CREOSOTE or 'CREOSOTE. In 1832 Reichenbach applied the term "kreosote" to a substance possessing powerful antisep tic properties and derived from wood tar. Shortly afterwards, Runge discovered carbolic acid in coal tar and showed that it possessed many of the characteristics of "kreosote." The isola tion of similar products from various sources, however, has led to the adoption of the term "creosote" as signifying the mixture of phenol and phenoloid substances derived indifferently from coal, wood, blast furnace, and other tars and from shale and bone oils. In pharmaceutical circles, however, the term "creosote" is still restricted to the product isolated from wood tar, but in industry it is loosely applied to designate that fraction of oils distilling at 200°-300° C. and derived from coal tar. Owing to their dis tinctive character, the creosotes from wood tar and from blast furnace tar are known as "wood-tar creosote" and "blast-furnace creosote." Wood-tar Creosote.—By the distillation of wood tar, particu larly of that derived from the carbonization of beechwood, a fraction heavier than water is obtained, from which, of ter redis tillation to remove last traces of acetic acid, a complex mixture of phenolic substances can be isolated by a treatment similar to that described for the extraction of phenol from coal tar. (See CARBOLIC ACID.) Wood-tar creosote, a colourless, transparent, highly refractive oil of specific gravity 1.037 to 1.087 distils between 205° and 225°C and burns with a very smoky flame. It dissolves in 200 parts of water. A powerful antiseptic, it is non-poisonous and much less caustic than carbolic acid. It dissolves sulphur, resins and phosphorus. It is composed of monohydric phenols and the methyl ethers of di- and tri-hydric phenols. Phenol, the cresols and xylenols occur in small quantities, but the major constituents are guaiacol and methylguaiacol. Small amounts of dimethyl pyrogallol, the dimethyl ether of methylpyrogallol and other ethers are also present. Propylguaiacol, or coerulignol, is often present in the crude product. This substance possesses such astringent properties that a single drop placed on the tongue causes bleeding. Purified creosote, especially for medicinal pur poses, should be free from this compound which may be detected by the blue coloration produced by barium hydroxide. The pro portions in which these constituents occur vary with the con ditions under which the wood is carbonized. (See TARS, Low TEMPERATURE.) .
The distinctive properties of wood-tar creosote are due to the guaiacols. It is insoluble in absolute glycerol and is thus sharply distinguished from coal-tar acids which are completely soluble. It dissolves completely in an ethereal solution of collodion, whereas carbolic acid gives an immediate precipitate.
Purified wood-tar creosote is extensively used for pharma ceutical purposes. Beechwood creosote alone should be used in medicine, as its composition renders it much more valuable than other creosotes. Its constituents circulate unchanged in the blood and are excreted by the lungs. Carbolic acid has no value in the treatment of phthisis (pulmonary tuberculosis) or any other bac terial affection of the lungs; but creosote, being powerfully anti septic and non-poisonous, is very valuable in this direction. It is administered either suspended in mucilage or in capsules. Like carbolic acid, wood-tar creosote, owing to its local antiseptic and anaesthetic action, is of ten useful in relieving gastric pain due to ulcer or cancer and in afflictions due to gastric irritation. When inhaled it brings considerable relief to sufferers from bronchitis, bronchopneumonia, lobar pneumonia and other bacterial lung diseases.
In many applications creosote has been replaced by creosotal (creosote carbonate), a mixture of the carbonates of the phenols present in creosote and prepared by the action of phosgene gas on a solution of beechwood creosote in caustic soda solution. It is a viscous, yellow liquid, insoluble in water but soluble in organic solvents. It is odourless, tasteless and non-irritant in its action on mucous membrane and is therefore used in bronchial affections, phthisis and pneumonia, particularly in children. Other salts of creosote used in medicine are the phosphate (phosphote), phos phite (phosphotal) and valerianate (eosote).
Wood-tar creosote is also used as a source of pure guaiacol, the residue being used as a preservative for wood.
Coal-tar Creosote consists mainly of a mixture of liquid hydrocarbon oils with naphthalene obtained in the distillation of coal tar. The content of naphthalene varies, in some cases being so small that the oils are able to hold it all in solution, whilst in others it is so high that the oils are solid at ordinary tempera tures. Phenolic compounds (tar acids), to which the fraction owes its disinfectant and preservative qualities, are present to the extent of 8 to r o% ; but a creosote much richer in phenols can be obtained by a partial distillation which removes the naphthalene, leaving a residue in which the phenolic content is as high as 3o%. The creosote fraction is often mixed with the anthracene oils, owing to the circumstance that the demand for anthracene has practically vanished and that the isolation and purification of this hydrocarbon has become unremunerative and is rendered more difficult by the introduction of vertical-retort tar, which contains paraffinoid substances. The addition of the anthracene oil to the creosote is not altogether a disadvantage, since the specifications for creosote for the preservation of timber demand a certain percentage of high oils. Unfortunately, the creosote storage tank in many places is becoming the refuse pit for all manner of non marketable oils and tars, such as blast-furnace tar, water-gas tar, etc. It is, therefore, somewhat difficult to assign a definite composition to coal-tar creosote ; but a good sample should have a specific gravity of r •o3 to 1 .08, be quite clear at r 5 ° C and distil between 200° and 300° C. The phenolic content should be in the region of ro%. For the uses of coal-tar creosote see COAL TAR.
Other Creosotes.—The oils derived from low-temperature coal tar and corresponding in boiling point with coal-tar creosote are characterized by the presence of paraffins, the complete absence of naphthalene, a specific gravity less than unity and a high con tent of tar acids containing a very small. amount of phenol. Vertical-retort tar, particularly if steam has been employed in the carbonization of the coal, yields a creosote fraction resembling that from low-temperature tar in many respects, although it usu ally contains naphthalene. Creosote from producer-gas tar con tains large quantities of high-boiling tar acids and paraffins, whilst that from water-gas tar is characterized by the absence of tar acids, richness in paraffins and low specific gravity.
Blast-furnace creosote, sometimes known also as "phenoloid," resembles vertical-retort tar and low-temperature tar creosotes in its content of paraffins and tar acids and its specific gravity. It is noteworthy, however, for the presence of guaiacol and methyl guaiacol amongst the phenols, which amount to 20 to 35% of the fraction. From this creosote a new antiseptic called "neosote" has been prepared. It is less caustic than carbolic acid, and when freshly prepared is almost colourless and bears a close resemblance to wood-tar creosote.