94 Dr. Thomas Thomson on the [Feb. 



neutral as possible, and then digested with benzoic acid for 

 about half an hour. The whole was then passed through a 

 weighed filter. The liquid that passed through the filter 

 was colourless ; the iron in the state of benzoate was retained 

 on the filter. Benzoic acid was used instead of benzoate of 

 ammonia, because I knew from previous experiments that 

 benzoate of ammonia throws down cerium as well as iron, 

 which is not the case with benzoic acid. The benzoate of 

 iron left on the filter was washed with a solution of sal- 

 ammoniac till every thing soluble was taken up. Had I 

 washed it with water, as it contained an excess of acid, the 

 greater part of the benzoate of iron would have re-dissolved. 

 The benzoate of iron being dried and ignited left 1*09 grains 

 peroxide of iron. 



5. The colourless liquid thus freed from iron, was preci- 

 pitated by ammonia, and the precipitate collected upon a 

 weighed filter. It was a white transparent jelly, which 

 took a very long time to wash it properly ; but it gradually 

 acquired colour by exposure to the air ; and after being 

 dried and ignited in an open vessel it was red. It was 

 peroxide of cerium, and weighed 5*19 grains = 4*813 grains 

 of protoxide of cerium. 



6. The liquid thus freed from cerium was precipitated 

 hot by oxalate of ammonia, and the precipitate was collected 

 on a weighed filter, washed, dried, and ignited; it amounted 

 to 4*48 grains, and was carbonate of lime = 2*5 grains 

 lime. 



7. Nothing else could be found in the liquid when treated 

 with carbonate of ammonia. 



The constituents thus found are 



Moisture 0-31 or 1-55 



Silica 9-22 „ 46-10 



Peroxide of iron - - - - 1*09 ,, 5*45 



Protoxide of cerium - - - 5*19 ,, 25*95 



Lime 2*50 „ 12*50 



18*31 91*55 



The loss of 8*45 per cent, rendered it probable that the 

 mineral contained an alkali. To determine this point, 28 

 grains of it in fine powder, were intimately mixed with 50 

 grains of litharge and 25 grains of nitrate of lead, and fused 



