BASIC COPPER SULFATE AS A FUNGICIDE 127 



The sodium carbonate mix is the most difficult of the three to control but the 

 color and reaction are fairly safe guides. The batch yields about 3 pounds of 

 material. 



Composition of Laboratory Samples 



The analyses of two samples of basic copper sulfate prepared in the Station 

 laboratory with an excess of calcium carbonate have been published (6, p. 747) 

 but are again reported with a new hypothetical combination based on the theory 

 of tribasic sulfate with the excess as copper hydroxide, which may or may not be 

 more accurate. The theoretical composition, however, was merely incidental to 

 the project and not pursued at length. 



Basic Copper Sulfate 



Sample No. 1 Sample No. 2 



Per cent Per cent 



Water, 100°C 7.880 8.900 



Cupric oxide, CuO 32.732 32.356 



Copper, Cu (26.150) (25.850) 



Calcium oxide, CaO 17.750 17.770 



Carbon dioxide, CO, 0.803 0.805 



Sulfur trioxide, SO3 30.930 30.790 



Hypothetical Combination 



Tribasic sulfate, 4CuO.S03.4H„0 41.39 40.43 



Copper hydroxide, Cu(OH)a 6.39 6.76 



Calcium sulfate, CaSO'^.2H5,0 51.36 51.41 



Calcium carbonate, CaCOj 1.83 1.83 



As some of the hydrated compounds present were apparently unstable, the 

 hygroscopic moisture determined is of little value and this may also account for 

 the overrun in the calculations. 



Another sample prepared with an excess of basic magnesium carbonate had the 

 following composition: 



Basic Copper Sulfate 



Per cent 



Water, 103°C 0.694 



Cupric oxide, CuO 67.316 



Copper, Cu (53.780) 



Ferric oxide, FeoOj 0.025 



Magnesium oxide, MgO 0.400 



Carbon dioxide, CO, 0.939 



Sulfur trioxide, SO3 16.180 



Hypothetical Combination 



Tribasic sulfate, 4CuO.SO3.4HjO 95.06 



Copper hydroxide, Cu(OH)2 1.06 



Copper carbonate, CuC03.Cu(0H)2 2.97 



Ferric hydroxide, Fe(OH) 3 0.04 



Basic magnesium carbonate, 4MgCo3.Mg(OH)2.5HjO 0.96 



The product obtained with magnesium carbonate is more highly concentrated, 

 as the magnesium sulfate is removed by washing, and tends to confirm the hypoth- 

 esis as to formation of a tribasic salt. 



Basic copper sulfate prepared with different carbonates varies somewhat in 

 color, from batch to batch, but as a rule a greenish-blue to a light blue precipitate 

 is preferable to a deeper colored product. After sieving, a good quality basic 

 sulfate made from calcium carbonate should have a volume of 5 to 6 cubic centi- 

 meters to the gram ; from magnesium carbonate, of about 3 c.c. ; and from sodium 

 carbonate, of about 2 c.c. 



