31 B Mr t Knox's experiments and observations 
Silex . . . 
Alumina 
Lime 
Oxide of iron 
Oxide of manganese . 
Soda 
Water 
• 73 
. 0,10 
• 1 >75 
• 8,50 
i4>5° 
J,00 
1,00 
99$5 
He obtained his silex by exposing 100 grains of the pul- 
verised stone, along with 200 grains of caustic soda, to a 
strong red heat, for half an hour, in a silver crucible ; when 
cool, softening with water, dissolving in muriatic acid, evapo- 
rating nearly to dryness, diffusing in water, and filtering. 
The alumina was obtained by boiling the muriated solution, 
thus freed from silex, with excess of caustic soda. The 
alumina was held in solution while the lime and iron were 
thrown down. The alkali was then neutralised, and the earth 
precipitated by carbonate of soda. The precipitated lime and 
iron, first dissolved in muriatic acid, and then combined with 
sulphuric acid, gave sulphate of lime, which was collected and 
washed with weak spirits of wine, and the pure lime was 
estimated as in the proportion of one to three in the sul- 
phate. 
The iron was precipitated by carbonate of ammonia. Some 
flocks, which appeared in the remaining fluid after it had been 
evaporated to dryness and re-dissolved, were presumed to be 
manganese, and estimated at one-tenth of a grain. 
I proceeded in the same manner but obtained no manga- 
