172 Mr. Smithson on the Composition 
crystalline form, and this form appears to be perfectly similar 
to that of zeolite, but Mr. Hauy has not judged himself war- 
ranted by this circumstance, to consider these two bodies as 
of the same species, because zeolite, he says, “ does not con- 
tain an atom of soda.” * 
I had many years ago found soda in what I considered to 
be zeolites, which I had collected in the island of S afFa, having 
formed Glauber's salt by treating them with sulphuric acid; 
and I have since repeatedly ascertained the presence of the 
same principle in similar stones from various other places ; 
and Dr. Hutton and Dr. Kennedy, had likewise detected 
soda in bodies, to which they gave the name of zeolite. 
There was, however, no certainty that the subjects of any 
of these experiments were of the same nature as what Mr. 
Vauquelin had examined, were of that species which Mr. 
Hauy calls mesotype. 
Mr. Hauy was so obliging as to send me lately, some spe- 
cimens of minerals. There happened to be amongst them a 
cluster of zeolite in rectangular tetrahedral prisms, terminated 
by obtuse tetrahedral pyramids whose faces coincided with those 
of the prism. These crystals were of a considerable size, 
and perfectly homogeneous, and labelled by himself “ Mesotype 
pyramidee du depart, du Puy de Dome.” I availed myself of 
this very favourable opportunity, to ascertain whether the 
mesotype of Mr. Hauy and natrolite, did or did not differ in 
their composition, and the results of the experiments have been 
entirely unfavourable to their separation, as the following 
^account of them will show. 
10 grains of this zeolite being kept red hot for five minutes 
* Journal des Mines, No. CL. Juin 1810, p. 458. 
