COPPER, ZINC, LEAD, ETC. 149 



of alkaline copper sulfate solution and heat to boiling. Observe 

 the brown precipitate of Cu 2 O. The amount of Cu 2 O produced is 

 proportional to the amount of glucose present and when the work 

 is carefully done and the copper weighed or determined by other 

 means, the percentage amount of glucose in a material can be de- 

 termined. A hot alkaline solution of copper sulfate is reduced to 

 Cu 2 O in the presence of glucose, and a few other organic com- 

 pounds. 



190. Bordeaux Mixture. In this preparation, the 

 copper is present as an insoluble hydroxid. To prepare 

 the Bordeaux mixture 12.5 pounds of copper sulfate 

 are dissolved in about 2 gallons of hot water; 3.5 pounds 

 of lime are slaked in about 2 gallons of water, and 

 strained into a barrel through a coarse cloth to remove 

 any large pieces. The solution of copper sulfate is then 

 poured into the barrel and well stirred. The reaction 

 which takes place is 



Ca(OH) 2 + CuSO 4 = Cu(OH) 2 -f CaSO 4 . 

 In the preparation of Bordeaux mixture, it is the aim 

 to use just a sufficient amount of lime to combine with 

 all of the copper. 



191. Occurrence of Zinc. This metal is found in nature 

 mainly as zinc carbonate, ZnCO 3 , and to a less extent as 

 the sulfid. Small amounts are found in other forms. 

 Zinc is separated from its ores by roasting with char- 

 coal which, volatilizes and it is then collected as zinc 

 dust. It is then purified and prepared for various pur- 

 poses. 



192. Compounds of Zinc. Zinc forms a large number 

 of compounds as ZnCl 2 , Zn(OH) 2 , ZnS, and ZnSO 4 . 



