TEEATMENT OF DISEASES INJURIOUS TO ORCHARD CROPS. 73 



a saturated solution of the copper sulphate, and thus avoid the delay of 

 dissolving the copper sulphate each time the mixture is made. At 

 ordinary temperatures the saturated solution contains about three poimds 

 of copper sulphate per gallon,* and for all practical purposes in making 

 Bordeaux Mixture it may be reckoned at that amount. It is then easy to 

 calculate how much of such a solution must be taken to get the number 

 of pounds of copper sulphate which is called for by the formula. 



The lime may be kept on hand slaked and ready for use, if after it has 

 been slaked the air is excluded. This may be done by keeping it covered 

 with water ; it will then keep indefinitely in good condition. The 

 weighing of the lime to determine the amount required by the formula is 

 ob\dated by using a simple colour test, which shows instantly whether 

 enough lime has been added to combine with all of the copper sulphate. 

 This, which is known as the potassium ferrocyanide test, has successfully 

 stood the trial of practical use for several years. 



Insecticides. 



Combining Insecticides and Fungicides. — The cost of treatment with 

 fungicides and insecticides may be much reduced when both can be 

 applied at one operation. For perhaps ten years or more it has been a 

 common practice to combine the arsenical insecticides with Bordeaux 

 Mixture when both are needed. 



Substitutes for Paris Green. — Paris Green long held front rank as an 

 arsenical insecticide. It is decidedly more expensive than other arsenical 

 poisons, and some of these are now being substituted for it in many 

 places and in increasing quantities. Prominent among these may be men- 

 tioned a green arsenite of copper, which represents about the same amount 

 of arsenious oxide as Paris Green and is used pound for pound in place of 

 that substance as an insecticide. It has the advantage of being much 

 cheaper than Paris Green, and it is also better adapted for use in a spray 

 mixtm-e, because being an amorphous, impalpable powder, instead of 

 crystalline, it stays much longer in suspension in liquid mixtm'es than 

 does Paris Green. 



A still cheaper and equally efficient arsenical insecticide is a home- 

 made preparation of sodium arsenite. It is made by boiling white arsenic 

 in sal. soda (sodium carbonate) till it dissolves. It may then be bottled 

 or otherwise kept from evaporating, and may be used in all formuhi? in 

 place of Paris Green. So much of the liquid as represents one pound of 

 white arsenic is taken in place of two pounds of Paris Green. Milk of 

 lime should be added to prevent injury to the foliage unless it is combined 

 with Bordeaux Mixture. 



One of the best arsenical insecticides, doubtless, is arsenate of lead. 

 For the addition of this to the list of insecticides we are indebted to 

 another insect foe, namely, the gypsy moth. This insect was introduced 

 into Massachusetts from Europe not many years ago. For fighting this 

 terrible pest the State of Massachusetts has already appropriated an 

 aggregate equivalent to more than £200,000. The experiments of the 



* At 59° F. a gallon of saturated copper sulphate solution contains about 49 oz. 

 of copper sulphate. 



