Bordeaux Mixture 75 



sect and disease prevention is the more 

 plausible explanation of the apparent stimu- 

 lation. Iron is a constituent of chlorophyl. 

 The rate at which Bordeaux mixture settles 

 is an important matter. Each of the com- 

 pounds I to V has a different density, is more 

 or less voluminous and settles at a different 

 rate from the others. Pickering states that 

 the volums occupied by the precipitates after 

 standing 15 minutes vary regularly and may 

 be represented, approximately, by these num- 

 bers, 8(1), 17(11), 86(111), 98(IV)*', 20(interpo- 

 lated) (V). This means that (IV), ordinary 

 Bordeaux, is the most voluminous and stays 

 in suspension best. Butler* shows that the 

 order of mixing and the concentration of solu- 

 tions at the time of mixing have a bearing 

 on length of time the precipitate stays in sus- 

 pension and reconmiends making a dilute 

 copper solution and pouring this into a strong 

 milk of lime. The directions for this exercise 

 allow the student to make the copper and lime 

 solutions of equal volum and pour one into 

 the other indiscriminately. According to 

 Butler the methods followd in this exercise 

 take second rank in producing desirable volu- 

 minous precipitates. 



* Technical Bulletin, No. 8, New Hampshire Experi- 

 ment Station; also Phytopathology, 1914. 



