ALCOHOL (Pr., Alcool ; Ger., Alkohol) Chemically, alcohols are neutral compounds formed by the replacement of hydroxyl OH for one atom of hydrogen in a saturated carbon compound ; for instance, C,H, ethylene gives C,H, OH ethyl hydrate, or ordinary alcohol. They unite with acids with elimination of water to form ethers. Alcohols are hydrates of organic radicles and may be considered as equivalent in organic chemistry to the metallic hydrates in inorganic. For example, KOH potassium hydrate ; OH ethyl hydrate. They are divided into monatomic, diatomic, triatomic, etc., according to the number of OH groups attached to the organic radicle.
Alcohol, Ethyl (Pr., Alcool ordinaire, Alcoa ethylique ; Ger., A ethylalkohol) Synonyms, ethylic alcohol, ethyl hydrate. HO. Molecular weight, 46. Solubilities, miscible with water and ether in all proportions. A colourless, volatile, inflammable liquid of pleasant odour ; it is obtained from grain, starch, or sugar by fermentation and subsequent distillation. It is principally used for preparing collodion (which see).
Absolute Alcohol contains from 98 to 99 per cent. of pure alcohol, and is used for making collodion.
Rectified spirit or spirits of wine contains io per cent, of water, and is known as 58 over proof. The term " proof spirit " refers to an old test with gunpowder, which was moistened with the spirit and then a light applied ; if the gunpowder fired the spirit was termed proof.
Alcohol, Methyl or Methylic (Pr., Alcool methylique ; Ger., Methylalkohol, Holz geist) Synonyms, wood alcohol, wood spirit, wood naphtha, methyl hydrate or hydroxide. CH, OH. Molecular weight, 32. Solubilities, miscible with water, alcohol, and ether in all proportions. A colourless, mobile liquid, prepared by the de structive distillation of wood. It is an excel lent solvent for resins and pyroxylin, with which it gives a very tenacious film.
Alcohol, Methylated (Fr., Alcool denature ; Ger., Brennspiritus) Synonyms, methylated spirit, denatured alcohol or spirit. Solubilities, miscible with water and ether in all proportions. It usually
contains about 90 per cent, of aqueous ethyl alcohol with about io per cent, of methyl alcohol and + of i per cent, of mineral naphtha to render 2 it unpotable. Industrial methylated spirit does not contain naphtha, and can only be obtained by special permit of the Inland Revenue under a heavy bond ; it may be used for nearly all photographic purposes instead of pure alcohol, except for printing-out collodion emulsions. The admixture of methylated spirit with water turns it milky in consequence of the separation of the naphtha.
In process work, alcohol plays an important part. For making up collodion for the wet plate process, absolute alcohol of •805 sp. g. is usually employed. Spirit of wine is used in the wet plate developer to overcome the repellent actions of the silver solution on the plate when the bath has become charged with alcohol through the frequent sensitising of plates. As the bath gets older the proportion of alcohol is increased. Methylated spirit is not generally employed on account of the presence in it of mineral naphtha, which is apt to give fog, scum, and other troubles, but industrial alcohol (wood spirit) may replace the pure spirit on the score of economy. In making up collodion emulsion only pure alcohol should be employed. Alcoholic solutions of dyes are largely used in colour sensitising, and in this case only pure alcohol should be used. Methyl ated spirit is used for drying off the fish-glue print after development. It is also employed for developing resinous images, for making up acid resist varnish, for diluting stopping-out varnish, and for cleaning off varnish coatings. In the aquatint process alcohol is used with resin to give the granular ground which is formed on the plate for etching. Similarly, alcohol is used in certain bitumen processes, such as the Frey process, where the alcohol with the asphalt causes the film to reticulate—that is, to form a network. An alcoholic solution of bichromate is used for sensitising carbon tissue, the object being to promote quicker drying.