SEEDS AND SEEDLINGS. 39 



acid. Introduce a glass rod, on the end of which is a drop of lime- 

 water, into the test-tube. The lime-water becomes milky, showing 

 that carbon dioxide is one of the products of decomposition of starch. 

 This confirms the presence of carbon in starch (since carbon dioxide is 

 a compound of carbon and oxygen). When all the volatile matter has 

 been driven off, a black glistening residue of charcoal remains. 



* (6) Shake a very little starch in a test-tube of cold water and boil well ; 

 add a few drops of iodine solution : a blue colour is formed. Boil the 

 blue solution, and the blue colour disappears, to return on cooling. 



* (c) Boil a little starch with dilute sulphuric acid, and test a few drops 

 of the solution from time to time for (1) starch, and (2) sugar. The re- 

 actions of starch are gradually lost, and those of siigar appear instead. 



* (d) Examine specimens of cane, grape, fruit, and milk sugars. (1) 

 Taste them : they are all sweet. (2) Boil with a solution of caustic 

 potash : cane sugar does not colour the solution, but the others turn 

 it brown. (3) Add a little Rochelle salt (sodium potassium tartrate), 

 then excess of caustic potash, and finally some copper sulphate 

 solution. 1 [The object erf the Rochelle salt is to prevent the precipi- 

 tation of cupric hydroxide by the action of potash on copper sulphate.] 

 Boil : cane sugar only precipitates red cuprous oxide on long boiling, 

 but the others give a precipitate at once. (4) Add a solution of 

 silver nitrate to which excess of ammonia has been added, and warm : 

 the cane sugar only reduces the silver after long boiling ; the others do 

 so very soon. 



(e) Boil some cane sugar with dilute sulphuric acid for ten minutes, 

 and test with Fehling's solution, etc. : it now gives the same reactions 

 as the other sugars. 



These properties of possessing a sweet taste and of turning caustic 

 potash brown and reducing copper sulphate and silver nitrate, either 

 at once or after previous boiling with dilute acids, are characteristic of 

 the sugars. 



67, Froteids, or nitrogenous food-stuffs, composed of 

 carbon, hydrogen, oxygen, nitrogen, sulphur, and in some 

 cases phosphorus, occur in both vegetable and animal tissue, 

 though only plants can build them up from their elements. 

 They form the living substance (protoplasm) found in cells 

 of plants and animals ; in decaying they give off offensive 

 smells. Albumin occurs in white of egg, myosin in lean 

 meat, gluten in flour, casein in milk and cheese, legumin 

 in Peas and Beans. See books on Human Physiology. 



1 This is called Fehling's test. Dissolve 35 grammes of copper 

 sulphate in 200 c.cs. of water to make solution A. To make solution B 

 (to be kept in a separate bottle) dissolve 70 grammes of Rochelle salt 

 in 200 c.cs. of 10 per cent, caustic potash solution. Use equal volumes 

 of solution A, solution B, and water. 



