34*0 Mr. Gregor’s Experiments on a mineral Substance 
sulphuric acid, and have found in each case the same fixed ingre- 
dients, viz. alumina, a small portion of silica, and a very minute 
quantity of lime. Both these latter ingredients are, I think, 
essential to the composition of this fossil, as I have always dis- 
covered them in the purest specimens. In this mode of analysis 
f experienced the same difficulty and tediousness of delay in 
bringing the last portions of the solution to crystallize into 
alum. This anomalous circumstance I have reason to attribute 
to a particular combination, which takes place between the 
sulphat of alumina and lime, silica, and potash. In my exami- 
nation of the compact species there was no appearance of the 
sulphat of lime until the last ; and in every experiment, previ- 
ously to the fresh appearance of crystals of alum, that had 
been long delayed, silica and sulphat of lime were deposited. 
I forbear entering into any further details concerning my 
former experiments on this curious fossil, as I have reason to 
think that it will still require a more particular and minute ex- 
amination, on account of another ingredient which eluded my 
notice, and which may possibly impart to it its peculiar character. 
The scarcity of it has been hitherto a great bar to my experi- 
ments ; I shall record, however, a few facts which I have 
lately observed, in the hope that at a future time I may be able 
to resume my examination of it. 
I was induced to pay more attention to the volatile ingre- 
dients of this substance.* With this view, I introduced some 
of the crystals into a small retort, adapted a receiver unto it, 
* Mr. Humphry Davy, whose well known skill and sagacity have probably ren- 
dered the researches of another person superfluous, had, I found, been engaged in the 
analysis of a mineral which is thought to be identical with the subject of these obser- 
vations. He informed me that he had observed a peculiar smell, and acid properties 
in the water distilled from the substance which he examined. 
