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. (Fehling's solution is made by taking one part each of these three solutions and two parts of water: (1) 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 example 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 proteid (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.
