M. Scheerer's Observations on Elccolith and Nephcline. 115 



Since all the elaeoliths analysed approximate in the quan- 

 tity of foreign constituents to one of these three cases, a com- 

 parison may be easily instituted between the compositions 

 found and the corresponding calculated ones. It will then be 

 seen that none of the analyses approach to the atomic propor- 

 tion of the old formula, with the exception of M. Bromeis' 

 two analyses ; but even these still give ] per cent silica more 

 than is required by the old formula, although M. Bromeis 

 undoubtedly took the greatest precaution not to find too 

 much silica. 



It might still be supposed by those who cling so fast to the 

 sacred number of three in chemical formula?, that some cir- 

 cumstance or other in the mode of analysis pursued by Mr. 

 Francis and myself may have produced the constant supposed 

 overplus of silica; I will therefore give a sketch of the method 

 we employed. The mineral in powder was triturated in an 

 agate mortar, and dried in a water bath, and was then treated 

 with hydrochloric acid, with constant stirring, till the forma- 

 tion of a perfectly gelatinous mass occurred : this was left for 

 some time, usually a day, in a warm place, and then in some 

 analyses evaporated to dryness ; and in others, still contain- 

 ing acid, treated immediately with water. The mass eva- 

 porated to dryness was again moistened with acid, and 

 after an hour water was added to it and it was filtered. The 

 silica, after incandescence and weighing, was tested as to its 

 purity by boiling with carbonate of soda. Small quantities of 

 silica were subsequently separated from the alumina, per- 

 oxide of iron, and the mixture of chloride of potassium, and 

 chloride of sodium, and were added to the chief quantity. 

 With this method there are four points of doubt, in which 

 it is uncertain whether the amount of silica is influenced. 1. 

 It may be questioned whether, when the mass of decomposed 

 mineral, evaporated to dryness, is moistened with hydro- 

 chloric acid, and left to stand in this state for an hour or so, 

 all the hydrochlorate of alumina, which has become basic, is 

 re-dissolved. That this is, however, the case, is evident from 

 there being no perceptible difference in the amount of silica, 

 whether all the acid is expelled or the gelatinous mass, con- 

 taining immediately acid treated with water. 2. On boil- 

 ing the silica which had been heated to redness with a con- 

 centrated solution of carbonate of soda, there was always left 

 an insoluble residue. Two cases must here be distinguished. 

 This residue either consists of light flocks having the appear- 

 ance of silica, or of these and a heavier powder of a sandy na- 

 ture, and which is evidently some foreign mineral not decom- 

 posed by the hydrochloric acid ; it must, therefore, in per- 



12 



