140 PUBLIC HEALTH CHEMISTRY 



is published in the " Lancet " for 1909, Vol. ii., pages 1454 

 (Chemical), 1516 (Bacteriological), and 1612 (Summary and 

 Conclusions) . 



The chemical part is here dealt with. Disinfectant is 

 taken to mean a substance capable of destroying disease 

 germs, or a " germicide," which is a preferable word. 



CHEMICAL ANALYSIS. 



Arguing that disinfection is a chemical process, the 

 standards laid down are these : 



1. A standardized disinfectant should contain a certain 

 proportion of an accredited germicidal substance ; and 



2. If it is presented as a soapy mixture, which makes 

 an emulsion with water, such dilution in water should 

 show active Brownian movements of the particles 

 distributed in the mixture. 



The coal-tar disinfectants form the majority of those 

 sold to the public. They consist of varying quantities of 

 phenolic bodies, with inert tar oils, and in many cases 

 soap and resins or other emulsifying agents, such as gelatin 

 or dextrin, etc. The analysis of these mixtures necessitates 

 the separation of the soap, resin, or oily hydrocarbons 

 present, before the presence of phenol, cresol, or other 

 phenoloid body can be properly tested for. The existing 

 methods were found to be inconvenient, tedious, and 

 troublesome, and the following method was devised and 

 worked out by testing a large series of these mixtures. 

 Distillation methods were avoided, because of the relatively 

 large quantity of disinfectant required, and the incon- 

 venience of the operations in any but a technical 

 laboratory, while solvent processes were objected to, on 

 account of the difficulty in separating the solvent, and 

 also because no differentiation of the kind of phenol 

 present was attempted. 



The Lancet-Acetone-Baryta (L.A.B.) Method. 



i. For fluids containing soaps and resins as emulsifiers. 

 The process consists in making an emulsion with a known 

 weight of the disinfectant mixed with water ; precipitating 

 the soaps and (or) resins by adding a strong solution of 



