14 



As indicated by the origiual formula given above, two-thirds 

 of a pound of lime has been found to be sufficient to neutralize 

 a pound of blue vitriol. For convenience we have used and 

 recommended equal weights of blue vitriol and lime. We do 

 not know of any l)ad results from using this amount of lime. 



Instead of weighina: the lime a test has been in use during 

 the past year or two which indicates when sufficient lime has 

 been used. This test consists in adding a few drops of a solu- 

 tion of yellow prussiate of potash, or potassium ferrocyanide, as 

 it is known chemically, to the Bordeaux mixture, when a brown- 

 ish color will appear if too little lime has been used. More lime 

 must then be added until the brown color fails to appear on 

 adding a fresh quantity of the ferrocyanide solution. This test, 

 when rightly used, is probably reliable. Instances are however 

 •reported of the Bordeaux mixture causing injury to foliage and 

 fruit where this test has been used, probably from the fact that 

 not quite enough lime had been used. It is therefore recom- 

 mended that after the addition of the ferrocyanide solution ceases 

 to produce the brown color, a still further quantity of lime 

 should be added for safety, for a small excess is far better than 

 a slight deficiency. Perhaps, under the circumstances, it would 

 be safer to continue to weigh the lime, using two-thirds as much 

 as of blue vitriol. 



Perfectly fresh lime should be used. Air-slaked lime will not 

 answer. It is therefore better to use only the lumps. Care 

 should be exercised in slaking the lime. Water should be ad- 

 ded only just fast enough to keep the lime wet. It should be 

 kept thoroughly stirred after it begins to slake, as when any 

 considerable quantity is used the bottom poi'tions are apt to be- 

 come dry and " burnt." After the lime is slaked, sufficient water 

 should be added to make it of the consistency of fresh cream. 

 It is then ready to be added to the solution of blue vitriol. The 

 blue vitriol may be dissolved quickly in hot water, or the re- 

 quired amount may be placed in a basket or loosely woven 

 sack and suspended in a tub or other wooden vessel of cold 

 water. As fast as it is dissolved the solution, which is heavier 

 than the water alone, will sink to the bottom of the vessel and 

 a fresh portion of water will come in contact with the crystals 



