749 
grecs that it had lost before constitute 140°, or 
the whole of the caloric necessary to keep it 
fluid, assumes of consequence the form of 
ice. 
Fourth. If these experiments should not be 
considered as sufficient tc warrant Dr Black’s 
conclusion, the following, for which we are 
indebted to the same philosopher, puts the 
truth of his opinion beyond the reach of dis- 
pute. He mixed together given weights of 
ice at 32°, and water at 190° of temperature. 
The ice was melted in a few seconds, and the 
temperature produced was 53°. 
The weight of the ice was 1 19 half-drachms ; 
That of the hot water 135 
of the mixture 25 4 
of the glass vessel Id 
Sixteen parts of glass have the same effect in 
heating cold bodies, as eight parts of equally 
hot water. Therefore, instead of the Id halt- 
drachms of glass, eight of water may be sub- 
stituted, which makes the hot water amount 
to 143 half-drachms. 
In this experiment there were 158 degrees 
of heat contained in the hot water, to be di- 
vided between the ice and the water. H ad 
they been divided equally, and had the whole 
been afterwards sensible to the thermometer, 
the water would have retained ■§■£§• parts of 
this heat, and the ice would have received 
XtSL parts : that is to say, the water would 
have retained 86°, and the ice would have 
received 72°; and the temperature after mix- 
ture would have been 104°, But the tempe- 
rature by experiment is found to be only 53°; 
the hot water lost 137°, and the ice only re- 
ceived an addition of temperature equal to 
21°. But the loss of 18° of temperature in 
the water is equivalent to the gain of 21° in 
the ice. 1 herefore 158° — 18° 140 of heat 
have disappeared altogether from the hot wa- 
ter, These 140° must have entered into the 
ice, and converted it into water without rais- 
ing its temperature. 
In the same manner, if we take any quan- 
tity of ice, or, which is the same thing, snow 
at 32°, and mix it with an equal weight, of 
water at 172°, the snow instantly melts, and 
the temperature of the mixture is only 32°. 
Here the water is cooled 140°, while the tem- 
perature of the snow is not increased at all; 
so that 140° of caloric have disappeared. 
They must have combined with the snow; 
but they have only melted it, without in- 
creasing its temperature. Hence it follows 
irresistibly, that ice, when it is converted 
into water, absorbs and combines with 140° 
of caloric. 
Water, then, after being cooled down to 
32°, cannot freeze till it has parted with 140° 
of caloric ; and ice, after being heated to 32°, 
cannot melt till it has absorbed 140° of ca- 
loric. This is the cause of the extreme 
slowness of these operations. With regard 
to water, then, there can be no doubt that 
it owes its fluidity to the caloric which it con- 
tains, and that the caloric necessary to give 
fluidity to ice is equal to 14.0 s . 
To the quantity of caloric which thus occa- 
sions the fluidity of solid bodies by combining 
with them. Dr. Black gave the name of la- 
tent heat, because its presence is not indi- 
cated by the thermometer; a term, suffi- 
ciently expressive, but other philosophers 
have rather chosen to call it. caloric of flui- 
dity*. 
FLUIDITY, 
Dr. Black and his friends ascertained also, 
by experiment, that the fluidity of melted wax, 
tallow, spermaceti, and metals, is owing to 
the same cause- JLandriani proved, that this 
is the case with sulphur, alum, nitre, and se- 
veral of the metals; and it has been found to 
be the case with every substance hitherto 
examined. We may consider it thereto! e as 
a general law, that whenever a solid is con- 
verted into a fluid, it combines with caloric, 
and that this is the cause of its fluidity. 
From the experiments of I)r. Irvine, it ap- 
pears that the caloric of fluidity of sperma- 
ceti is 1 45° 
Bees-wax 175 
Tin 500. 
These are the only substances in which the 
quantity of caloric, absorbed during fusion, 
has been ascertained. In all ot them we see 
this rule to hold, that the caloric of fluidity 
increases with the temperature at which liqui- 
dity takes place. 
Dr. Black lias rendered it exceedingly 
probable also, or rather he has proved by his 
experiments and observations, that the soft- 
ness of such bodies as are rendered plastic by 
heat, depends upon a quantity of latent heat 
which combines with them. Metals also owe 
their malleability and ductility to the same 
cause. Hence the reason why they become 
hot and brittle when hammered. 
II. Thus it appears, that the conversion of 
solids into liquids, is occasioned by the com- 
bination of a dose of caloric with the solid. 
