INSECTICIDES AND EQUIPMENT FOR CONTROLLING INSECTS 19 
Caution.—Mercuric chloride is a violent poison and must be 
stored in plainly labeled containers which are marked “Poison.” 
It reacts with metals; and solutions should, therefore, be placed 
in wooden, earthenware, or glass containers. It is advisable to 
wear rubber gloves when working with this compound. 
MERCUROUS CHLORIDE 
Mercurous chloride (HgCl) is known also as calomel. It is a white 
powder insoluble in water. 
Suspensions or mixtures of calomel in water are employed for the 
control of the cabbage maggot and the onion maggot, 8 or 4 ounces 
being used in 10 gallons of water. One ounce of gum arabic is gener- 
ally added to 10 gallons of the mixture to keep the calomel from 
settling rapidly. The use of this material for the control of these 
maggots is preferable in some cases to the use of corrosive sublimate 
because of the highly toxic nature of the latter to man and animals. 
Caution.—Mercurous chloride is not generally regarded as dan- 
gerously poisonous, being commonly used, in small doses, as a 
purgative. However, it should be stored in labeled containers out 
of the reach of children and irresponsible persons, since excessive 
doses are poisonous. ; 
METALDEHYDE (SLUG BAIT) 
Chemically, metaldehyde is a polymer of acetaldehyde, namely 
OO and only recently has been manufactured in this country. 
t is available as a white powder which is insoluble in water but soluble 
in benzene and chloroform. The technical grade is available in tablet 
form. 
Metaldehyde is very attractive to slugs and snails and is used in the 
bait form for these pests. It is prepared as follows: 
IVES bene hig 0 Ce Beet cack te et Sa elt We  E — 1 ounce. 
Ifa te OLvreagd seri Se as 2 Sa Si ee ee 8 a ee 3144 pounds. 
To prepare the bait, mix the metaldehyde and the bran or bread 
crumbs and store the bait in a jar or other container until needed. 
When ready to use the material, place a portion of it in a pan and add 
water slowly, while stirring it, until the bait is moistened, yet remains 
crumbly when a handful is squeezed together. 
At dusk this moistened bait is scattered over the beds that are infested 
with slugs, as described for applying poisoned-bran mash (p. 28). 
The treatment may be repeated in 2 or 3 weeks if the snails reappear, 
or if their injury and slimy trails are discovered. 
After having eaten baits containing metaldehyde, the slugs are 
stupefied and finally die. Where the vegetation is dense and humidity 
is high, the affected snails are killed more slowly or they may recover. 
Under such conditions the following bait containing calcium arsenate 
is more effective and kills more rapidly than baits containing only 
metaldehyde: 
For small quantities For large quantities 
Catlenum:e- arsenate. 22 oe 1 ounce. 1 pound. 
VSG CON Vd Css ale ee 1% ounce. 14 pound. 
) SO eo he ee 1 pound. 16 pounds. 
NIGKISSCG2 2G BS ae ok 2 teaspoonfuls. 1 pint. 
\ GTS a ca aS Sa eee me 1 pint. 2 gallons. 
