PRELIMINARY EXPERIMENTS XV 



tion treated in like manner may be examined under the 

 microscope, and the fine particles, precipitated from the 

 sugar of the pear, may be clearly seen. {Fehlings solution 

 is made by taking one part each of these three solutions 

 and two parts of water: (i) Copper sulfate, 9 grams in 

 250 cubic centimeters of water; (2) sodium hydroxid, 30 

 grams in 250 c.c. water; (3) Rochelle salts, 43 grams in 

 250 c.c. water.) 



Test for Nitrogenous Substances, or Proteids. — Put a little 

 white of egg into a test tube and heat slowly. What change 

 takes place in the egg ? Put another part of the white of 

 egg into a test tube and add dilute nitric acid. Compare 

 the results of the two experiments. White of egg is an ex- 

 ample of a proteid ; that is, it is the form of nitrogen most 

 commonly found in plant and animal tissue, and it can be 

 formed only by life processes. Do acid and heat harden 

 or soften most substances ? Either of the above tests 

 reveal proteid, if present. Does cooking tend to soften or 

 toughen lean meat ? 



Another test for proteid is nitric acid, which turns pro- 

 teid (and hardly anything else) yellow. Proteid when 

 burned has a characteristic odor ; this will be noticed if lean 

 meat or cheese is charred in a spoon. The offensive odor 

 from decomposing proteid is also characteristic, whether 

 it comes from stale beans, meat, mushrooms, or other 

 things containing proteid. 



Test for Fats and Oils. — Place a little tallow from a 

 candle on unglazed paper and warm. Hold the paper up 

 to the light and examine it. What effect has the fat had on 

 the paper ? Place a little starch, sugar, powdered chalk, or 

 white of egg on paper and repeat the experiment ; is the 

 effect the same ? Place some of the tallow in a spoon, and 

 heat. Compare the effect of heat on fat and proteid. 



