APPLE POWDERY MILDEW AND ITS CONTROL. 15 



PREPARATION OF THE IRON-SULPHID MIXTURE. 



The following directions are for the preparation of sufficient 

 stock iron-sulphid mixture to make 500 gallons of spray : Fill a 50- 

 gallon barrel about two-thirds full of water. Weigh out 10 pounds 

 of iron sulphate (copperas), place in a sack, and suspend in the 

 water. The iron sulphate will dissolve fairly rapidly, and when it 

 is all in solution measure out carefully 2| gallons of commercial 

 lime-sulphur solution testing 33° Baume, or 2 gallons and 3 pints 

 of a lime-sulphur solution testing 32° Baume. Slowly pour all but 

 2 pints of the lime-sulphur solution into the iron-sulphate solution 

 in the barrel, stirring the mixture vigorously with a hoe or shovel. 

 The addition of the lime-sulphur solution will produce a bulky, 

 black precipitate, and when all but 2 pints of the lime-sulphur solu- 

 tion has been added the mixture should be allowed to stand for a 

 few minutes, when the black precipitate will begin to settle and 

 a little of the clear liquid at the top can be carefully dipped out 

 with a clean glass or cup. This clear liquid will probably show no 

 yellow lime-sulphur color, which means that an excess of lime- 

 sulphur solution has not yet been added. In other words, there is 

 still some iron sulphate in solution, in which case the addition of a 

 drop of lime-sulphur solution to the clear liquid in the glass will 

 produce a black precipitate. This means that more lime-sulphur 

 solution should be added to the stock in the barrel, and about 

 half of the remaining 2 pints should now be poured in and the 

 contents of the barrel stirred vigorously and allowed to stand. Some 

 of the clear liquid should again be dipped off and tested as before, 

 to determine whether an excess of lime-sulphur solution has been 

 added. If necessary, the addition of small quantities of lime-sul- 

 phur solution should be continued until some of the clear liquid 

 dipped from the top, after the contents of the barrel have been 

 well stirred and allowed to settle, shows a pale yellowish lime-sul- 

 phur tint. The purpose of using a slight excess of the lime-sulphur 

 solution is to insure all the iron sulphate being utilized. The volumi- 

 nous black precipitate that is formed consists of iron sulphid, pre- 

 cipitated sulphur, and calcium sulphate. After a slight excess of 

 lime-sulphur solution has been added, the barrel should be filled 

 with water and the contents stirred thoroughly and allowed to stand 

 for several hours. The black iron-sulphid mixture will settle into 

 the lower half or third of the barrel, and the clear liquid should be 

 poured off by carefully and gradually tipping the barrel, without al- 

 lowing any of the black precipitate to run out. The barrel should 

 again be filled with water, the contents thoroughly stirred and al- 

 lowed to stand several hours, and the clear liquid poured off as before. 



