270 THE AMERICAN MONTHLY [Oct 
dioxid to form sulphurous acid, which is the real disin- 
fecting agent. Dry sulphur dioxid has practically no ef- 
fect upon bacteria. Our work has shown that very small 
atmospheres of the dry gas will quickly destroy mosqui- 
toes, and we therefore believe that the destruction of 
these insects may be accomplished in dwelling houses with 
little danger of injuring fabrics or tarnishing metals. 
Sulphur dioxid is so far superior to furmaldehyd as an 
insecticide that even the risk should not outweigh the 
certainty of its action. The gas may now be obtained in 
its liquefied form, either in tin cans, in syphons, or in iron 
cylinders, affording very convenient methods of quickly 
introducing a given amount of the dry gas into an in- 
closure. 
A series of experiments was also made to determine 
whether chemically dry sulphur dioxid has insecticidal 
properties. It is well known that the anhydrous gas has 
practically no effect upon bacteria. As the dry gas is 
not destructive to fabrics and metals, it is of considerable 
practical importance to know whether it will kill mosqui- 
toes. 
To this end the liquid sulphur dioxid was liberated in 
a bell jar, but first passed through 2 drying columns con- 
taining pumice stone saturated with sulphuric acid. The 
moisture contained in the air of the bell jar was elimi- 
nated in 2 ways, (1) by drawing air through the drying 
columns into the bell jar, or (2) by introducing calcium 
chlorid into the bell jar. It was found, in all these tests, 
that the mosquitoes were killed, practically instantly, by 
the dry gas. 
Contrary to formaldehyd, which requires an exposure 
and strength of gas sufficient to destroy spores in order 
to entirely rid a room of mosquitoes, sulphur dioxid will 
kill these insects even when the quantity of the disinfect- 
ant and the time of exposure are reduced so that non- 
spore-bearing bacteria are unharmed. Sulphur dioxid 
