46 STUDIES IN PHYSIOLOGY 



whole is boiled. If grape sugar is present, the blue Feh- 

 ling's solution will be changed to a yellow, a deep orange, or 

 a brick-red color ; if it is not present, none of these colors 

 will be formed. 



Test for Mineral Matters. 1 The test for mineral matters 

 has been already suggested in connection with the match 

 experiments. If, when foods are burned, ashes are left 

 behind, we may conclude that mineral matters are among 

 the ingredients of the foods we are testing. 



Test for Water. 2 The water, found in varying quantities 

 in all foods, may be obtained by putting the food into a 

 closed dish, from which passes out a delivery tube like 

 that used in the distillation of alcohol. When the dish 

 is heated, the water is driven off as vapor. This is cooled 

 as it passes through the delivery tube, and falls in drops. 

 The percentage of water may be determined, as in the 

 case of the round beef, by weighing the food before and 

 after drying. 



Pure Food Laws. One of the most important laws passed 

 by the 59th Congress of the United States was that which 

 compels every manufacturer of foods or medicines to state 

 on the label the composition of each. Analysis of foods 

 and drugs have proven that hitherto many of them were 

 largely adulterated by cheap and often injurious compounds, 

 put in to increase the manufacturers' profits. Then, too, as 

 already stated, many patent medicines contain high per- 

 centages of alcohol and other dangerous drugs. Under the 

 new law the purchaser, if he takes the trouble to read the 



quantities from the tablets that can be obtained from druggists, or 

 from John Wyeth & Brothers, Chemists, Philadelphia. Before making 

 any tests, boil a small quantity of the Fehling's solution in a clean 

 test tube. If it retains its transparent blue color, it is ready for use ; 

 otherwise a fresh supply must be prepared. From "Laboratory 

 Exercises." Henry Holt & Co. 



1 See "Laboratory Exercises," No. 13. 



2 See "Laboratory Exercises," No. 8. 



