io6 PLANT PRODUCTS 



or sulphuric acid. Solutions of cellulose in cuprammonium 

 hydroxide are used in making Willesden paper and canvas ; 

 solutions in zinc chloride are used for electric carbon fila- 

 ments ; and solutions in sulphuric acid are used for parch- 

 ment paper. Many of the fibrous parts of plants are not 

 pure, but contain furfuroids, lignin, etc. 



Starch, (CeHjQOg), or probably slightly more hydrated, 

 is a very common form of storing reserves of plant foods in 

 seeds, stems, bulbs, and other parts of a plant where they 

 are not required at the time, but at some later stage of the 

 plant growth. Starch is commonly recognized by its 

 microscopic form and reaction with iodine. A microscope 

 with Nicol prisms is of great use in observing starch grains. 

 Dry heat above 150° Cent, converts starch into dextrin. 

 In the presence of water, starch grains burst when heated. 

 Starch is soluble in hot water, forming a colloidal solution. 

 Potato starch gelatinizes at 65°, but oat starch needs 95° 

 Cent. On the addition of a drop of copper sulphate to a 

 solution of starch, followed by a large excess of sodium 

 hydroxide, a blue precipitate is produced, which is not 

 altered on boiling. The action of ferments, such as diastase, 

 turns starch into soluble products, dextrin, malto-dextrin, 

 maltose, etc. Further treatment with dilute acid will 

 convert these products into glucose (dextrose). Diastase 

 is a typical enzyme, and has the power of converting 1000 

 times its own weight of starch into soluble materials. 



Dextrin, a body very similar to starch, is generally 

 present in plants to a small extent, and can be obtained by 

 heating starch either by itself or in presence of water or 

 with traces of nitric acid. It differs from starch in giving 

 a red colour with iodine. Dextrin is used in place of gum, 

 especially in hot climates, as it is less hygroscopic than gum 

 arabic. For small articles, like postage stamps, dextrin 

 is superior to gum arabic, but for large articles its adhesive 

 power is too small. 



The Mono-Saccharoses, or Hexoses, C6H12O6. — 

 Glucose (dextrose, grape sugar) occurs in all the sweet-tasting 

 plants, crystallizes with some difficulty, often with one molecule 



