THE SEED 9 



Experiment 3. To show the presence of starch. — Put a drop of 

 iodine solution on some starch. What change of color takes place ? To 

 make iodine solution, add to one part of iodine crystals 4 parts potas- 

 sium iodide and 95 parts water. It should be kept in the dark, as light 

 decomposes it. Iodine colors starch blue, protein substances light brown. 

 In testing for starch, the solution should be diluted till it is of a pale color, 

 otherwise the stain will be so deep as to appear black. 



Experiment 4. A test for proteins. — Place a small quantity of 

 the white of an egg, diluted with water, in a clean glass and add a few 

 drops of nitric acid ; or drop some of the acid on the white of a hard- 

 boiled egg. What is the effect ? 



Nitric acid turns proteins yellow ; if the color is indistinct, add a drop 

 of ammonia, when an orange color will ensue. 



Experiment 5. Another test for proteins. — Place on the sub- 

 stance to be examined a drop of a saturated solution of cane sugar and 

 water ; add a drop of pure sulphuric acid ; if proteins are present, they 

 will be colored red. See also Exp. 3. 



Experiment 6. A test for grape sugar. — Heat a teaspoonful of 

 Fehling's Solution to the boiling point in a test tube (a common glass vial 

 can be used by heating gradually in water) and pour in a few drops of 

 grape sugar solution. Heat again and observe the color of the precipitate 

 that forms. 



Fehling's Solution may be obtained of the druggist, or, if preferred, 

 it may be prepared in the laboratory as follows : (a) Dissolve 173 grams 

 of crystallized Rochelle salts and 125 grams of caustic potash in 500 cc. of 

 water; (6) dissolve 34.64 grams crystallized copper sulphate in 500 cc. 

 of water, and mix equal parts as needed. (For English equivalents, see 

 Appendix, Weights and Measures.) The two mixtures must be kept sep- 

 arate till wanted for use, or prepared fresh as needed. 



Grape Sugar causes Fehling's Solution to form a red precipitate. 



Experiment 7. To show the difference between sugar and 

 STARCH IN regard TO SOLUBILITY. — Mix some sugar with water and 

 notice how readily it dissolves. Try the same experiment with starch 

 and observe its different behavior. 



Experiment 8. To show how starch is disintegrated in the A'^t 

 OF DIGESTION. — Place a few grains of starch on a slide, add a drop or 

 two of diastase solution, and observe under the microscope ; the starch 

 granules will be seen to disintegrate and melt away. Even with a hand 

 lens it can be seen, from the greater clearness of the liquid in comparison 

 with a mixture of untreated starch and water, that the gi-ains have been 

 dissolved. 



