212 VETERINARY HYGIENE 



purpose it is not very suitable, as the extensive application of tar in 

 a stable or byre robs the place of much of its light, which is very 

 seldom over-abundant. The use of tar is, however, quite legitimate 

 in open or temporary stables, cattle courts, and the like. Major 

 J. R. Hodgkins, discussing the disinfection of veterinary stables in 

 France during the War, advocates the use of tar " as a complement 

 to other methods of disinfection." Tar takes a long time to dry, 

 and to get over this difficulty he suggests that, after the usual 

 scrubbing with hot water and antiseptic, the fittings should be 

 subjected to the flame of a brazier's lamp. This dries the iron and 

 woodwork. The tar is then applied and afterwards burned with 

 a lamp and scraped away. The wood becomes creosoted. After 

 several tarrings no more need be applied and all that is required 

 is to boil up the existing tar with the lamp and scrape. 



COAL TAR (Fix Carbonis). This is a black viscid fluid of 

 characteristic and disagreeable odour obtained as a by-product in 

 the manufacture of illuminating gas. Coal tar is a body of very 

 complex composition, and is more or less mixed with ammoniacal 

 liquor as well as with the constituents of illuminating gas itself in 

 solution. It is resolved by fractional distillation into (1) light 

 naphtha; (2) light oil; (3) carbolic oils; (4) creosote oils; (5) 

 anthracene oils; and (6) pitch. 



CARBOLIC ACID (Phenol, C 6 H 5 OH). This popular disinfectant 

 occurs in commerce in various degrees of purity. What is used in 

 surgical practice is almost chemically pure, acidum carbolicum and 

 acidum carbolicum liquefactum, of the British Pharmacopoeia. The 

 latter is made from the former by adding fifteen parts of water to 

 one hundred parts of the pure acid. 



Crude or Commercial Carbolic Acid consists of 95 to 97 per 

 cent, of cresols and higher homologues with but little carbolic acid 

 (phenol). The cresols are at least as valuable disinfectants as 

 pure carbolic acid, and they are the basis of lysol and all similar 

 preparations. There are crude carbolic acids of what is called 25 

 per cent, strength, i.e., they contain 25 per cent, of cresols and the 

 remainder consists of naphthalene oils which are of no value as 

 antiseptics. 



Carbolic acid is obtained from the fraction of coal tar distilling 

 between 150 C and 200 C by agitating with a 20 per cent, solution 

 of caustic soda solution. After standing some time the liquid 

 separates into two layers, the lower one containing phenate or 

 carbolate of soda. This is drawn off, diluted, and exposed to the 

 air, when a brown deposit containing naphthalene is formed. The 

 nitrate is then fractionally precipitated with dilute sulphuric acid, 



