148 



DESTRUCTIVE INSECTS OF VICTORIA: 



once takes place, and the gas is rapidly given off in the form of a dense 

 whitish fog, resembling smoke and possessing a peculiar odour. When 

 the gas, diluted with air, is inhaled, it produces a dryness in the mouth 

 and throat. 



It is impossible to give any definite rule for using the different ingre- 

 dients that will apply to the differently sized trees, owing to the fact 

 that trees of the same height may have a varying diameter of top ; thus 

 orange trees 12 feet tall may have a diameter of top ranging all the way 

 from 6 to 10 feet. The manner in which the tree is pruned will also 

 make a difference in the quantity of the ingredients to be used, some 

 trees being allowed to branch almost from the ground, while others are 

 trimmed up from 3 to 5 feet from the ground. 



The following table, based upon numerous experiments which I have 

 made on orange trees under a tent 10 feet tall and having a transverse 

 diameter of 10 feet, will give a good idea of the proper quantities of 

 each inofredient to be used in treatius; citrus trees : — 



This table is based upon the cubical contents of the space enclosed 

 by the tent, supposing that the lower part of the tent rests upon the 

 ground. No harm will result to the tree if twice the quantity that I 

 have recommended be used, but of course, for the sake of economy, it 

 will be desirable to use only siach quantity of each ingredient as will be 

 necessary for destroying the scale insects infesting the tree to be treated 

 with this gas. The sulphuric acid should have a density of 65° when 

 tested with an acid hydrometer ; should its density be lower than this, 

 use an extra ounce of the acid for every five degrees of density below 

 65°. 



The Cyaniole and Soda Process. — The third method of rendering 

 the hydrocyanic acid gas harmless to the foliage of the trees confined in 

 it consists of mixing this gas with carbonic acid gas, the latter having 

 the property of extacting the moisture from the former, forming gaseous 

 carbonic acid. This appears to occur only under a certain degree of 

 pressure ; thus, if the two gases are generated in the same open 

 generator within the tent and allowed to rise and fill the tent, the 

 hydrocyanic acid gas will prove nearly as injurious to the foliage of 

 the tree confined in it as it would if no carbonic acid gas had been 

 present. 



