418 | Miscellanies. 
25. Alum in Mica Slate.—This fact is of not unfrequent occur- 
rence in’ this country. A crumbling, half decomposed mica slate, 
now lies before us, containing beautiful incrustations and masses of 
plumose alum in fine silky crystals not unlike those of the Island of 
Milo, (Greece.) We are informed that the rock is found about three 
feet from the surface of the earth, and the alt aa to be es 
the deeper the digging proceeds. 
. Some mica slates contain sufficient sulphur to burn "hod when laid 
on a hot shovel,* or coals, and the alum would appear to be formed 
between the sulphur, becoming sulphuric acid, by the action of the 
oxygen of air or water, or both, and'the alumina of the mica, aided 
ably by alkali in the same mineral. 
f materials of this kind should be found in abundance, they might 
form the basis of a profitable manufacture. 
In the present instance, reference may be had to Mr. Christopher 
_ Johnson, of Colchester, Conn., where the rock is found. 
Fed 
_—_ 
| Addition to Prof. Johnson’s prece on steam.f 
On page 310, after “direct ratio of the density,” fine 7th, insert the 
following :—It i is true that if only one boiler in a range were to be- 
come empty and exposed to excessive heat, at the ‘same time, the 
quantity of steam just calculated, would be, ‘in part, distributed, 
“ through the connecting pipe, to the others, at the moment of its pro- 
: duction, which would diminish in a measure the pressure in the 
~ over | heated boiler. It may be said on the other hand, that the over 
te * ng of the outer shell will never be confined to the lower arch, 
: ‘nor to a single boiler in a range; and it is evident that the lower 
. boilers i m a boat must in the. cases supposed want steam room in pro- 
"portion as the upper want waters and that the connecting pipe could 
_hot, as generally c eae. away the steam so fast as it 
“would be produc ~ The r which had been most remote from 
. the wharf, has generally sustained the i injury, in explosions that have 
+) occurred eee ar putting off. 
“4 4 
aif, hoe 
Ere 
_* In this instance, Be exhales the smell of sulphur, but without flame ; most ‘2 
r has evidently been acidified eed 
5" cs ed too late for insertion in its proper —_— 
a . | 
~ 4 
_ % i * Be . 
or =) ae Bx eae: 
