396 



On the Composition of Zeolite. By James Smithson, Esq. F.R.S. 

 Read February 7, 1811. [Phil. Trans. 1811, p. 171.] 



Although the substance called Natrolite by Mr. Klaproth has lately 

 been found, under a crystalline form, perfectly similar to that of me- 

 sotype, M. Haiiy has not thought himself warranted, from this cir- 

 cumstance, to consider these two bodies as of the same species, on 

 account of the difference of their chemical composition ; because, 

 according to the analysis of M. Vauquelin, there was not observed 

 to be any soda in zeolite, but, on the contrary, a considerable quan- 

 tity of lime, which is not a constituent part of natrolite. 



Mr. Smithson, on the contrary, is inclined to consider them as the 

 same substance, by the agreement of their chemical properties, as 

 well as crystallographical form. Although he had, many years since, 

 found that the zeolite of Staffa contained soda, as has since been ob- 

 served by Dr. Hutton and Dr. Kennedy, he still felt uncertain whether 

 these were of the same kind as those analysed by M. Vauquelin : 

 but having lately received from M. Haiiy a cluster of mesotype in 

 rectangular prisms, terminated by a quadrangular pyramid, Mr. Smith- 

 son took this opportunity of ascertaining whether this substance and 

 natrolite did or did not differ in their composition. The method pur- 

 sued by the author in the analysis of zeolite was first to expose ten 

 grains of it to a strong heat, for the purpose of ascertaining the loss ; 

 and he found it to be '95 grain. An equal quantity was then dissolved 

 in muriatic acid ; and after the solution had been evaporated to dry- 

 ness, the residuum was exposed to a red heat. Water was then 

 poured upon it, and dissolved a portion, which, upon evaporation, 

 was found to be muriate of soda, weighing 3' 15 grains. From the 

 solution of this salt, neither carbonate of ammonia nor oxalic acid 

 occasioned any precipitate ; by which it appeared that this zeolite 

 contained no lime. 



The residuum from which the muriate of soda had been extracted 

 was next digested in muriatic acid, which dissolved a part, but left 

 undissolved a quantity of silica, which, after being made red hot, 

 weighed 4' 9 grains. The muriatic solution was then evaporated to 

 dryness, and exposed to a red heat ; and the residuum appeared to 

 be pure alumina. Since it was possible that some magnesia might 

 also be mixed with it, it was dissolved in sulphuric acid, and ignited; 

 but the residuum was not found to yield any sulphate of magnesia 

 by addition of water to it. The whole of the sulphuric acid, how- 

 ever, had not been expelled by heat, but was afterwards separated 

 by nitrate of barytes ; and the alumina was estimated to amount to 

 2'7 grains. 



The results thus obtained accorded so nearly with the analysis of 

 natrolite, as given by Klaproth, that it was judged unnecessary to 

 repeat his experiments on that substance. 



Mr. Smithson is induced to prefer the name of Natrolite to that of 

 Mesotype, from a desire to preserve unaltered the name given by 

 Baron Cronstadt, the original discoverer of this class of bodice ; and 



