293 
Evaporation in Vacuo . 
to the state oi' incandescence whereon you may project a 
j few drops of water : so soon as it is completely filled with 
I steam, turn it quickly with its mouth downward upon a 
, plate or dish whereon you have previously placed two 
! capsules, the one containing concentrated sulphuric acid, 
the other water. There should be a border of wax soften- 
ed with turpentine into which the edge of the inverted 
bell glass should be pressed, to exclude the access of ex- 
ternal air ; and the wax should also be pressed close to 
the edge of the glass. The oil of vitriol will soon absorb 
the vapour, and if the experiment has been neatly con- 
ducted, the other capsule containing water, will exhibit 
the paradoxical appearance of ice formed by the means 
of boiling water. 
The advantage of being thus able to procure ice at all 
seasons and in all situations, may be considered as more 
curious than useful. But a method of operating in the 
large way upon the same principle, without the aid of an 
air pump, and by means of which meat, fish, milk, &c. 
may be dried, the juices of fruits and saline solutions con- 
centrated so as to serve the purposes of general conveni- 
ance, is what I mean to propose. 
I have discovered that steam may be raised by throw- 
ing Welter on ignited substances, and that steam may be 
absorbed by substances proper for the purpose in large 
boxes or chambers. The vacuum thus produced will 
remain a considerable time, provided the boxes are exact- 
ly jointed, made of compact wood, and covered on the 
outside with three or four coats of fat varnish, or amber 
varnish. Nor will the pressure of the atmosphere pass 
through a stone wall, if made of vitrifiable stones (quart- 
zose) or of basalt, cemented by mastic : (that is I presume 
not varnish made of mastic, but any resinous cement.) 
Hence for the purpose of using this new method of desicca- 
tion* cold stoves may be employed, where the subjects will 
