Text-Book of Organic Chemistry for Medical Students (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1912 Excerpt: ...with the ordinary solvents, i.e. by boiling with dilute alkalies and acids, alcohol, and ether; what remains behind is moderately pure cellulose, which retains the structure of the original tissue. Linen, cotton wool, and filter-paper are nearly pure cellulose. When these substances are treated first with concentrated sulphuric acid at the ordinary temperature, and then boiled with dilute sulphuric acid, cellulose is broken down into a number of grape-sugar molecules. In the treatment with the concentrated sulphuric acid, cellulose passes into a colloidal modification, which is coloured blue by iodine and is called 'amyloid';1 upon which a reaction for detecting cellulose depends. Technical use is made of this conversion of cellulose into a colloidal substance in the preparation of parchment paper. When ungelatinised paper is acted upon for a short time by concentrated sulphuric acid and is then washed with water, vegetable parchment is obtained; the paper now no longer consists of a felt composed of separate threads of cellulose, nor does it contain pores through which filtration is possible, but it consists of a continuous colloidal mass. Filtration through such parchment paper is not possible, but diffusion is, i.e. when different substances are present in the same solution, all these do not pass through it in proportional quantities, but some pass through more quickly than others. Cellulose dissolves entirely without decomposition in ammoniacal copper oxide solution, from which it is again precipitated by acids and salts as an amorphous powder. When cellulose is treated with a mixture of nitric and sulphuric acids, nitric acid esters are formed, the hydroxyl groups of the cellulose combining with the nitric acid, with elimination of water, in the same w...