DISINFECTANTS, ETC. 143 



exceptions. When these differences were all divided by 3, 

 the series of numbers were in many cases identical with, 

 or very close to, the carbolic acid co-efficient independently 

 arrived at for each substance. In the cases where there 

 was a divergence, the disinfectant did not form an emulsion 

 with water, and the solution did not exhibit Brownian 

 movements. Thus, it was deduced that the formula 

 (P - B) -h 3 gives the carbolic acid co-efficient for B. coli 

 of the disinfectant tested, where P is the percentage of 

 phenoloids present, B the carbolic acid equivalent of 

 these (calculated), and 3 an arbitrary constant. 



From a chemico-physical point of view, it is concluded 

 that for tar disinfectants, at any rate, they should contain 

 a reasonable quantity of active bodies, phenols or 

 phenoloids, and that the dilution of them in water should 

 show active Brownian movements, that is, should form a 

 satisfactory emulsion. The formula (P B) -4-3 gives a 

 ready means of estimating the carbolic co-efficient of a 

 disinfectant, and its value should be at least over unity, 

 that is, be equal to pure carbolic acid. A number of the 

 disinfectants at present in common use give values of 

 5 to 9 by this method. 



