3 



(1) Na 2 C0 8 .10H 2 O + As 2 0 3 = Na 2 0. As 2 0 3 + C0 2 + 10H 2 O 



(2) 2NaOH + As 2 0 3 = Na 2 0. As 2 0 3 + H 2 0 



(3) Na 2 C0 3 .10H 2 O + 2As 2 6 3 = is T a 2 0 .2As 2 0 3 + C0 2 + 10H..O 



(4) 2NaOH + 2As 2 0 ;! = Na 2 Q .2As 3 b s + H 2 0 



Equations 1 and 2 represent proportions for the formation 

 of the neutral salt. By calculating from these two relationships it 

 appears that it will require approximately 1.5 pounds sal soda or 

 only 0.4 of a pound of caustic soda to react with 1 pound of white 

 arsenic to form neutral sodium arsenite. Equations 3 and 4 

 represent the proportions at which the two react to form the 

 acid salt. From these it can be shown that approximately 1 pound 

 of sal soda combines with 1% pounds of arsenic, and 1 pound of 

 caustic soda combines with 5 pounds of arsenic to form the acid 

 salt, 



The effectiveness of the two salts as weed destroyers is very 

 much the same. However, from an economical standpoint the 

 neutral salt which has given excellent results upon most weeds is 

 as follows 4 : 



2 pounds sal soda 

 1 pound arsenic 

 1 gallon water. 



Boil this mixture until clear, then dilute to about 24 gallons 

 for spraying. Instead of 2 pounds sal soda, 7 ounces of caustic 

 soda will produce the same results. However, the use of the latter 

 salt involves a certain degree of danger to the laborers who may 

 be required to handle it while the sal soda is practically harmless. 



On Olaa plantation where the use of poisonous sprays has 

 been given a thorough test the acid sodium arsenite is in use. The 

 following formula has been adopted and is very effective : 

 20 pounds arsenic 

 4 to 5 pounds caustic soda 

 10 gallons water. 

 This mixture is boiled for 10 to 15 minutes and the whole 

 diluted to 400 gallons. Instead of 4 pounds caustic soda approxi- 

 mately 13 pounds sal soda would be required. 



Effect on plant growth. 



In order to gain some information with reference to the effect 

 of arsenite of soda upon plant growth a series of pot experiments 



