178 
kinds of scale insects are quite as susceptible to its influence daring 
cool weather, or at night, as they are at any other time. 
It will, of course, be quite impossible to lay down any fixed rule in 
relation to the proper quantity of the chemicals to be used on any 
given tree. Experience has shown that a tree possessing a dense 
foliage will withstand unharmed a much stronger dose of the gas than 
will a thinly-foliaged one. the .supposition being that in the former case 
the gas is distributed to such a great number of leaves that its effect 
upon each leaf is nut so severe as would be the case if there were 
fewer leaves to receive it. In a general way. we may say that each 
ISO cubic feet of space inclosed by the tent will require one ounce of 
cyanide and the other materials in the proportions given above. 
The material commonly used in the construction of the tents tor in- 
closing the trees is what is known as -eight-ounce duck." At first it 
was the custom to manufacture this into bell-shaped tents, but experi- 
ence has shown that simple sheets will answer the purpose quite as 
well as tents, besides being less expensive and much easier to remove 
from the trees. These sheets are made in the form of an octogon. 
since it requires less labor and there is less waste of material in con- 
structing them of this form than would be the case if they were made 
circular. 
In the case of very large sheets, it is customary to use a heavier 
material for the two middle breadths, since it is on this part of the 
sheet that the principal strain falls in placing the sheet upon the trees 
and in removing it again: for these two breadths the ••ten-ounce duck" 
is used. 
Several tests made with unpainted tents prove that it is not desira- 
ble to use them in this condition, since they permit of the escape of a 
large quantity of the gas. and in order to render them gas-tight they 
are painted over with linseed oil. with or without the addition of 
other substances. Among such substances may be mentioned yellow 
ocher. lampblack, sizing, whiting, beeswax, and soapsuds. Perhaps 
the substance most commonly used is a thin paint made from yellow 
ocher. this being lighter in weight and less expensive than most other 
paints. It would, of course, be very desirable to employ some kind of 
ready-prepared cloth in the construction of the tents, but thus far my 
efforts at obtaining such material have not been successful. The near- 
est approach to it is a rubber cloth, but even the cheapest grade of 
this is almost three times as expensive as the painted cloth described 
above. 
In regions where cactus abounds, the mucilaginous juice of this plant 
may be used in place of linseed oil; the cactus is simply cut into small 
pieces, thrown into a barrel, and covered with cold water: after stand- 
ing for a day or two it is ready for use. 
Where the trees are less than twelve feet in height, the sheets can 
be placed over them and removed again by the use of poles, but on 
