Theoretical organic chemistry / by Julius B. Cohen.

  • Cohen, Julius B. (Julius Berend), 1859-1935.
Date:
1942
Catalogue details

Licence: In copyright

Credit: Theoretical organic chemistry / by Julius B. Cohen. Source: Wellcome Collection.

    38/636 (page 18)
    course be examined in this way; but the gases or liquids may be burnt in a closed vessel, or the vapour led over a layer of red-hot copper oxide and then through lime-water. Nitrogen.—When nitrogenous organic compounds are heated with metallic potassium or sodium, potassium or sodium cyanide is formed, and the subsequent test is the same as for a cyanide (p. 216). Expt. 4.—Pour about 10 c.c. of distilled water into a small beaker. Place a fragment of gelatine or cheese in a small test-tube along with a piece of metallic potassium or sodium the size of a coffee bean, and heat them, at first gently, until the reaction subsides, and then strongly, until the glass is nearly red-hot. Place the hot end of the tube in the small beaker of water. The glass crumbles away, and any residual alkali metal is decomposed with a bright flash; all the cyanide rapidly goes into solution, whilst a small quantity of carbon remains suspended in the liquid. Filter through a small filter into a test-tube. Pour into the clear solution about 1 c.c. of ferrous sulphate solution, to which a drop of ferric chloride has been added, boil for a minute, cool, and acidify with dilute hydrochloric acid. A precipitate of Prussian blue indicates the presence of nitrogen. In many cases nitrogen may be detected by heating the substance with soda-lime, when the nitrogen is evolved as ammonia. Expt. 5.—Grind up a small fragment of cheese with about four times its bulk of soda-lime; introduce the mixture into a test-tube, and cover it with a shallow layer of soda-lime. Heat the test-tube strongly, and at the same time hold a piece of moistened red litmus at the mouth of the tube. If it is turned blue, nitrogen is present. Halogens.—Many halogen compounds impart a green fringe to the outer mantle of the non-luminous flame. A more delicate test is to heat the substance with copper oxide, which gives a vivid green coloration. Expt. 6.—Heat a fragment of copper oxide, held in the loop of a platinum wire, in the outer mantle of the non-luminous flame, until it ceases to colour the flame green. Let it cool down a little, and then dust on some halogen compound. Now heat again. A bright green flame, accompanied by a blue zone immediately round the oxide, indicates the presence of a halogen. The halogen in the majority of organic compounds is not directly precipitated by silver nitrate. This may be seen by adding silver