Substitution products of the hydrocarbons. As a rule, at least a part of the hydrogen in any hydrocarbon can be displaced by an equivalent amount of certain elements or groups of elements. Thus the compounds CH3Cl, CH2Cl2, CHCl3, CCl4 can be obtained from methane by treatment with chlorine. Such compounds are called substitution products.
Chloroform (CHCl3). This can be made by treating methane with chlorine, as just indicated, although a much easier method consists in treating alcohol or acetone (which see) with bleaching powder. Chloroform is a heavy liquid having a pleasant odor and a sweetish taste. It is largely used as a solvent and as an anæsthetic in surgery.
Iodoform (CHI3). This is a yellow crystalline solid obtained by treating alcohol with iodine and an alkali. It has a characteristic odor and is used as an antiseptic.
ALCOHOLS
When such a compound as CH3Cl is treated with silver hydroxide the reaction expressed by the following equation takes place:
CH3Cl + AgOH = CH3OH + AgCl.
Similarly C2H5Cl will give C2H5OH and AgCl. The compounds CH3OH and C2H5OH so obtained belong to the class of substances known as alcohols. From their formulas it will be seen that they may be regarded as derived from hydrocarbons by substituting the hydroxyl group (OH) for hydrogen. Thus the alcohol CH3OH may be regarded as derived from methane (CH4) by substituting the group OH for one atom of hydrogen. A great many alcohols are known, and, like the hydrocarbons, they may be grouped into series. The relation between the first three members of the methane series and the corresponding alcohols is shown in the following table:
| CH4 | (methane) | CH3OH | (methyl alcohol). |
| C2H6 | (ethane) | C2H5OH | (ethyl alcohol). |
| C3H8 | (propane) | C3H7OH | (propyl alcohol). |
Methyl alcohol (wood alcohol) (CH3OH). When wood is placed in an air-tight retort and heated, a number of compounds are evolved, the most important of which are the three liquids, methyl alcohol, acetic acid, and acetone. Methyl alcohol is obtained entirely from this source, and on this account is commonly called wood alcohol. It is a colorless liquid which has a density of 0.79 and boils at 67°. It burns with an almost colorless flame and is sometimes used for heating purposes, in place of the more expensive ethyl alcohol. It is a good solvent for organic substances and is used especially as a solvent in the manufacture of varnishes. It is very poisonous.