THE ELEMENTS OF PLANT FOOD 



FIG. 14. Making Bordeaux Mixture. 



Note. Copper sulphate, or blue vitriol, has very much the same 

 general effects as iron sulphate. It is also used as a disinfectant and a 

 germicide. Because of its 

 power to destroy plant dis- 

 eases, it is used in Bordeaux 

 mixture as a spray. 



To make Bordeaux mix- 

 ture. In a wooden vessel con- 

 taining ten gallons of water 

 hang a coarse sack containing 

 two pounds of copper sul- 

 phate (CuSO 4 ) so that it is 

 just below the surface. In 

 another wooden vessel slack 

 two pounds of quicklime 

 (CaO) by adding small quantities of water till it has the consistency 

 of cream, then 'adding enough water to make five gallons. When the 

 copper sulphate has all dissolved and the milk of lime has been pre- 

 pared, strain .the milk of lime through a coarse cloth into the copper 

 sulphate solution. Mix thoroughly and apply with a spray pump. 



Reaction : CuSO 4 -f CaO -f H 2 O = Cu(OH) 2 -f CaSO 4 



Hydroxide of copper (Cu(OH) 2 ) is the active agent which makes the 

 mixture a fungicide or germicide. 



CHLORINE (Cl) 



Description and Occurrence. This is a yellowish 

 green gas with so suffocating an odor that a small 

 quantity of it in the air produces violent coughing. 

 It does not occur free in nature and is not a plant food. 

 Its presence in common salt (NaCl) gives it a very 

 extensive distribution throughout the world. 



Chlorine has a strong attraction for most of the 

 elements, but more especially for H. This attraction 

 for H enables it to break up many organic molecules 



