296 INSECTICIDES AND FUNGICIDES 



the fungicidal value of the spray. Leaf injury is due to too 

 concentrated a solution of the sulphides. Lime-sulphur 

 may be mixed with lead arsenate, but unless the triplumbic 

 form of the latter is used, leaf injury may result due to the 

 formation of a soluble arsenic compound. Miscible Oils 

 are the result of an attempt to dilute crude petroleum so 

 that it can be used with safety to plants. The result is 

 accomplished by making what is essentially a soft carbolated 

 soap called the "emulsifier." This is mixed with crude 

 petroleum, paraffine oil, or rosin oil, and a "miscible" oil 

 is formed. When this is mixed carefully with water in any 

 proportion a milky emulsion is produced that is reasonably 

 permanent. 



For fungi the plants must be sprayed at the proper time 

 to kill the spores of internal fungi, or at any convenient 

 time to kill external fungi. Copper salts make excellent 

 fungicides, but the soluble salts are injurious to leaves, 

 hence it is customary to use a compound of copper 

 which is ordinarily insoluble, but which dissolves slowly 

 enough under atmospheric conditions to kill fungi. It 

 is only soluble compounds which are actually injurious 

 to fungi. Bordeaux mixture is such a suspension. It is a 

 complex, double basic copper calcium sulphate from which 

 copper sulphate gradually forms under the action of water 

 and carbon dioxide. It is sometimes harmful to vegetation 

 on this account, especially when atmospheric conditions are 

 aggravating and there is not enough lime present. For- 

 maldehyde is a gas which dissolves readily in water and can 

 be easily obtained in solution. From the solution form- 

 aldehyde can be generated in a number of ways and thus 

 be used where a spray could not reach. Lime-sulphur boiled 

 has been mentioned. Lime-sulphur self boiled is a mechanical 

 mixture of slaked lime and sulphur with some sulphides of 

 calcium. It is made by mixing sulphur with slaking lime 

 and the heat of slaking boils the mass. Too long boiling 

 forms more of the sulphides than are desirable to use at the 

 strengths employed. 



