8 
BULLETIN 1316, U. S. DEPARTMENT OF AGRICULTURE 
market. These vary considerably in strength and composition, 
some containing the equivalent of only 1 or 2 pounds of white 
arsenic per gallon, while others contain as much as 8 pounds per 
gallon. The relative quantity and the form of the alkali used 
vary also. Some brands contain a carbonate and others the hy- 
droxide of sodium. Inasmuch as the transportation is the biggest 
cost item, it is apparent that the cheapest solution is that with the 
highest concentration of sodium arsenite. Most of the experiments 
reported in this bulletin were made with a sodium-arsenite solution 
which contained approximately the equivalent of 8 pounds of white 
arsenic per gallon. This solution is referred to as 8-pound sodium 
arsenite. 
This 8-pound sodium arsenite, according to one manufacturer, is 
made from 8 pounds of white arsenic (As 2 3 ) and about 2 pounds 
of sodium hydroxide (NaOH), with sufficient water to make a 
gallon. Each gallon weighs approximately 16 pounds. An analysis 
of a sample of this material by the United States Bureau of Chemis- 
try gave the following results (per cent) : Arsenious oxide As 2 3 , 
49.98; sodium oxide, Na 2 0, 10.01. Hypothetical combinations (per 
cent) : Sodium metarsenite, NaAsCX, 18.29; sodium acid arsenite, 
jNaH (As0 2 ) 2 , 43.34; water, 38.37; total, 100. 
As the relative amounts of alkali and white arsenic used in the 
manufacture of different brands of sodium arsenite varied consider- 
ably and as a number of railroad companies that use sodium arsenite 
to Mil the weeds along the rights of way have secured better results 
with a solution containing more alkali than is used in the 8-pound 
material, pot experiments were performed to determine the most 
effective form to use. Theoretically a number of different forms of 
sodium arsenite are possible. They vary in the ratio of sodium 
to arsenic from the orthosodium arsenite, Na 3 As0 3 , to the sodium- 
acid arsenite, NaH (As0 2 ) 2 . All of these may dissociate in solution 
to form more or less sodium hydroxide, _STaOH, and arsenious acid, 
H 3 As0 3 . 
In Table 1 the toxicity of arsenious acid, sodium arsenate, and two 
sodium arsenites are compared. Small barberry plants in 3-inch 
pots were treated with sufficient quantities of the chemicals to obtain 
the indicated concentration of arsenic in the soil moisture. 
Table 1. — Effect of arsenic applied to small barberry plants in 3-inch pots 
Concentration of 
arsenic 
Arsenious acid, 
H3ASO3 
Sodium arsenite, 
Na2HAs03 
Na 3 As0 3 -FNaOH 
Sodium 
arsenate 
50 to 200 parts per mil- 
lion. 
400 parts per million 
800 parts per million 
No injury 
do.__.____. 
No injury 
do 
.do 
No injury. 
Slight injury to leaves 
Killed 
Do. 
Do. 
do 
Killed 
Perceptible injury. . 
Killed 
Slight injury. 
do 
do 
Killed. 
This series was repeated several times with similar results. The 
concentration necessary to cause the death of the plants varied 
slightly, apparently owing to soil and atmospheric conditions, but 
the relative effectiveness of the different chemicals remained about 
the same. 
