SUGGESTIONS FOR LABORATORY WORK 589 



After forty minutes pour the mixture into a dish containing 100 c. c. 

 water. Drive off the alcohol by heating over water. While still 

 hot acidify with sulphuric acid. On cooling the fatty acid forms 

 a solid crust on the surface of the liquid. Remove it. The glycerin 

 is dissolved in the liquid. 



The fatty acid is insoluble in water as may be shown by test. 



Saponification. Soap is a compound of fatty acid with alkali. 

 Shake some of the fatty acid produced above with warm dilute 

 caustic soda. Filter. The filtrate shows the characteristic features 

 of a soap solution. Soaps form an insoluble compound with calcium 

 chlorid. This can be shown by adding a few drops of calcium 

 chlorid to some of the soap solution in a test tube. Hard water 

 contains calcium salts. This explains the difficulty of using soap 

 with hard water. 



Proteins. Tests for Proteins. Raw egg white is a satisfactory 

 protein for these tests. 



Heat Test. To a small amount of a solution of protein add a 

 drop of a two-tenths per cent solution of acetic acid. Heat the 

 upper portion of the solution. The protein is rendered insoluble 

 and is now a coagulated protein. 



Biuret Test. To a solution of protein add a drop or two of a 

 one per cent solution of copper sulphate (CuS0 4 ) and then strong 

 sodic hydrate (NaOH). A characteristic violet color is the test. 



Xanthoproteic Reaction. To a solution of protein add a few drops 

 of strong nitric acid (HNO 3 ), and boil; after cooling, add ammonic 

 hydrate (NH 4 OH). A yellow color which deepens to orange when 

 the ammonia is added is the test. 



Physico-Chemical Principles. Osmosis. Tie an osmotic mem- 

 brane (gold beater's skin, bladder) across the mouth of a funnel 

 or thistle tube. Fill with a sugar solution of the consistency of 

 syrup. Attach a glass tube to the nozzle of the funnel. Fasten in 

 an upright position and surround the funnel with distilled water 

 in a beaker. 



Drops of blood on a microscope slide may be used to demonstrate 

 losis indirectly. Three such drops should be examined; one 

 diluted with distilled water; a second with 0.9 per cent sodium 

 chlorid ; the third with 10 per cent sodium chlorid. Avoid excessive 

 evaporation. The destruction of the corpuscles in the dilute solu- 

 tion by over-distension (plasmolysis) ; their preservation in the 0.9 



