276 QUEENSLAND AGRICULTURAL JouRNAL.. [1 Apnrit, 1899. 
The charging of the tents or generation of the gas is done as follows :— 
Having calculated the cubic contents of the tree, say 1,200 cubic feet, you allow 
1 oz. of cyanide of potassium, 1 fl. oz. of sulphuric acid, and 3 fl. oz. of water to 
every 300 cubic feet of space; that is to say, for 1,200 cubic feet, you will 
require 4 oz. of cyanide of potassium, 4 fl. oz. of sulphuric acid, and 12 fi. oz. 
of water. You first place the 12 fl. oz. of water in an earthenware dish (a 
pudding-basin answers very well); then add the sulphuric acid to the water, 
taking care to pour it on slowly and not to splash, as the acid will burn holes in 
the clothes or injure the face, arms, or hands of the operator if not carefully 
used. The basin containing the acid and water is next placed under the sheet 
or tent, as far from the canvas as possible. The cyanide is then added, and a 
small piece of sacking is placed over the basin to prevent spurting. The 
operator takes especial care not to breathe whilst under the tent, after having 
added the cyanide to the acid and water, and gets out as quickly as possible, 
the bottom of the sheet or tent being made air-tight as soon as he has got out. 
The gas is generated very rapidly, and is a deadly poison, all scale or other insects 
breathing it being killed. The trees remain covered for 45 minutes, when the 
sheets or tents are removed to other trees. Ona quiet night, especially when using 
large doses, it is advisable to take care when raising the sheets and tents to let 
the gas diffuse for a short time before going too near the trees, as although 
there is comparatively little danger in breathing the gas when well mixed with 
air, yetif too muchis inhaled it 1s apt to cause a severe headache. 
Great care has to be taken to prevent the acid from spurting or splashing 
on to the sheets or tents, as it destroys the material at once. All holes have to 
be mended, and for this purpose we have found that a rubber cement made by 
Mr. Cox, of Albert street, Brisbane, answers admirably. A small piece of 
duck is placed over the hole, and is firmly and quickly attached to the sheet by 
means of the cement. Care is also required not to pack the sheets away when 
damp, and to keep all poles; blocks, and tackle in good order. The cyanide of 
potassium, being a deadly poison, should always be kept under lock and key, and 
the sulphuric acid should always be handled with great care. When handling 
the cyanide, keep the finger-nails cut short so as to prevent the poison from 
accumulating beneath them, and wash the hands carefully before eating, as the 
poison is so deadly (under 8 grains being a fatal dose) that every possible 
precaution should be taken to prevent even the smallest particle getting on to 
the food. 
Demonstrations of this method of treatment have already been given to 
the fruitgrowers of Mount Cotton, Zillmere, Bald Hills, and North Pine; and 
further demonstrations will be given in the Maryborough district within the 
next few days. In carrying out the experiment work, I have been abl 
seconded by Messrs. Voller and Henderson, and the following table is the work 
of the latter officer. 
As previously stated, this table is only approximate, and the quantities 
are based on the assumption that 1 oz. of 98 per cent. cyanide of 
potassium, 1 finid oz. of 98 per cent. commercial sulphuric acid, and 3 fluid 
oz. of water are required for every 300 cubic feet of space enclosed. This 
proportion is the same as that used by the Cape Colony authorities, with the 
exception that we use one-half more water, as we have found the extra water 
to be anadyantage. Used at this strength, we have not found the gas to 
injure the trees in the slightest, and in the case of trees badly infested with 
Pink Wax and Red Orange Scale, we have used the gas one-half stronger—viz., 
1 oz. of cyanide, &c., to 200 cubic feet of space; and even at this strength we 
have only found the younger shoots of oranges, lemons, and mandarins slightly 
burnt. Many varieties of mangoes stand an even greater strength during the 
winter months, and in the case of badly infested trees especially, if they are 
not making growth, I shall use the greater strength so as to be certain of 
