462 APPLIED BIOLOGY 



Or lay a piece of suet on a paper and heat slowly. This "grease- 

 spot" test is a simple way of finding whether fats or oils are present 

 in foods. 



Tests for Protein. (D or L) Mix a small quantity of white-of-egg 

 in water in a test-tube, shake well, add some strong nitric acid, 

 boil until the solution turns yellow, then add drops of ammonia 

 until an orange color appears. Or instead of the acid, add to the 

 egg-albumen in water some drops of Millon's reagent (mercury 

 dissolved in nitric acid ; obtainable from chemists), heat slowly, and 

 red color will appear, especially after cooling. 



Tests for Water and Minerals. The loss of weight by drying foods 

 is chiefly due to evaporation of water. The ashes left after burning 

 foods represent the mineral contents. By complicated processes 

 chemists can analyze the ashes and determine the kind and propor- 

 tion of elements present. 



378. Sugars and Starches : Carbohydrates. All sugars 

 and starches are grouped together under the name of car- 

 bohydrates. They contain but three elements : carbon, 

 hydrogen, and oxygen. We have already learned that starch 

 is formed in plant cells which have chlorophyll, and that 

 starch is readily digested by enzymes into sugar, or sugar 

 turned back again to starch for storage. The carbohydrates 

 which are used as human foods are chiefly cane-sugar or 

 sucrose and milk-sugar or lactose (both with the formula 

 Ci2H 2 20n) ; grape-sugar and fruit-sugar (both with the 

 formula CeHiaOe) ; and starch (formula is some multiple of 

 C 6 H 10 5 ). 



As we have seen, grape-sugar is found in raisins and other 

 fruits. Under the names of glucose and corn-syrup it is com- 

 mon in the markets, and is made by treating the starch of 

 corn grains with strong sulphuric acid. Lactose or milk- 

 sugar is sold in all drug-stores for use in preparing foods for 

 infants and invalids. Malt- or barley-sugar (maltose) is 

 also sold, especially for flavoring candies, etc. The common 

 " granulated " sugars in our markets are sucrose from the 

 juices of sugar-cane and sugar-beet. The yellow and brown 

 sugars are the crude sugars obtained by evaporating the juice 



