158 



PRACTICAL PHYSIOLOGY. 



[xxv. 



2, Wilke's Pole-Reagent Paper. — This is a convenient method for deter- 

 mining the ( - ) pole in any combination. Moisten one of the papers, place it 

 on a clean piece of glass, and touch the surface with the two wires coming 

 from the battery ; a red spot indicates the negative pole. 



3. Amalgamation of the Zinc. — (a.) The zinc should always 

 be weU amalgamated. When a cell hisses the zinc requires to 

 be amalgamated. Dip the zinc in lo p.c. sulphuric acid until 

 effervescence commences. Lift it out and place it on a shallow 

 porcelain plate. Pour some mercury on the zinc, and with a 

 piece of cloth rub the mercury well over the zinc. Dip the zinc 

 in the acid again, and then scrub the surface with a rag under a 

 stream of water from the tap. CoUect all the surplus mercury 

 and place it in the bottle labelled "Amalgamation Mixture." 

 Take care that none of the mercury gets into the soil-pipe. A 



very convenient method is to 

 dip the zinc into a thick-walled 

 glass tube containing mercury 

 and sulphuric acid. For con- 

 venience the tube is fixed in a 

 block of wood. 



(b.) The following is another con- 

 venient * ' Amalgamation Mixture " : 

 — Witli the aid of gentle heat dissolve 

 4 parts of mercury in 5 parts of 

 nitric acid and 15 parts of hydro- 

 chloric acid, and then add 20 parts 

 of hydrochloric acid. The zincs, after 

 being well cleaned, as directed above, 

 are dipped into this mixture, or the 

 mixture may be applied to the clean 

 zinc by means of a brush. 



N.B. — After using a battery 

 the zincs must be washed and 

 dried, the porous cells must 

 be carefully washed, and com- 

 ^■'"'i'Jlir pletely immersed in a large 

 Yi ; -]'-n It quantity of water, frequently 



renewed. 



4. Grove's Cell (fig. 81) consists of an outer glazed earthenware, 

 glass, or ebonite jar, containing amalgamated zinc and 10 p.c. 

 sulphuric acid. In the inner porous cell is placed platinum foil 

 witii strong nitric acid. The ])lafcinum is the + positive pole or 

 anode, the zinc the - negative pole or cathode. For physiological 

 purposes, the small Grove's cells, about 7 cm. in diameter and 5 cm. 

 in height, are very convenient. When in use the battery ought to 



