DESTRUCTION OF BACTERIA. 25 
to add to its disinfecting action. Solutions of 50 to 
70 per cent, are the best. The use of alcohol is 
limited. Perhaps its greatest usefulness is in destroy¬ 
ing bacteria in the skin, although even for this it is 
rarely depended upon alone. 
Of the disinfectant gases only the two most often 
used need be mentioned: Sulphur-dioxide gas is made 
by burning roll sulphur in the presence of water vapor. 
The vapor is essential because the disinfectant action 
depends upon the formation of sulphurous acid, which 
is made by the combination of the water vapor with 
the fumes of sulphur. It requires about 8 pounds of 
sulphur for every 3000 cubic feet of air space, and it 
should be allowed to act for at least twenty-four hours. 
It is a surface disinfectant having very little pene¬ 
trating power, and is not as reliable as it was once 
thought to be. It is liable to corrode fabrics and 
destroy colors. It tarnishes metals and leaves a dis¬ 
agreeable odor for some time after it is used. 
Formaldehyde gas is made in a variety of ways. 
For use in hospitals and by boards of health an auto¬ 
clave is used, which generates the gas under pressure. 
After the room has been sealed to prevent the gas 
from escaping, the gas from the autoclave is forced 
into the room through the keyhole of the door. A 
much simpler way that is practical for home disin¬ 
fection is the burning of paraform candles in the pres¬ 
ence of moisture. The disinfectant action is strongest 
when the temperature of the room is between 90° and 
ioo° F. The gas is a surface disinfectant; conse- 
Disin- 
fectant 
gases 
