40 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



same time there is probably no disinfectant that is so uncertain in 

 its effect if used without a proper understanding of its nature. The 

 commercial crude carbolic acid is one of the products of coal-tar 

 distillation, and consists essentially of a mixture of coal-tar oils and 

 so-called "cresylic acid" with little or no phenol. The oils are prac- 

 tically inert as disinfectants, but the cresylic acid, which is a mix- 

 ture of cresols and similar homologues of carbolic acid, has very 

 marked disinfecting power. 



As crude carbolic acid depends almost exclusively upon the 

 cresylic acid which it contains for its disinfecting power, it should 

 not be employed unless the cresylic acid content is definitely known. 

 Even then it must be regarded as of doubtful efficiency if the per- 

 centage of hydrocarbon oils is relatively very large, for the oil will 

 prevent to a great extent the solution of the cresylic acid in water 

 when this is mixed with the crude carbolic acid for use as a disin- 

 fectant. As is stated in the paragraph dealing with cresol, the cre- 

 sylic acid is used in 2 per cent solution in water as a disinfectant. 

 When crude carbolic acid is employed, the amount of acid which it 

 contains should be known and the disinfecting solution should be 

 made of such strength that it will contain 2 per cent of cresylic acid. 

 This disinfecting solution or mixture is best applied by means of a 

 spray pump, and while spraying the mixture should be well agitated 

 in order that the oils containing undissolved cresols may be evenly 

 distributed over the surface to be disinfected. 



There are found on the market products which are sold as 

 liquid carbolic acid, straw-colored carbolic acid, etc. ; these, as a rule, 

 contain from 90 to 98 per cent of cresylic acid and very little coal- 

 tar oil. They are considered in the next section dealing with cresols. 



CRESOL. 



Cresol (tricresol, straw-colored carbolic acid, liquid carbolic 

 acid), is derived from coal tar and is found in the trade in varying 

 degrees of purity. The cresol of the United States Pharmacopoeia 

 is a colorless liquid, having a strong odor resembling that of carbolic 

 acid. It consists of a mixture of three closely related bodies, all of 

 which are superior to carbolic acid as disinfectants. The other 

 grades of cresol usually contain a small percentage of impurities, 

 and are sold as liquid carbolic acid, 95 per cent, straw-colored car- 

 bolic acid, etc. These usually contain from 90 to 98 per cent of 

 cresol, and may be purchased under a guaranty to contain certain 

 definite amounts of cresylic acid. Grades containing less than 90 

 per cent of cresylic acid are not so desirable as those of a higher 

 degree of purity, as the coal-tar oils which are usually found in such 

 products interfere with the solution of the cresols in water, as al- 

 ready stated. 



The commercial cresols guaranteed to contain more than 90 

 per cent of cresylio acid are relatively cheap and well suited to the 

 disinfection of cars,, barns, and yards. For general disinfection a 

 1 l /2 to 2 per cent solution of cresol in water should be used, allow- 

 ance being made for the impurities when the cheaper grades are 

 employed. Cresol is not easily soluble in water; therefore, in pre- 



