®^ CHEMISTRY. 



be converted into dextrine and grape sugar by the action of strong 

 sulphuric acid. In its composition it is isomeric with starch. 



SECTION III. 



AZOTIZED VEGETABLE SUBSTANCES. 



These include Gluten, Vegetable albumen, Vegetable fibrin, and 

 Vegetable casein, or Legumen, They are sometimes called vegeto- 

 animal prmciples, from their strong analogy with similar principles 

 found in animals. 



Gluten. — It owes its name to its adhesive property : to it is due 

 the adhesiveness of wheat-dough. It exists chiefly in the seeds of 

 plants, in combination with starch ;— may be separated by washing 

 away the starch from wheat flour. It is almost insoluble in water^ 

 but soluble in alcohol ; gluey when moist, but yellow and translucent 

 when dry. It is a highly nutritious substance. It is owing to it 

 that the rising of wheaten bread is due ; the carbonic acid which is 

 formed by the fermentation of the yeast being entangled in the 

 meshes of the gluten, and thereby imparting the cellular structure to 

 the loaf. 



Vegetable albumen. Vegetable fibrin, and Vegetable casein also 

 exist in vegetables in combination with gluten. Vegetable albumen 

 is coagulated by heat ; vegetable casein is coagulated by acetic acid. 

 The chemical composition of all these principles is nearly, if not 

 quite identical, being C^^HyN^^O,,, with some sulphur. 



SECTION IV. 



OILS AND FATS, 



Oils are divided into two classes, fixed and volatile ; the former 

 produce a greasy stain upon paper, which is permanent under the 

 action of heat; the stain produced by the latter is removed by 

 heat. There is no essential difference between oils and fats; the 

 chief distinction is in their different degrees of consistency. All of 

 them have more or less attraction for oxygen; some of them to such 

 an extent as to produce spontaneous combustion of light substances 

 moistened with them. This is very apt to be the case with linseed 

 oil; from this results the division of fixed oils into drying and non- 

 drying : the oils used in painting belong to the first class. 



The parts of vegetables which contain most oils are the seeds; 

 olive oil is obtained from the fruit itself. 



The fixed oils have but slight odour or taste ; whenever these qua- 

 hties are found in a fixed oil, they are due to a volatile principle 

 associated with it, as in the case of butter. They are all insoluble 



