Comparative Power of some Disinfectants. 97 



days, and with that for 3 J hours in 4 days. The longer time 

 required in all than in Exp. No. 1 was due to the different 

 temperature of the atmosphere, the first having been carried 

 on in hot weather, and this in cold. 



It follows then that with the fullest possible concentra- 

 tion of the carbolic vapour at ordinary temperatures an 

 exposure of more than 8 J hours is necessary to ensure the 

 destruction of the bacteria. As the conditions, in ordinary 

 measures for disinfecting the air of a room by means of car- 

 bolic acid, can scarcely be made so favourable as in a closely- 

 corked bottle, it must be evident that, as generally used, 

 carbolic acid is useless for the purpose. To bring out this 

 satisfactorily, however, I performed the following supple- 

 mentary experiments. 



(5.) A tin of carbolic powder was taken, and all the per- 

 forations in the lid opened. The powder was then shaken 

 up and two pieces of the paper left suspended close above it, 

 one for 10 and the other for 24 hours. The solution into 

 which they were put became opalescent with both in 3 

 days. 



(6.) Two pieces were sprinkled freely over with the car- 

 bolic powder, and left uncovered for 10 and 24 hours respect- 

 ively. With both the solution remained perfectly clear 

 after 14 days. The powder was therefore good and showed 

 itself useful when applied in substance, but the result of the 

 whole series is to show that leaving vessels containing car- 

 bolic acid or this carbolic powder in a room is useless as a 

 measure for destroying contagion, and may indirectly be 

 harmful by giving a false sense of security, and thus pre- 

 venting the use of more efficient measures. 



II. — Experiments with Sulphur Fumes. 



(1.) One piece each exposed for 5 and 15 minutes to the 

 fumes of sulphurous acid obtained by throwing sulphur on 

 hot charcoal. The paper was suspended from a wooden box 

 inverted over the vessel containing the charcoal pan, which 

 was placed at the opposite corner. The box was not very 

 close, and the fumes escaped freely. The solution contain- 

 ing the piece exposed for 5 minutes became cloudy in 60 

 hours; that with the 15 minutes piece remained trans- 

 parent. 



(2.) Two pieces again in a closer box, but without very 

 copious evolution of fumes, one for 5 the other for 10 minutes. 



I 2 



