TESTS FOR SUGABS AND OIL 241 



nectar of flowers it attracts insects. To test for glucost : 

 Make a thick section of a bil of the edible part of a 

 pear and place it in a bath of Fehliug's solution. After 

 a few moments l>oil the Liquid containing the section for 

 one or two minutes. It will turn to an orange color, 

 showing a deposit of an oxide of copper and perhaps 

 a little copper in the metallic form. A thin section 

 treated in like manner may be examined under the micro- 

 scope, and the fine particles, precipitated from the solution 

 by the sugar of the pear, may be clearly seen. (Fehling's 

 solution is made by taking one part each of these three 

 solutions ami two parts of water: (1) Copper sulfate 

 grams in 250 >-.<. water; (2) sodium hydroxide, 30 grams 

 in 250 c.c. water; (:;) pochelle -alt-. 43 grams in 250 c.c. 

 water.) To test for earn sugar: (1) .Make a thin section 

 of sugar heet ami let it stand a few minutes in a strong 

 solution of copper sulfate. Then carefully rinse off all 

 the salt. (_) Heat in a very strong solution of potassium 

 hydroxide. There will be seen a blue coloration in the 

 section, gradually washing oul into the liquid. 



To test for oil: Mount a thin Bection of the endosperm 

 of castor-oil seed in water ami examine with high power. 

 Small drops "f oil will he quite abundunt. Treat the 

 mount with alcanin (henna pool in alcohol). The drops 

 of oil will -tain red. This is the standard test for fata 



and oils. 



To examitn gum resin: Mount a little of the "milky" 

 juice of the leaf stem of the garden poinsettia (Euphorbia 

 pulcherrima) . It is "f a cream} consistency. Examina- 

 tion under the microscope -how- that it I- not white, a- 



it seems to the naked eye. The particles are yellowish 

 or colorless ami an- insoluble. These particle- are gum 

 resin. Thej have been emulsified bj the plant, making 



t he juice appear while. 



398. CONTENTS NOT IN SOLUTION St.uch ; the -t 



