LEA D COPPERBISMUTH. 325 



solves to a deep blue solution, which is essentially Fehling's solution (see Index). 

 The copper enters the negative tartaric acid radical or ion, and while in the 

 cupric state is not precipitated by alkali. If the copper is reduced to the 

 cuprous state, it can no longer remain in solution and is precipitated as the 

 reddish cuprous oxide, Cu 2 O. 



Heat the blue solution to boiling and add a little dilute glucose solution and 

 heat again a few minutes. A precipitate of cuprous oxide is produced, due to 

 the reducing action of the glucose. This is usually employed as a test for 

 glucose in urine. 



Cupric sulphate, Cupri sulphas, CuSO 4 .5HO 2 = 247.85 (Sul- 

 phate of copper, Slue vitriol, Blue-stone). This is the most important 

 compound of copper. It is manufactured on a large scale, either 

 from copper pyrites, or by dissolving cupric oxide in sulphuric acid, 

 evaporating and crystallizing the solution. 



Cupric sulphate forms large, transparent, deep-blue crystals, which 

 are easily soluble in water, and have a nauseous, metallic taste. By 

 heating it to about 200 C. (392 F.) all water of crystallization is 

 expelled, and the anhydrous cupric sulphate formed, which is a white 

 powder. By further heating this is decomposed, sulphuric and 

 sulphurous oxides are evolved, and cupric oxide is left. 



Experiment 41. Boil about 5 grammes of fine copper wire with 15 c.c. of 

 concentrated sulphuric acid until the action ceases and most of the copper 

 is dissolved. Dilute with about 15 c.c. of hot water, filter, and set aside for 

 crystallization State the exact quantities of copper and H 2 S0 4 required to 

 make 100 pounds of crystallized cupric sulphate. 



Cupric carbonate is obtained by the addition of sodium carbonate 

 to solution of cupric sulphate, when a bluish-green precipitate is 

 formed, which is cupric carbonate with hydroxide (Plate III., 4); by 

 dissolving this in the various acids, the different cupric salts are 

 obtained. 



Ammoniocopper compounds. A number of compounds are 

 known which are either double salts of ammonia and copper, or are 

 derived from ammonium salts and contain copper. Thus, cupric 

 chloride forms with ammonia the compounds : CuCl 2 (NH 3 ) 2 , CuCl 2 

 (NH 3 ) 4 , and CuCl 2 (NH 3 ) 6 . Cupric sulphate forms in like manner, 

 cupric- diammonium sulphate, CuSO 4 (NH 3 ) 2 , and cupric tetrammo- 

 nium sulphate, CuSO 4 (NH 3 ) 4 , which is a deep azure-blue compound 

 taking up one molecule of water during crystallization. 



It is this formation of soluble ammonio-copper compounds which 

 causes the deep blue color in solutions of cupric salts on the addition 

 of ammonia water. 