But there is another change of state still more 
remarkable, to which bodies are liable when 
exposed to the action of heat. Almost all 
liquids, when raised to a certain temperature, 
gradually assume the form of an elastic fluid, 
invisible like air, and possessed of the same 
mechanical properties. Thus water, by 
boiling, is converted into steam, an invisible 
fluid, 1800 times more bulky than water, and 
as elastic as air. T hese fluids retain their 
elastic form as long as their temperature re- 
mains sufficiently high; but when cooled 
down again, they lose that form, and are con- 
verted into liquids. All liquids, and even a 
considerable number of solids, are capable of 
undergoing this change when sufficiently 
heated. 
With respect to tire temperatures at which 
liquids undergo this change, they may be all 
arranged under two divisions. T here are 
some liquids which are gradually' converted 
into elastic fluids at every temperature, while 
others again never begin to assume that 
change till their temperature reaches a cer- 
tain point. Water is a well-known example 
of the first class of bodies. If an open vessel, 
filled with water, is carefully examined, we 
find that the water diminishes in bulk day 
after day, and at last disappears altogether. 
If the experiment is made in a vessel suffi- 
ciently large, and previously exhausted of 
air, we shall find that the water will fill the 
vessel in the state of invisible vapour, in what- 
ever temperature it is placed.. Alcohol like- 
wise, and ether, and volatile oils, gradually 
assume the form of an elastic fluid in all tem- 
peratures. But sulphuric acid and the fixed 
oils never begin to assume the form of va- 
pour till they are raised to a certain tempera- 
ture. Though left in open vessels they lose 
no perceptible weight; neither does sulphuric 
acid lose any weight, though kept ever so 
long in the temperature ot boiling water. 
When liquids gradually assume the form of 
elastic fluids in all temperatures, they are 
said to evaporate spontaneously. The se- 
cond class of liquids want that property' alto- 
gether. 
When all other circumstances are the same, 
the evaporation of liquids increases with their 
temperature ; and after they are heated to a 
certain temperature, they assume the form 
of elastic fluids with great rapidity . If the 
heat is. applied to the bottom of the vessel 
containing the liquids, as is usually the case, 
after the whole liquid has acquired this tem- 
perature, those particles of it which are next 
the bottom become an elastic fluid first: 
they rise up, as they are formed, through the 
liquid, like air-bubbles, and throw the whole 
into violent agitation. The liquid is then 
said to boil. Every particular liquid has a 
fixed point at which this boiling commences 
(other things being the same), and this is 
called the boiling point of the liquid. Thus 
water begins to boil when raised to 212°. It 
is remarkable, that after a liquid has begun to 
boil, it never becomes any hotter, however 
strong the fire to which it is exposed. A 
strong heat indeed makes, it boil more ra- 
pidly, but does not increase its temperature. 
This was first observed by Dr. Hooke. See 
Boiling. 
It was observed, when treating of the melt- 
ing point of solids, that it is capable of being 
varied considerably by altering the situation 
of the body. Thus water may be cooled 
down considerably lower than 32 s , without 
freezing. The boiling point is still less fix- 
ed, depending entirely on the degree of pres- 
sure to which the liquid to be boiled is ex- 
posed. If we diminish the pressure, the 
liquid boils at a lower temperature; if we 
increase it, a higher temperature is necessary 
to produce ebullition. From the experiments 
of professor Robison, it appears that, in a 
vacuum, all liquids boil about 145° lower 
than in the open air under a pressure of 30 
inches of mercury; therefore water would 
boil in vacuo at 67°, and alcohol at 34°. In 
a Papin’s digester, the temperature of water 
may be raised to 300°, or even 400°, without 
ebullition : but the instant that this great pres- 
sure is removed, the boiling commences with 
prodigious violence. 
The elasticity of all the elastic fluids into 
which liquids are converted by heat, in- 
creases with the temperature; and the va- 
pour formed, when the liquid boils in the 
open air, possesses an elasticity just equal to 
that of air, or capable at a medium of balan- 
cing a column of mercury 30 inches high. 
The following very important table, drawn.. 
up by Mr. Dalton from his own experiments, 
exhibits the elasticity of steam, or the vapour 
of water of every temperature, from — 40° to- 
325°. The elasticities of all the temperatures, 
from 32° to 212° were ascertained by experi- 
ment; the rest were calculated by observing, 
the rate at which the elasticity increased os 
diminished according to the temperature. 
