TREATMENT OF BATTERY. 665 



The snlplmric acid mnst be diluted in the manner explained on 

 page 224. After the porons cell is placed inside the onter vessel, this 

 is filled to about 2 or 3 cm from the top with the dilute acid, pouring 

 it in through a funnel, and holding the porous cell in its place by 

 pressing the finger upon it, or otherwise the cell will float, and it 

 is impossible to see whether the proper quantity of acid has been 

 poured into the outer vessel. The porous cell is then filled with 

 crude concentrated nitric acid, also using a funnel for the purpose ; 

 in Grove's element this is done before the platinum strip is intro- 

 duced, but in Bunsen's the carbon, already provided with its 

 binding screw, is first placed in the cell, and the nitric acid poured 

 in afterwards. The end of the funnel should be held close to the 

 edge of the vessel for a short time before it is removed, so as to 

 avoid dropping any of the nitric acid upon the zinc, binding screws, 

 connecting wires and copper strips, or into the dilute sulphuric 

 acid. The metal parts just mentioned are all strongly attacked by 

 nitric acid, and the dilute sulphuric acid, when it contains an 

 admixture of nitric acid, acts destructively upon the amalgam. If 

 nitric acid should accidentally have dropped upon any of the 

 metallic parts, it should be washed off immediately with water, and 

 the surface of the metal cleaned and dried ; the dilute sulphuric 

 acid into which any of the nitric may have dropped must be taken 

 out. 



The sulphuric acid may be constantly used during several hours 

 for the maintenance of a galvanic current ; but as the circuit is 

 generally closed only a small portion of the time during which the 

 battery is in use, the same acid will serve for a considerable time. 

 After taking the elements to pieces the sulphuric acid may be left 

 in the vessels in which it was, provided these are placed so that 

 they cannot be upset. As soon as crystals (of zinc sulphate) begin 

 to be deposited, the acid ceases to be of further use for the purposes 

 of the battery, and must be poured out of the vessels. 



The nitric acid is at first nearly colourless, but it gradually 

 assumes a yellow colour by being used in the porous cell ; this 

 colour changes afterwards to a bluish-green, and finally the acid 

 again becomes nearly as clear as water. When this disappearance 

 of colour takes place the current becomes greatly enfeebled, and 

 the nitric acid should be changed. 



While the elements are in use red nitrous fumes are constantly 

 evolved, especially after a time when the nitric acid is no longer 

 very new. These vapours are suffocating, and attack metallic parts 

 with which they come into contact. The battery should there- 

 fore not be placed within the room, but if possible upon the 



