14 BULLETIN 160, U. S. DEPABTMENT OF AGBICULTUEE. 



ployed. On April 13, 1914, 1 pound of lead arsenate in the paste form 

 "was placed in 20 gallons of cactus water which contained copper 

 sulphate in the amount of 1 pound to 28 gallons of water. It was 

 at once noticed that the copper sulphate retarded the precipitation 

 of the lead arsenate, so much so that the solution could be used as 

 a spray with some success, at a normal pressure with a hand pump. 

 This was encouraging, as it had been impossible to use lead arsenate 

 alone in combination with cactus as an adhesive. The writer would 

 recommend, however, that the foregoing combination be used on 

 a large scale only when a strong pressure can be maintained through- 

 out the operation, or the results will be unsatisfactory. 



The mortality in the experiments was practically the same as 

 when the arsenical was used alone. Had more experiments been 

 made in the field, in all probability a higher mortality would have 

 been observed in the end. 



COPPER SULPHATE AND FERROUS ARSENATE. 



The use of copper sulphate as a preservative for the cactus, com- 

 bined with ferrous arsenate to form a spray, did not appear to pro- 

 duce any chemical changes, no noticeable precipitate being found 

 that would prevent the use of the solution as a spray. It had been 

 expected that more of an action would take place when the ferrous 

 arsenate was added to the cactus water containing copper sulphate. 

 The ferrous arsenate was not altered in insecticidal value when mixed 

 with sulphate of copper. 



EXPERIMENTS WITH OTHER PRESERVATIVES. 



SALICYLIC ACID. 



On March 13, 1914, 45 pounds of cactus were sliced and placed in 

 32 gallons of water, and in another lot 30 pounds were added to 24 

 gallons of water. The following day the solid portion of the cactus 

 was removed from the two lots and the water poured from both into 

 another receptacle. This made 56 gallons of the liquid to be pre- 

 served. One-fourth of a pound of salicylic acid was dissolved and 

 added to the cactus water, and the mixture was allowed to stand 

 exposed to the air. On April 1 the mixture was found to be in per- : 

 feet condition. A bluish-white scum was noticed to have formed on 

 the surface shortly after the acid was dissolved in the water. To 

 dissolve salicylic acid a certain amount of alcohol is necessary. At 

 first the acid was dissolved in a 10 per cent solution of alcohol, but 

 it was later found that cactus water served equally well for this 

 purpose after fermentation was well under way, although action 

 was somewhat delayed. 



