HAIL AND HAILSTONES. 487 



Meanwhile the sulphur, the silica, and other insoluble matter in the gangue 

 will be deposited at the anode. 



Suppose that we operate upon a multiple argentiferous sulphide of lead the 

 ore of which contains also iron, copper, and zinc. It may happen that under 

 the action of an electric current sufficiently energetic the iron and zinc dissolve 

 as rapidly as the other metals, but are not as easily precipitated. In this case 

 the electrolytic solution will become gradually saturated with zinc and iron. It 

 is then advisable to regulate the galvanic current so that the lead, silver gold 

 and copper may be precipitated alone upon the cathode, keeping the zinc dis- 

 solved in the state of zinc nitrate. 



As the bath becomes saturated with zinc nitrate, the iron nitrate yields the 

 precedence, and its base falls to the bottom of the bath in the state of ferric 

 oxide. 



Finally, when the bath is almost entirely saturated with zinc nitrate which 

 is kept in a state non-precipitable by regulating the current accordingly, this solu- 

 tion of zinc is syphoned off for separate treatment. 



The opportunity is taken to remove the metals, copper, lead, silver and 

 gold, which have been thrown down upon the cathode in the metallic state. The 

 ferric oxide at the bottom of the bath is withdrawn separately, and also the sul- 

 phur and the silica found at the anode. 



The method of ulterior purification of the sulphur is given above. 



The metallic zinc contained in the liquid syphoned off may then be precipi- 

 tated by a more powerful current. If it is desired to collect the zinc in the state 

 of oxide it must be precipitated not electrolytically but by means of chemical re- 

 actions. 



This separate zinc-bath is treated first with a little zinc oxide, which throws 

 down any iron present in the state of insoluble oxide. Then, if needful the 

 liquid is placed in a precipitation bath with a zinc plate for anode. A feeble 

 electric current will throw down upon this cathode all the lead, copper, or silver 

 which the bath may retain, leaving merely pure zinc nitrate. — Les Monies. 



METEOROLOGY. 



HAIL AND HAILSTONES. 



FRANCIS E. NIPHER. 



In his work on Tornadoes and Water-spouts Mr. Ferrel, of ''the U. S. Coast 

 Survey, has explained the formation of hailstones in an exceedingly satisfactory 

 manner. According to Mr. Ferrel, the birth-place of hailstones Js in the vortex 

 of the tornado. The tornado is the result of an unstable condition of the air due 



