'^54' ANALYSIS. 



refcrlptJai and ^^^ ^^^'^a In B, D, and F, = 3^; the oxfde of iron (D.) 



anaiyfisof a =y\;, and lime F, -j2j; the volatile parts of this fubftance 

 mineral from . r •? • ^l j-^ • i j 



Cornwall. = 15| m the 50 grains employed. 



The fum total of thefe is . - « - 47 ^^ 

 Lofs 2H 



50 

 I have fubje6led thefe cryftals, as well as the harder fpeices 

 of this mineral, to analyfis by means of direct folution in 

 fulphuric acid, and have found in each cafe the fame fixed ingre- 

 dients, viz. alumina, a fmall portion of (ihca, and a very minute 

 quantity of lime. Both thefe latter ingredients are, I think, 

 eflfential to thecompofition of this foflil, as I have always dif- 

 covered them in the pureft fpecimens. In this mode of analyfis 

 I experienced the fame difficulty and tedioufnefs of delay in 

 bringing the laft portions of the folution to cryftallize into 

 alum. This anomalous^circumftance I hav« reafon to attribute 

 to a particular combination, which takes place between the 

 fulphate of alumina and lime, filica, and potalh. In my ex- 

 anoination of the compa6l fpecies there was no appearance of 

 the fulphate of lime until the lail ; and in every experiment, 

 previoufly to the fredi appearance of cryftals of alum that 

 had been long delayed, filica and fulphate of lime were dc- 

 pofited. 



I forbear entering into any further details concerning ray 

 former experiments on this curious foffil, as I have reafon to 

 think that it will ftill require a more particular and minute ex- 

 amination, on account of another ingredient which eluded my 

 notice, and which may polTibly imparl to its peculiar character, 

 'X[he fcarcity of it has been hitherto a great bar to my experi- 

 rtents; I ftiall record, hocvever, a few fafts which I have 

 lately obferved, in the hope that at a futare time I may be able 

 to refume my examination of it. 



I was induced to pay more aUention to the volatile ingre- 

 dients of this fubHance *. With this view, I Introduced fome 



* Mr. Humphry Davy, whofe well known ikiH and fagacity 

 have probably rendered the refearches of another perfon fuperflu- 

 ous, had, I found, been engaged in the analyfis of a mineral which 

 is thought to be identical with the fubjeft of thefe obfervations. 

 He informed me that he had obferved a peculiar fmell, and acid 

 properties in the water diftilled from the fubftance which he cxa- 

 ssSncd, 



2 of 



