38 



FUMIGATION INVESTIGATIONS IN CALIFORNIA. 



From the following chart it is evident that with the acid and cyanid 

 mentioned the largest amount of gas is available from two parts of 

 water. As the proportion of water is increased above two parts the 

 available gas is decreased until with eight parts of water we obtain 

 only about 4.3 per cent of gas, or less than one-half as much as with 

 two parts. In other words, 1 ounce of cyanid and 1 ounce of acid in 

 combination w^itli 2 ounces of water will produce much more avail- 

 able gas than 2 ounces of cyanitl and 2 ounces of acid with 16 ounces 

 of water. 



The cause for the smaller amount of gas w^ith one part of water 

 than with two parts has already been explained (see p. 35). 



We can see from the chart that the proportion of water used is one 

 of the most important factors in fumigation practice; and many of 



p/?opoffr/o/v5 Of 



CyAMO\ ACID WAT£fi 



PER C£A/rOF G/tS 6/i^£A/ OPT 



10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 



Fig. 13.— Chart showing total amount of gas evolved when difTerent proportions of water are used. 



(Original.) 



the poor results in field work can be directly attributed to the use of 

 too much water. That the water should be measured as carefully as 

 the acid is beyond question. 



Aside from variations in the amount of water used, due to lack of 

 precision in measuring, the proportion of water recommended by dif- 

 ferent authorities on fumigation has varied all the way from two to 

 eight parts. It is no wonder we see widely differing results from the 

 work of diflferent men. It is a common practice w^ith many fuini- 

 gators to increase the dosage when fumigating a tree that is severely 

 infested with scale. It is also a common practice — in fact, so com- 

 mon as to be almost universal — to increase the pro]K>rtion of w^ater 

 when using heavy dosages. This is apparently done with a view to 

 preventing injury to the fruit and foliage. In following out this prac- 

 tice the fumigator has many times unconsciously prevented the very 

 result he washed to accomplish — that of obtaining a more concen- 

 trated gas. 



THE CORRECT PROPORTION' OF WATER. 



The chart (fig. 13) shows that two parts of w^ater to one part 

 each of cyanid and acid will })roduce the maximum amount of avail- 



