OF THE SEVEN WELLS. 



113 



Alkali or Carbonate of Soda, and are boiled: during 

 the boiling the mixed Oxides unite and form the black 

 Magnetic Oxide. ^3 ° - To form the Magnetic Oxide 5' 

 the processes are precisely similar, in all details, except that 

 only half the quantity, instead of two-thirds (as in the first 

 case), is peroxidised by boiling with Nitric acid. 



After the details above given, it does not seem necessary 

 to enter further into the question of whether the artificial 

 Magnetic Oxides can be obtained so readily and economi- 

 cally as to render their use practicable on the large scale, 

 as any process involving accurate weighing, solution, accu- 

 rate division by graduated measures, boiling and precipita- 

 tion, besides some expenditure for re-agents, would be in- 

 applicable. 



The process has, however, been made available for the 

 manufacture of a sufficient portion of artificial magnetic 

 oxide, to test its efficacy as a filtering and purifying agent. 



The same water in the same quantity was used in each of 

 thft experiments recorded in the Table of Results marked Y. 



Table Y. 



The water selected for the following trials was notorious- 

 ly bad. It was taken from a Well in the compound of the 

 Madras Medical College. The quantity experimented on 

 was the 16th of an Imperial Gallon, 



Previous to any filtration s, one-sixteenth of a gallon was 

 evaporated to dryness, first on a porcelain dish and finally 

 in a Platinum capsule of known weight. It left a total 

 amount of residue— grains 15 "08, and after ignition (with the 

 usual precautions) grains 12*52, which was taken as the 

 inorganic impurity present, and the loss, grains 2*56, as the 

 organic. Nine separate sixteenths of a gallon of the same 

 water, were then carefully filtered through the materials 



