CHEMISTRY. 181 



have great similarity, and only within the last few months have 

 they been met with separately in commerce, having hitherto been 

 both called "carbolic acid. Creosote, prepared from coal tar, was 

 thought to be impure carbolic "acid, until 1854, when Professor 

 Williamson and Mr. Fairlie, in an investigation of it, discovered 

 that it w r as a mixture of carbolic and cresylic acids. It was then 

 taken for granted that Reichenbach's creosote, from wood tar, had 

 a similar composition, until Hlasiwetz, in 1858, showed that this 

 creosote was a different body from carbolic or cresylic acids. 

 Finally, Dr. Hugo Miller, in 1866, discovered that true creosote 

 and its analogue guaiacol belonged to a different class of bodies, 

 and consisted of methyl-oxy-pkenic and rnethyl-oxy-cresylic 

 acids. 



" Pure carbolic acid is a white crystalline solid, melting at 34 

 C., and distilled at 180 C. ; a trace of water or oily impurity ren- 

 ders it liquid, and for disinfecting purposes it is always supplied in 

 this form, to avoid the extra expense and trouble needed for the 

 separation of the last traces of impurity. Cresylic acid is liquid, 

 boils at 203 C., and closely resembles carbolic acid in odor and 

 other properties. Before the commencement of these inquiries, it 

 was thought to be of little or no value as a disinfectant, but Dr. 

 Angus .Smith has lately shown that it rivals, if it does not surpass, 

 carbolic acid in antiseptic properties. For the present purpose of 

 cattle plague disinfection, it is immaterial which acid is. used, and, 

 to avoid unnecessary repetition, I shall use the term carbolic acid 

 to express either acid, or the commercial mixture of the two 

 acids. 



" From time immemorial carbolic acid, creosote, or bodies con- 

 taining them, have been used as antiseptics. Carbolic acid is the 

 active agent in tar, which, either in its ordinary state, or burnt as 

 a fumigator, has always held high rank among disinfectants. 

 Pitch and tar were the most popular medicines in use against the 

 cattle plague when it visited this island in the last century; the 

 animals being preserved against contagion by having their noses 

 and jaws rubbed with tar, whilst the cow-houses were disinfected 

 by burning pitch and tar in them (in which process a certain quan- 

 tity of the vapors of carbolic acid would escape combustion). 

 The well-known efficacy of smoke in preserving meat is entirely 

 due to the presence in it of this agent. 



"Pitch oil, oil of tar, and similar products, owe their value en- 

 tirely to carbolic acid. This body may in fact be called the active 

 principle of tar, just as quinia is the active principle of bark, or 

 morphia of opium, and it has the advantage of being easily pre- 

 pared in any country where coal or wood can be obtained. 



" Sulphurous acid probably owes some of its antiseptic value to 

 its affinity for oxygen, whereby the oxidation of the matter under 

 treatment is retarded. It has been suggested that the value of 

 carbolic acid is due to a similar property, and that it acts merely 

 by preventing oxidation. It being important to a thorough under- 

 standing of its action that this point should be settled, the follow- 

 ing experiments were made : 



' I. Lumps of metallic sodium were cut with a sharp knife ; the 



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