Chemistry... | 257 
___-» With distilled water free from air, the same phenomenon was ob- 
____ served, and by a series of comparative experiments the author is led to 
believe that cohesion alone can sustain a column of water over 33 feet. 
at It is the absence of air alone that allows the particles of liquids to ap- 
____ proach each other more closely, and exercise more powerfully their 
cohesion, which, when air is present, interferes but slightly with 
the changes that liquids undergo, as for instance ebullition, that happens 
_ at about the temperature at which their vapors enter into equilibrium 
_____ with the atmospheric pressure. But if water is as free from air as it is 
_— possible to make it, it can be heated to the temperature 275° Fahr. with- 
_ -—s- Qué - manifesting the slightest traces of ebullition, and that, even in a 
i + Vacuum ;—this remarkable fact has been proved by experiment, the in- 
’ 
i 
eat Strument used for it being a kind of water hammer,—so arranged that the 
Vapor in the upper part could not be heated, and thereby exercise a pres- 
Sure upon the water,—which was heated to 275° Fahr. without the ad- 
hesion of the particles giving way ; showing that this force was superior 
to the pressure of three atmospheres, as under ordinary circumstances, 
Water; heated to 275°, furnishes a vapor equal to that pressure. 
_ But if the water heated to this high temperature be divided in any 
Way, steam is disengaged instantly and with great violence, the temper- 
ature at the same time falling. In this way those sudden bursts of va- 
Per, which are often so annoying during the evaporation of liquids, are - 
{| _—s* plained. At the first part of the ebullition while air is present the 
___ Yapor is uniformly produced, the temperature of water and vapor being 
: the same ; but the air once gone, the cohesion of the liquid interferes in 
‘the process ; this induced the author to try what effect a current of air 
ae Passing through the liquid would have in preventing these explosions, 
ee Which resulted in perfect success. 
- M. Donny thinks that the cause of certain explosion of boilers, may 
et be deduced from these facts, and proposes as a means of preventing 
_ them, to throw in at the bottom of the boiler a small stream of air. 
: é experiments have an important bearing upon the point of ebulli- 
_ Hon of liquids. It is impossible to enter more into detail concerning 
these interesting researches, which extend over more than twenty pages, 
: wut which recommend themselves to the perusal of ancien me ‘we 
ae 
— Bral as . : : . 
| 6A New Method for the Quantitative Determination of Iron ; by 
= WisicetbientConstc Rendus, April, 1846.)—This method is based 
sted the fact, that when a solution of the permanganate of potash—the 
Chameleon mineral—is added to a solution of the protoxide of iron, the 
ak ~~ t is discolored so long as any of the latter metal remains in the 
“State of protoxide.. With this in view the author proceeds as follows. 
* Dissolve the ore. in hydrochloric acid. 2. Convert the persalt of 
* 
