dity to liquidity takes place, receive different 
names according to the usual state of the 
body thus changed. W hen the body is usu- 
ally observed in a liquid state, we call the 
temperature at which it assumes the form of 
a solid, its freezing point, or congealin'* 
point, thus tlie temperature in which water 
becomes ice, is called tire freezing point of 
water ; on the other hand, when the body is 
usually in the state of a solid, we call the tem- 
perature at which it liquifies its melting 
point: thus 212° is the melting point of sul- 
phur, 442° the melting point of tin. 
1 lie following table contains a list of the 
melting points of a considerable number of 
solid bodies. 
Melting point. 
594° 
- 576 
442 
- 212 
142 
133 
- 100 
- 92 
50 
36 
32 
30 
23 
20 
14 
36 
39 
46 
46 
66 . 
Substance. 
Lead 
Bismuth 
Tin 
Sulphur 
Wax 
Spermaceti 
Phosphorus 
Tallow 
Oil of anise 
Olive-oil - 
]ce 
Milk - 
Vinegar 
Blood 
Oil of bergamot 
Wines 
Oil of turpentine 
Sulphuric acid 
Mercury 
Liquid ammonia 
Ether - 
Nitric acid 
Before Dr. Black began to deliver his che- 
mical lectuies m G lasgow in 1757, it was 
universally supposed that solids were con- 
\ cited into liquids by a small addition ot 
heat, after they had been once raised to the 
melting point, and that they returned again 
to the solid state on a very small diminution 
of the quantity of heat necessary to keep 
them at that temperature. An attentive view 
of the phenomena of liquefaction and solidifi- 
cation gradually led this sagacious philoso- 
pher to observe their inconsistence with the 
then received opinions, and to form another, 
which he verified by direct experiments, and 
drew up an account of his theory, and the 
proofs of it, which was read to a literary so- 
ciety m Glasgow on April 23d, 1762; and 
every year after he gave a detailed account 
of the whole doctrine in his lectures. 
the opinion which he formed was, that 
when a solid body is converted into a liquid 
a much greater quantity of heat enters into 
it than is perceptible immediately after by 
the thermometer. This great quantity of 
heat does not make the body apparently 
warmer, but it must be thrown into it in order 
to convert it into a liquid; and this great 
<u kill ion of heat is the principal and most ini- 
mediate cause of the fluidity induced On 
the other hand, when a liquid body assumes 
the form ot a solid, a very great quantity of 
heat leaves it without sensibly diminishing 
its temperature; and the state of solidity cam 
no! it induced without the abstraction of 
ibis great quantity of heat. Or, in othe 
words, whenever a solid is converted into 
limct, it combines with a certain dose of ca 
FLUIDITY. 
loric, without any augmentation of its tempe- 
rature ; and it is this dose of caloric which 
occasions the change of the solid into u fluid. 
W hen the fluid is converted again into a 
solid, the dose ot caloric leaves it, without 
any diminution of its temperature ; audit is 
this abstraction which occasions the change. 
I iius the combination of a certain dose of 
caloric with ice causes it to become water, 
and the abstraction of a certain dose of ca- 
loric from water causes it to become ice. 
M ater then is a compound of ice and caloric; 
and in general all fluids are combinations of 
the solid, to which they may be converted by 
the application of cold, and a certain dose of 
caloric. 
Such is the opinion concerning the cause 
of fluidity taught by Dr. Black as early as 
1762. Us truth was established by the fol- 
lowing experiments: 
First. If a lump of ice, at the temperature 
of 22°, is brought into a warm room, in a 
very short time, it is heated to 32°, the freez- 
ing point. It then begins to melt; but the 
process goes on very slowly, and several 
hours elapse before the whole ice is melted. 
During the whole of that time its tempera- 
ture continues at 32°; yet as it is constantly 
surrounded by warm air, we have reason to 
believe that caloric is constantly entering into 
it. Now as none of this caloric is indicated 
by the thermometer, what becomes of it, un- 
less it has combined with that portion of the 
ice which is converted into water, and unless 
it is the cause of the melting of the ice ? 
