174 Mr. Smithson on the Composition 
To discover whether any magnesia was contained amongst 
this alumina, it was dissolved in sulphuric acid, the solution 
evaporated to a dry state, and ignited. Water did extract 
some saline matter from this ignited alumina, but it had not 
at all the appearance of sulphate of magnesia, and proved to 
be some sulphate of alumina which had escaped decomposition, 
for on an addition of sulphate of ammonia to it. it produced 
crystals of compound sulphate of alumina and ammonia, in 
regular octahedrons. 
This alum and alumina were again mixed and digested in 
ammonia, and the whole dried and made red hot. The alumina 
left, weighed 3.1 grains. 
Being suspected to contain still some sulphuric acid, this 
alumina was dissolved in nitric acid, and an excess of acetate 
of barytes added. A precipitate of sulphate of barytes fell, 
which after being edulcorated and made red hot, weighed 1.2 
grains. If we admit -§• of sulphate of barytes to be sulphuric 
acid, the quantity of the alumina will be =3.1 — 0.4 = 2.7 
grains. 
From the experiments of Dr. Marcet,* it appears that 
3.15 grains of muriate of soda, afford 1.7 grains of soda. 
Hence, according to the foregoing experiments, the 10 grains 
of zeolite analysed, consisted of 
Silica 
4.90 
Alumina 
2.70 
Soda 
1.70 
Ice 
0.95 
10.25 
Phil. Trans. 1807. 
