18 MISC. PUB. 526, U..S. DEPT. OF AGRICULTURE 
deciduous foliage do not follow a sulfur spray with sprays contain- . 
img oi until all sulfur residues have disappeared. 
Directions for the preparation of self-boiled lime and sulfur and 
home-boiled lime-sulfur concentrate may be obtained from the county 
agricultural agent, the State experiment station or State entomologist, 
or the United States Department of Agriculture. — 
Caution.—Lime-sulfur sprays are very caustic to the skin, espe- 
cially at the strengths used in the dormant season. Persons ex- 
posed to this material should protect their faces by covering them \ 
with grease or vaseline before they begin spraying, and should 
avoid getting any of the material into the eyes, where it will cause 
acute temporary discomfort. Don’t allow lime-sulfur spray to 
drift onto painted buildings, or a very unsightly stain may result. 
MAGNESIUM ARSENATE 
Several compounds of magnesium oxide and arsenic oxide are 
known, and it has been reported that the commercial product 
sold as “magnesium arsenate” contains the dimagnesium salt, 
MgHAsO,, and two basic salts, principally one having the composition 
Mg;,(AsO.)..MgO.H.O. There is also present a large excess of magne- 
sium oxide or hydroxide, which is necessary to keep down the content 
of water-soluble arsenic. 
Magnesium arsenate is a white powder but is colored pink when 
packaged as an insecticide to indicate its poisonous nature. It is used 
as a spray, at the rate of 4 pounds in 100 gallons of water, against the 
Mexican bean beetle. Derris and cube have largely replaced it for the 
control of this insect, but it can be used. where these are not available, 
provided application is discontinued when the bean pods start form- 
ing. Magnesium arsenate is not used for the control of other insects. 
Its tendency to injure foliage is one drawback to its extensive use. 
Caution.—Magnesium arsenate, like all arsenicals, is a poison- 
ous compound and should always be so labeled, and stored away 
from ali food products and out of the reach of children. For 
spray-residue tolerance, see page 3. 
MERCURIC CHLORIDE 
Mercuric chloride (HgCl,) is known also as corrosive sublimate and 
as bichloride of mercury. It is soluble in water, but dissolves slowly 
unless the water is heated. Commercially it is available as a white 
powder, as crystals, and in the form of 7.5-grain tablets. The powder 
form is used commonly for insecticidal purposes. 
A solution of 1 ounce in 714 gallons of water or 1 level teaspoonful 
in 10 quarts of water, or two 7.5-grain tablets to 1 quart of water 
(1: 1,000) is prepared by dissolving the compound in a small quantity 
of hot water and diluting it with cold water. This solution is used in 
the control of fungus gnats, earthworms in greenhouses, and the cab- 
bage maggot. ‘To avoid injury to the plant, keep the solution off 
of the foliage. Mercuric chloride is also used for the treatment of 
dormant gladiolus corms to controi the gladiolus thrips. Other 
common uses are as a fungicide and a germicide. 
