INSECTICIDES, FUNGICIDES AND DISINFECTANTS 219 



but its period of activity is of short duration, due to the 

 fact that it is quickly washed off the plant. Copper sulphate 

 is very successfully used for the destruction of algae in water. 



Ammoniacal copper carbonate (Cu(NHs)4C03) is used 

 in special cases on ornamental plants and on certain fruits 

 just before ripening, where residues from other sprays 

 would be objectionable. The chief objections to this prep- 

 aration are its relatively high toxicity to the host plant, 

 its cost, and the difficulty of its preparation. 



Formaldehyde solutions (CHaO) are chiefly used for the 

 treatment of seeds and vegetable reproductive materials, 

 as tubers, to rid them of disease before planting. The 

 solution is prepared by adding 1 pint of formalin to 30 gal- 

 lons of water. 



164. Common Disinfectants. Disinfectants are used to 

 destroy organisms that bring on disease, decay, and dis- 

 agreeable odors. There are several common and effective 

 kinds. In handling disinfectants great care should be exer- 

 cised, as many are very poisonous. 



Lime. Unslaked lime (CaO) and water-slaked lime 

 (Ca(OH)2) are the cheapest and most easily obtained dis- 

 infectants. Air-slaked lime (CaCOs) has no disinfecting 

 properties except that due to absorption. Lime that is to 

 be used for disinfecting purposes should be kept in recep- 

 tacles that are tight enough to exclude air. It is best applied 

 in the form of milk of lime, prepared as follows: Treat 

 a lump of quick-lime in a covered vessel with water until 

 a creamy liquid is formed. This should be kept in an air- 

 tight receptacle when not in use. Quicklime may be pul- 

 verized and sprinkled on dry; this form is especially useful 

 in closets, replacing earth. 



Chlorinated Lime (Bleaching powder, CaClsO). This 

 material is prepared by showering slaked lime powder 

 through chlorine gas. It is a white powder, which decom- 

 poses slowly on exposure to moisture, giving off hypochlorous 

 acid, which is the substance that gives the characteristic 



