2 Sr 
34 On the Efjcéls produced on different Stones 
hours in the ftove-heat, remained unchanged, and had fuf> 
tained no lofs of its weight or its {plendour. 
That I might not leave magnefian {tone unexamined, I 
expofed, for forty -eight hours, at the ftove-heat, a thin plate 
of Venetian tale w cighing 124 grains. After the experiment 
it weighed only 81 grains, and had therefore decreafed in 
weight more than }: it had alfo fallen into a foft tender 
powder, which floated on water, and had the appearance of 
magnefia. I poured water on the refiduum in the appa- 
ratus, and found next day the fides incrufted with {mall 
cryftalline glittering flakes, adhering in detached maffes, 
which could not be wafhed of with diluted nitrous acid. 
Though thefe may ! have been real magnefian falt, they feem, 
‘however, to throw fome light on the cryttallifation of ftones. 
Bergman had before ae ed the filiceous cryftallifation 
formed in diluted fluor acid, which had ftood a long time 
at reft over powder of filex. 
Among the various hypothefes refpeéting the formation of 
granite, and ftones in general, that which fuppofes the an- 
cient ocean, fo much fool of by modern geologues, to 
have confifted of a fluid totally different from that of our 
fea-water, and of which the latter may be only the refiduum, 
is not the moft improbable. In my experiments, about 50 
grains of the powder of fparry fluor, mixed with as much 
concentrated fulphurous acid as was equal to the fpace oc- 
gupied by the powder, was put into a tin-plate box, and the 
latter into another of the content of about 20 fquare inches ; 
to the lid of which, of firong tin-plate, I fattened, with wax, 
he fpecimens to be tried, Pad fhut the whole fo as to be 
‘air-ti ight. After expofing various kinds of ftones for fourteen 
days i found the inner {mall veffel in part corroded, and on 
the exterior fides a moift, weakly-adhering falt, cryftallifed 
in a confiderable quantity, which at firtt | confidered as a 
mixture of iron and fluo-fulphat ef lead, tin being feldom 
worked pure, and the folder having begun to give way. It 
is, however, poflible that fome tin may have been diffolved 
by the two acids combined. I diffolved fome of this vitriol 
in diftilled water, and dropped into it fome fpiritous tinCture 
of galls. The liquor became of a beautiful indigo-blue co- 
jours inftead of black or purple as I expected; “and a very 
light 
