I3 6 THE VITAL PROCESSES 



which has been thoroughly dried (dried beef .or the lean of hard cured 

 bacon). Heat strongly in the hood of a chemical laboratory or some 

 other place where the odors do not get into the room. First hold in 

 the escaping gases a wet strip of red litmus paper. This will be turned 

 blue, showing ammonia (NH 3 ) to be escaping. Next hold in the 

 mouth of the tube a strip of a paper wet with a solution of lead nitrate. 

 This is turned black or brown on account of hydrogen sulphide (H 2 S) 

 which is being driven off. Observe also that water condenses in the 

 upper part of the tube and that a black, charred mass remains behind. 

 Since the products of decomposition (H,O, NH 3 , H^S, and the charred 

 mass) contain hydrogen, oxygen, nitrogen, sulphur, and carbon, these 

 elements are of course present in the proteid tested. 



To show the Presence of Mineral Matter. Burn a piece of dry 

 bread by holding it in a clear, hot flame, and observe the ash that is 

 left behind. This is the mineral matter present in the bread. 



Tests for Nutrients. Proteids. Cover the substance to be tested 

 with strong, nitric acid and heat gradually to boiling. If proteid is pres- 

 ent it turns yellow and partly dissolves in the acid, forming a yellow 

 solution. Let cool and then add ammonia. The yellow solid and the 

 solution are turned a deep orange color. Apply this test to foods con- 

 taining proteid such as white of egg, cheese, lean meat, etc. 



Starch. (a) Place a small lump of starch in one fourth of a pint of 

 water and heat gradually to boiling, stirring well. Then add enough 

 water to form a thin liquid and fill a test tube half full. Add to this 

 a few drops of a solution of iodine. (Prepare by dissolving a crystal 

 of iodine in 25 cubic centimeters (^ pint) of a solution of potassium 

 iodide in water and add water to this until it is a light amber color.) 

 The starch solution is turned blue, (b) Cut with a razor a thin slice 

 from a potato. Place this in a weak solution of iodine for a few 

 minutes' and then examine with the microscope, using first a low and 

 then a high power. Numerous starch grains inclosed in cellulose walls 

 will be seen (Fig. 60). 



Dextrose, or Grape Sugar. Place a solution of the substance sup- 

 posed to contain grape sugar in a test tube and add a few drops of a 

 dilute solution of copper sulphate. Then add sodium hydroxide solu- 

 tion until the precipitate which first forms is redissolved and a clear blue 

 liquid obtained. Heat the upper portion of the liquid slowly to near 

 the boiling point. A little below the boiling point the blue color dis- 

 appears and a yellow-red precipitate is formed. If the upper layer of 



