146 DESTRUCTIVE INSECTS OF VICTORIA: 



In taking the tent off of the tree the tent is first raised up with the 

 lever until its lower edge is above the upper side of the sled, after which 

 the tent is opened and the two halves are swung around and allowed 

 to rest upon the sled, as shown in Fig. 19. The sled is then 

 drawn forward until the junction of the two halves of the tent is brought 

 opposite to the middle of the second tree, when the tent is slightly raised 

 by the lever and the two halves swung around until they enclose the 

 tree, after which they are fastened together and dropped upon the ground. 

 The hinges at the upper end of the upright post on the sled are so con- 

 structed as to allow the tent to lean either backward or forward, so that 

 its lower edge may conform to the surface of the ground. 



I have been able to make only a single test with a fumigator of this 

 kind, and it gave very good satisfaction. I am of the opinion that this 

 fumigator will prove to be both cheaper and easier to operate than either 

 of those described above. There is still need of some device by which 

 the same tent could be made smaller or larger, at the will of the operator, 

 so that it maybe made to conform to the size of the different trees. Mr. 

 Culver, the inventor, informs me that he intends to use two of these 

 fumigators, transmitting the gas from one tent to the other ; but it is 

 impossible at the present writing to say whether or not he will meet 

 with success, as no tests of this kind have as yet been made. If success- 

 ful, this method would reduce the cost of treating a tree at least one- 

 half.* 



The Gas. Among the numerous gases which I have tried none have 

 given such good results as the hydrocyanic acid gas ; even arseniuretted 

 hydrogen and sulphuretted hydrogen, which are so fatal to the higher 

 animals when respired, fail to produce the same deadly effects upon the 

 scale-insects that is produced by the hydrocyanic acid gas. 



The latter, which generated in the usual manner, by acting with 

 sulphuric acid upon potassium cyanide dissolved in water, is very 

 destructive to the foliage of the trees confined to it. To remedy this, 

 three methods are at present known, viz.: The dry cyanide process, 

 which consists of acting upon the dry potassium cyanide with sulphuric 

 acid ; the dry gas process, consisting of acting with sulphuric acid upon 

 potassium cyanide dissolved in water and passing the gas through 

 sulphuric acid ; and the cyanide and soda process, which consists of 

 mixing bicarbonate of soda with potassium cyanide dissolved in water 

 and adding the mixture to sulphuric acid. 



The Dry Cyanide Process. In my early experiments with this gas it 

 was plainly to be seen that the less water the cyanide has been dissolved 

 in the less injurious was the effect of the gas upon the tree confined in 

 it. The heat generated in the production of the gas is sufficient to 

 vaporize a considerable quantity of the water in which the cyanide has 

 been dissolved, and this aqueous vapour collecting upon the leaves would 

 condense the gas, which is very soluble in water, forming hydrocyanic 

 acid, which is very destructive to plant life. It is also probable that the 



Mr. Coquillett writes later : " The tent of the Culver fumigator is now made without a frame- 

 work, except the two arches ; this makes it both cheaper and lighter than before, permitting the 

 tent to more nearly conform to the shape of the different trees confined in it." C. V. R. 



