INSECTICIDES 491 



for commercial work. It is prefera])le to dilute the copper 

 sulfate solution. Never pour together the concentrated stock 

 mixtures and dilute afterward. Bordeaux mixture of other 

 strengths as recommended is made in the same way, except 

 that the amounts of copper sulfate and lime are varied according 

 to the requirements. 



It is not necessary to weigh the Hme in making Bordeaux 

 mixture, for a simple test can be used to determine when enough 

 of a stock hme mixture has been added. Dissolve an ounce of 

 yellow prussiate of potash in a pint of water and label it " poison." 

 Cut a V-shaped sUt in one side of the cork so that the Hquid 

 may be poured out in drops. Add the lime mixture to the di- 

 luted copper sulfate solution until the ferrocyanide test solution 

 will not turn brown when dropped from the bottle into the mix- 

 ture. It is always best to add a shght excess of hme. 



Fumigation 



The fumes of hydrocyanic acid gas are very destructive to 

 insect hfe. Fumigation with this gas is practiced extensively 

 in greenhouses, in citrus orchards, where the trees are inclosed 

 in portable tents for the purpose, and for the destruction of scale 

 insects on nursery stock. 



Hydrocyanic acid gas is a deadly poison, and the greatest 

 care should be exercised in its use. For generating the gas 

 always use 98 to 100 per cent pure potassium cyanide, and a good 

 grade of commercial sulfuric acid. The chemicals are always 

 combined in the following proportion : 



Potassium cyanide 1 ounce 



Sulfuric acid 1 fluid ounce 



Water 3 fluid ounces 



Use an earthen dish, pour in the water first, then add the 

 sulfuric acid to it. Put the required amount of cyanide into a 



