338 MISCELLANEOUS PRODUCTS USED IN AGRICULTURE. XVI. 



cell. Water therefore leaves the protoplasm, and shrinkage 

 occurs (" plasmolysis"), so that the vital processes of the plant 

 are interfered with, perhaps by the destruction of the con- 

 tinuity of the protoplasm. If, through differences in the 

 strength and thickness of the cell walls, this action takes place 

 more readily in such plants as charlock, &c., than in cereals, 

 this explanation would seem to he sufficient to account for the 

 facts. It receives confirmation from the discovery, quite 

 recently made, that spraying with 15 or 20% solutions of 

 sodium nitrate, ammonium sulphate, or potassium chloride 

 salts which cannot he suspected of having any chemical toxic 

 effects is also effective in destroying charlock/ 1 '- (See also 

 iron sulphate.) 



Copper ln/droxide, Cu(OH). 2 , is also largely employed as a 

 fungicide for application to vines, potatoes, and fruit trees. It 

 is usually employed in the form of " Bordeaux mixture/' which 

 is made by adding lime (best in the form of " milk of lime") to 

 copper sulphate solution. Various strengths of solution have 

 been recommended, the proportion of copper sulphate varying 

 from 12it). to 30ft>. per 100 gallons of water, that of quick-lime 

 from 8ft>. to 20ft). The lime should in all cases be first slaked, 

 made into a smooth cream w r ith water, and then poured into 

 the copper sulphate solution \vith constant stirring. For many 

 purposes it is highly important that the lime should be in 

 excess and the mixture therefore free from any dissolved 

 copper compounds, since these act corrosively upon the foliage. 

 This can readily be detected by inserting a piece of bright iron 

 or steel, when no deposit of metallic copper should form ; or 

 another easily applied test is to breathe upon the surface of a 

 portion of the mixture, when a film of calcium carbonate 

 should be formed, showing the presence of free calcium 

 hydrate. The mixture should be kept constantly stirred and be 

 applied by the sprayer as soon after its preparation as possible. 



Bordeaux mixture is largely used in the preventative treat- 

 ment of vines and potatoes and is highly effective. 



Other copper compounds used as fungicides are 



1. " Eait celeste," which is essentially armnonio-copper sul- 

 phate, CuS0 4 .4NH 8 .H. 2 0, the well-known magnificent 



* Heinrich, Jahresbericht fiber Agrieultur-Chemie, 1901, 361. 



