75 
HYDROCYANIC ACID GAS NOTES. 
By CHARLES P. LounsBurRy and C. W. MALLY, Capetown, South Africa. 
_ The submittal of these notes is prompted by the increasing employ- 
ment of hydrocyanic acid gas as an insecticidal agent in closed build- 
ings other than for the destruction of insects accompanying nursery 
stock. Of late we note recommendations in American rural papers 
for its use in dwellings to destroy bedbugs, the strengths mentioned 
being those ordinarily employed for seale insects. Seale insects, we 
have found, are exceptionally easy to destroy by the gas, and there- 
fore our experiences in the treatment of more resistant insects and 
some miscellaneous tests we have made may have interest to Ameri- 
can workers. 
The gas has been regularly used during the past two and a half 
years to effect the destruction of vermin in the sleeping coaches on 
the various systems of the Cape government railways. With the 
adoption of this treatment, complaints from bug-bitten passengers, 
before very frequent, abruptly ceased. On recent inquiry it was. 
ascertained that the railway management remains perfectly satisfied 
with the measure. Bugs are no longer found, but the coaches are 
treated once in about four months. Two 1-pound charges of 98 per 
cent of cyanide are used to a coach and the exposure continued from 
two to four hours according to the length of time available for the 
work. Two pounds to a coach is about equivalent to an ounce to 
every 80 cubic feet. 
Many of the colonial jails swarm with vermin despite many methods 
employed to mitigate the pest. Carbolic preparations, the use of 
corrosive sublimate in whitewash and as a spray, the burning of sul- 
phur, and the liberation of sulphurous acid fumes are all reported 
inefficient. Hydrocyanic acid gas is now coming into use as a last 
resort. Under our direction several jails have been treated with sue- 
cess, and it is understood that the government will soon have arrange- 
ments complete for a regular and systematic fumigation of all the 
infested premises. The personal condition of the lower-class prisoner 
on entering is often so indescribably filthy that continual reinfesta- 
tion must be contended with; hence the expediency of regular appli- 
cations of the remedy. From 1 pound of cyanide for 1,600 cubie feet 
to 1 pound for 1,000 eubie feet is used for jail work, the relative 
amount being governed to some degree by the extent of unavoidable 
leakage, the nature of the contents that may be harboring the pest, 
and the season of the year. No trouble is spared to make a space 
tight; particular attention is paid to the roof and in ease this be of 
corrugated iron, as is common in the colony, the corrugations over the 
sills and along the ridge are stopped with plugs of burlap or plugged 
with clay. The higher the roof the greater is the care exercised in 
making it tight, thus to offset the greater upward draft of air. 
