 

 represented chiefly by glycogen and some forms of sugars. 



In elementary composition they are non-nitrogenous and 

 consist of CH and O with the H and O in the same pro- 

 portion as in water, that is, 2 atoms of H to i atom of O. 



