108 GALVANIC ELECTRICITY. 



259. Before combining the battery as 



How and why ...... 



is the zinc above described, it is best to wash the 



zinc with soa P and water > and afterward 

 with dilute sulphuric acid, and then to 

 immerse it for half a minute or so in a solution of ni- 

 trate of mercury. By this process, the zinc acquires 

 a thin film of quicksilver, which afterward protects it 

 from the action of the acid used to excite the battery, 

 excepting when the current is completed. When the 

 battery is in operation, it also has the effect of making 

 the action, more equal and constant. It is then to 

 be again washed, and newly immersed in the acid solu- 

 tion. This solution is prepared by dissolving quicksil- 

 ver, of the bulk of two peas, in nitric acid, and pouring 

 the clear liquid into a tumbler of water. 



260. THE EXCITING ACID. The exci- 



How is the ex- . . 



citing acid ting liquid is dilute sulphuric acid, consist- 

 preparc . .^ ^ Qne p art Q .J ^ vitriol, to ten parts of 



water. The acid is poured into the proper quantity of 

 water, and set aside to cool. 



261. THE SILVERING SOLUTION. To 



How is the sil- . . 



vering solution make a half pint of the solution, a dime is 

 prepared? placed in a test-tube and dissolved in ni- 

 tric acid, the solution being diluted with water. Muri- 

 atic acid is then added, which precipitates the silver, in 

 the form of a white curd. This is allowed to settle, and 

 the green liquid, which contains the copper of the coin, 

 is poured off. Water is again added, and the curd al- 

 lowed to settle ; this cleansing process is several 

 times repeated. The test-tube is then half filled with 

 water, and heated, and bits of cyanide of potassium ad- 

 ded, until a transparent solution is obtained. 



