Circular 21 - Insecticides and Subsidiary Materials 58 
pyrethrum spray has to be prepared with hard 
or salt water or v/hen the finished spray is 
applied to the surface of vi^ater pools and 
marshes having a salt content higher than 5 
percent, to kill mosquito larvae. 
Orvus W. A. is a proprietary product 
knovm chemically as sodium lauryl sulfate. 
It comes prepared in the form of paste or 
flakes in 25-pound cartons, the paste costing 
30 cents per pound and the flakes 53 cents 
per pound, 
For manufacturer and distributor 
see number 92 of list at end of this circular. 
P-\RAD ICKLOROBEInIZENS 
Paradichlorobenzene is used as a soil 
fumi2;ant to kill various insect pests, and as 
a repellent and furaifant for such fabrics 
pests as clothes moths and carpet beetles. 
Recent results indicate that it is not alv/ays 
effective as a soil poison for termite con- 
trol, hence it is not recommended for this use 
Chemically, this material (C^HyClp) is 
a white, crystalline coiauound which vola- 
tilizes slowly. The vapor formed is nonin- 
f lai:iiaable , penetratinr, and has a sumev/hat 
ether-like odor. It is not explosive nor 
dan.-^erous to handle. It is marketed in the 
form of crystals or in cakes, and is obtain- 
able in any quantity desired. 
Paradichlorobenzene should be stored 
in air-ti;:ht containers to avoid loss by 
evaporation. 
