214 UNCONSCIOUS NERVOUS OPERATIONS 



EXPERIMENTS 



Food Elements. Some very interesting and easily performed 

 experiments may be made upon substances common in ordinary food. 



91. Tests for Proleids. To one fourth of a test tube of dilute white 

 of egg 1 (a proteid) add a few drops of strong nitric acid and boil. 

 Cool and add a little ammonia; the yellow color changes to orange. 

 To show that the orange color is due to the presence of a proteid, 

 repeat the experiment, using pure water instead of white of egg. 

 Another test is as follows : To one fourth of a test tube of a 15 per 

 cent solution of caustic soda add two or three drops of a 1 per cent 

 solution of copper sulphate. Shake the mixture, and after warming 

 add a little white of egg or other solution of proteid ; the blue color 

 becomes violet. To show that these color changes are tests for pro- 

 teids, repeat the above experiments, using a solution of sugar and the 

 starch solution mentioned below, instead of the white of egg. 



92. Coagulation of Albumin by Heat. Boil dilute white of egg in a 

 test tube; it does not clot. Then add, drop by drop, dilute acetic 

 acid (2 per cent) ; a precipitate of coagulated albumin finally sepa- 

 rates. If the white of egg is not diluted, it coagulates, of course, on 

 boiling. 



93. Solubility of Starch. Stir some starch into cold water and 

 observe that it does not dissolve. Boil the mixture ; solution occurs, 

 but the liquid remains somewhat cloudy. 



94. Test for Starch. To some of the starch solution prepared 

 above, add a drop of iodine solution. The blue color resulting is the 

 characteristic reaction of iodine with starch. Dilute the starch solu- 

 tion and repeat the experiment. The dilution may be much pro- 

 longed before the blue color fails to appear on adding iodine. To 

 show that the blue color is related to the presence of starch, add 

 iodine to pure water or any liquid from which starch is known to be 

 absent. 



95. Microscopical Examination of Starch. Scrape the fresh cut -sur- 

 face of a potato, and mount in water on a slide some of the material 

 thus obtained. Examine with the compound microscope. Numerous 



1 To prepare dilute white of egg, beat up the white of an egg with 

 about twenty volumes of water, filter through muslin, and pour off 

 gently to remove air bubbles present. 



