40 • INTRODUCTION. 



place, and there is a formation of volatile oil of bitter almonds, hydrocyanic 

 acid, &c. 



Compounds not containing Nitrogen. 



Many of these compounds have their oxygen and hydrogen in the same 

 proportions as those of water, and most of them can be converted into sugar 

 when boiled a long time with an acid or alkali. In others of them, their hy- 

 drogen or oxygen is in much greater proportion than in water. 



Oxygen and. Hydrogen in same proportions as Water. 



Lignin. Is a fibrous substance, destitute of taste or smell, and when per- 

 fectly dry, not alterable by the action of the air, but when moist, becoming 

 decomposed, furnishing carbonic acid and water. When boiled with sulphu- 

 ric acid, it is changed into dextrine, and afterwards into sugar. It constitutes 

 about l-100th of dried wood. Comp. C 12 H 10 O 10 . 



Starch. Is contained in vegetable cells, in the form of granules, covered 

 with an envelope not soluble in cold water. The granules vary much in 

 size and appearance in different plants. It is changed by heat into dextrine, 

 a soluble starch having the same composition ; by boiling with dilute sulphu- 

 ric acid, it is converted into sugar. It is coloured blue by free iodine, which 

 is the best test for it. Comp. O 2 H 10 O 10 . 



Many kinds of starch are employed as dietetic articles, under the names of 

 sago, tapioca, arrow-root, &c. ; these, though possessing the same general pro- 

 perties, differ much in flavour, and in the form and appearance of their granules. 

 Wheat Starch, when pure, is white, and almost tasteless, and without 

 odour. Under the microscope, it appears to con- 

 F) g- 38 - sist of particles varying much in size, of which the 



largest and smallest are the most frequent, the 

 intermediate ones being scarcer. Their shape 

 is usually rounded, and their surface uneven. 

 The hilum is surrounded by concentric rings, 

 but is by no means evident, until a gentle heat is 

 applied to the water in which the particles are sus- 

 pended. Sometimes it is indicated by a line or 

 a a particL^seen edgeways. rounded spot ; the rings are traceable to the edge 

 of the granule. When made to roll over in the 

 fluid, they appear like oblate spheroids, one of the faces being rather more 

 convex than the other. 



Arrow-Root, West Indian, is white, without taste or smell. When 



pressed between the fingers, it feels firm, and on 



Fl s-%>- being rubbed, produces a faint, crackling sound. 



fj^^B *^ Under the microscope it appears to consist of oblong, 



gk r\MKk or ovate-oblong, or irregularly-shaped granules, hav- 



E^ i ] ^T|)| ing, occasionally, small mammillary points projecting 



^^r A^^ fiy from the surface, which are more evident after the 



^i^ wr particles have been in water for a short time. The 



/*■* rings arc very delicate, and the hilum is circular, and 



oot. j jas ]j near or stellate cracks. Procured from Maran- 



ta arandinacea. 



