23 



At all events, the above analyses show that unburnt clay con- 

 tains ammonia, or the elements from which ammonia is formed, in 

 larger quantities than burnt clay. For that reason I cannot 

 attach much value to the ammonia theory. 



9. Does over-burnt clay absorb any or no ammonia from the 

 atmosphere ? 



Sprengel, as has been mentioned before, thinks that in over- 

 burnt clay no ammonia can be produced. The following experi- 

 ment will show with what amount of confidence this doctrine is to 

 be accepted. 



A portion of over-burnt clay from Huntstile, the solubility of 

 which, as proved by the above analysis, was considerably smaller 

 than that of properly burnt (day, was exposed to the atmosphere, 

 moistened with water, for two months and thirteen days. The 

 amount of ammonia was then determined in the same manner as 

 in the preceding experiment. 



219 grs. of air-dry gave 0*155 grs. of bichloride of platinum and 

 ammonium, or 



100 parts furnished only 0-008 per cent of ammonium. 



We thus find that Sprengel's theory is not borne out by 

 direct experiment ; but, at the same time, we see here that the 

 power of absorbing ammonia in over-burnt clay is considerably 

 reduced. 



Moderately burnt clay will absorb double the quantity of 

 ammonia from the atmosphere which will be absorbed by over- 

 burnt clay under precisely the same circumstances. 



10. Is ammonia found in burnt clay containing protoxide of 

 iron, when exposed in a moist state to the atmosphere, in much 

 larger quantities than in the same clay exposed in a dry state to 

 the atmosphere ? 



In answer to this question, the following experiments were 

 instituted : 



A portion of the same clay used throughout in all the experi- 

 ments was moderately burnt in a closed crucible, after having 

 been previously mixed with 1 per cent of charcoal powder. The 

 charcoal powder was mixed with the clay for the purpose of 

 reducing the peroxide of iron in the clay to protoxide. 



(1.) One-half of the clay thus treated was exposed for two 

 months and fourteen days to a dry atmosphere, in a dry state. 



(2.) The other half was thoroughly moistened with water, and 

 exposed for the same length of time to the same atmosphere. 



The quantity of ammonia in each sample was then determined 

 separately. 



(1.) Clay exposed to the atmosphere in a dry state : 182'81 

 grs. gave 0*28 grs. of bichloride of platin. and ammonium, or 

 100 grs. gave 0'17 per cent of ammonium. 

 (2.) Clay exposed to the atmosphere in a wet state: 212-1 1 



