36 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 
at the right and left margins are to be found blank spaces, and in the 
horizontal lines corresponding to these the numbers at the top of the 
chart are repeated in that part of the chart containing dosage figures. 
These numbers, repeated in this manner, make it easier for the eye 
to locate with certainty the dosage figures sought. In the chart used 
by the writer the figures representing distances around and over are 
printed in red. The lines bounding these columns of figures are also 
red. All the rest of the lines and figures are black. 
The writer does not maintain that this table is accurate to the 
minutest part of an ounce for every dosage, but that such variations 
as do exist are so small that in practical work in the field the results 
in killing scale insects will be found uniformly satisfactory through- 
out. Two years of experience with the outfits belonging to this 
investigation, as well as with many practical outfits, in which work 
thousands of acres have been fumigated, have proved that this 
belief is well founded. 
It is a common practice with tent-pullers in covering small trees 
to kick in the edge of the tents little if any so as to prevent as much 
as possible the generator as well as the escaping gas from coming in 
contact with the tent. This common practice leaves much more 
space under the tent and incidentally makes more leakage surface in 
small trees than was provided for in the original chart. (Bulletin 
No. 79, fig. 28, p. 65.) To correct this feature of the fumigation 
practice, the original chart has been revised by increasing the smaller 
dosages to the extent which in field practice has been found necessary. 
In this revised chart the half ounces are not used as in the original. 
Field experience has taught that it is desirable to have schedules as 
simplified as possible. The writer would now advise all fumigators 
to discard all old schedules and to use the revised one entirely. The 
dosage strength on which this schedule was based was calculated for 
use against the purple scale. However, this does not imply that it may 
not be used against other insects; in fact, the greatest advantage 
of it is that it can be manipulated so as to meet the requirements for 
use against any insect. The schedule in its original form is not recom- 
mended for use against all insects under all conditions, as many have 
believed. Some of the scale pests frequenting citrus trees require 
a heavier dosage for their destruction than others. The first point 
to be determined is the strength of gas required for a particular pest 
under its special conditions. When this is known, then schedule 
No. 1 can be manipulated to meet the requirements, provided it is 
not already of the proper strength. This change is secured by 
increasing or decreasing all the dosages throughout schedule No. 1 at 
the same rate, i. e., J, J, I, etc. The resultant schedule will be one 
of uniformity even as is the original. So in treating an orchard the 
first point to determine is what species of insect has to be combated. 
