Define isomerism. ISOMERISM. Two compounds are said to be isomeric when they have the same percentage-composition, but show different properties. They are divided into two classes: (a) those that have the same molecular weight are called metameric; (b) those that have a different molecular weight are called polymeric. What are metameric bodies? (a) Bodies which have the same percentage-composition and molecular weight, but show different decompositions under similar conditions, are called metameric. Thus three bodies correspond to the formula C,H,O: (b) Bodies which have the same percentage-composition, but different molecular weights, are called polymeric. Thus :: CLASSES OF ORGANIC COMPOUNDS. Give a classification of organic compounds, with the name and graphic formula of each. HYDROCARBONS. The various compounds of carbon and hydrogen are called hydrocarbons. They are all derived from methane or marsh-gas, CH1. One series is formed by replacing a hydrogen atom in CH, by (CH), called methyl, thus giving CH-CH,, ethane; and so on, CH-CH2-CH,, propane, etc. If two hydrogens are replaced by (CH2)", an unsaturated series of compounds is formed, called olefines: (CH=CH,), ethylene, If three are replaced by the radical (CH)''', then acetylenes are formed: CH=CH, acetylene. The other unsaturated hydrocarbons are given below. Give the different series of hydrocarbons. Methane or marsh-gas (CnH2n+2) Ethane CH C3H8 gases. CH2 liquid. C35H729 solid. Ethylene, C2H.; Propylene, C,H; Butylene, C¡Í ̧, etc. The next are acetylenes, CnH2n — 2 :— 8, Acetylene, C2H2; Allylene, C,H.; Crotonylene, C,H Mention some other unsaturated hydrocarbons. Dipropargyl, (CnH2n-6)CH; this compound is isomeric with the aromatic compound benzene, C.H.. What are meant by primary, secondary, and tertiary compounds? When two radicals are joined to the radical (CH2)" the compound is said to have a primary structure; if three radicals are joined to (CH)", it is called secondary, and if all the hydrogens in methane, or (CH,), are replaced by radicals, the compound is called tertiary :— These names are not only applied to "hydrocarbons," but also to other derivatives, as alcohols : CH2 CH CH3-CH2-CH,—OH—, CH2 CH-OH, CH-C-OH. Primary alcohol. Secondary alcohol. Tertiary alcohol. THE HYDROCARBONS IN DETAIL. Give the occurrence and formation of the paraffines CnH2n+2. Many of the paraffines occur ready formed in American petroleum and other mineral oils of similar origin, namely: Natural gas, coal oil, asphalt oil, and other natural residues of decomposition of vegetation like boghead, cannel coal, and Burmese tar. Describe the method of purifying petroleum. It is first treated with concentrated sulphuric acid, which dissolves the unsaturated hydrocarbons and destroys other organic substances. The acid is then drawn off (called sludge acid or "sludge') and the oil treated with caustic soda, washed, and distilled. Give the products and the average yield of a sample of petroleum. Paraffines are also formed by the action of zinc and water on the haloid ethers : 2C2H ̧I+2Zn+2H2O = 2C2H ̧+Zn(OH)2+ZnI2. What are the properties of paraffines? The paraffines, depending on their carbon-contents, are either solids, liquids, or gases. They are saturated hydrocarbons, i. e., cannot form additional products. Chlorine and bromine in sunlight give substitution-products. They are not easily acted upon by reagents. The lower members are not attacked by nitric acid, but the higher ones form nitro compounds. What are cyanides or nitryls? They are paraffines in which one or more hydrogen atoms have been replaced by cyanogen, CN or Cy: C2H,CN from C2H. The most important member of this group is hydrogen cyanide, or |