Dr. Black took two thin globular glasses, 
four inches in diameter, and very nearly of 
the same weight. Both were filled with wa- 
ter; the contents of the one were frozen into 
a solid mass ot ice, the contents of the other 
were cooled down to 33°; the two glasses 
were then suspended in a laige room at a dis- 
tance from all other bodies, the temperature 
of the air being 47°. In half an hour the 
thermometer placed in the water-glass rose 
from 33° to 40°, or 7 degrees; the ice was at 
first 4 or 5 degrees colder than melting snow, 
but in a few minutes the thermometer ap- 
plied to it stood at 32°. The instant of time 
when it reached that temperature was noted, 
and the whole left undisturbed for ten hours 
and a half. At the end of that time the whole 
ice was melted, except a very small spongy 
mass, which floated at the top, and disaji- 
peared in a few minutes. The temperature 
of the ice water was 40°. 
Lius 10f hours were necessary to melt the 
ice, and raise the product to the temperature 
of 40°. During all this time it must have been 
receiving heat with the same celerity as the 
water-glass received it during the first half- 
hour. Idie whole quantity received then 
was 21 times 7, or 147°; but its temperature 
was only 40°: therefore 139 or 140 degrees 
had been absorbed by the melting ice, and 
remained concealed hi the water into which 
it had been converted, its presence not being 
indicated by the thermometer. 
That caloric, or heat, is actually entering 
into the ice, is easily ascertained by placing 
the hand on a thermometer under the vessel 
containing it. A current of cold air may be 
perceived descending from it during* the 
whole time of the process. 
But it will be said, perhaps, that the heat 
which enters into the ice does not remain 
5 B 2 
7^7 
there, but is^ altogether destroyed. This 
opinion is refuted by the following experi- 
ment. 
Second. If, when the thermometer is at 
22°, we expose a ve.-sel full of water at 52° to 
the open air, and beside it another vessel full 
ot bruie at the same temperature, with ther- 
mometers in each, we shall find that both of 
them gradually lose caloric, and are cooled 
down to 32°. After this the brine (which 
does not freeze till cooled down .to 0°) con- 
tinues to cool without interruption, and gra- 
dually reaches 22°, the temperature ot the 
air, but the pure water remains stationary at 
32°. It freezes, indeed, but very slowly ; and 
during the whole process its temperature is 
32°. JSow, why should the one liquid refuse 
all on a sudden to give out caloric and not 
the other? Is it not much more probable 
that the water, as it freezes, gradually gives 
out the heat which it had absorbed during its 
liquefaction ; and that this evolution main- 
tains the temperature of the water at 32% 
notwithstanding what it parts with to the air 
during the whole process? We may easily 
satisfy ourselves that the water while congeal- 
ing is constantly imparting heat to the sur- 
rounding air; lor a delicate thermometer sus- 
pended above it is constantly affected by an 
ascending stream of air less cold than the air 
around. 4 he following experiment, first 
made by Fahrenheit, and afterwards often 
repeated by Dr. Black and others, affords a 
palpable evidence, that such an evolution of 
caloric actually takes place during congela- 
tion. 
Third. If, when the air is at 22°, we ex- 
pose to it a quantity of water in a tail beer- 
glass, with a thermometer in it and covered, 
the water gradually cools down to 22° With- 
out freezing. It is* therefore 10° below the 
freezing j oint. Things being in this situa- 
tion, if the water is shaken, part of it in- 
stantly freezes into a spongy mass, and the 
temperature of the whole instantly rises to 
the freezing point, so that the water ha . ac- 
quired ten degrees of caloric in an instant. 
Now whence came these ten degrees? Is ifc 
not evident that it must have come from that 
part of the water which was frozen, and con- 
sequently that water in the act of freezing 
gives out caloric ? ® 
from many experiments made cn water in 
these circumstances, it is found that the quan- 
tity of ice which forms suddenly on the agita- 
tion of water, cooled down below the freezing 
point, bears always a constant ratio to the 
coldness of the liquid before agitation. Thus 
" hen water is cooled down to 22° very nearly 
.J-p ot the whole freezes; when the previous 
temperature is 27°, about of the whole 
freezes. In all cases when water is cooled 
down below 32°, it loses a portion of the ca- 
loric which is necessary to constitute its liqui- 
dity. The instant that such water is agitat- 
ed, one portion of the liquid seizes upon the 
quantity of caloric in which it is deficient, at 
the expence of another portion, which of 
course becomes ice. Thus when water is 
cooled down to 22°, every jiarticle of it wants 
lCBofthe caloric necessary to keep it in a 
state of liquidity. Thirteen parts of it seize 
f0 degrees each from the lourteenth part. 
These thirteen of course acquire the tempera- 
ture ot 32° ; and the other part, being depriv- 
ed of 10 X 13 = 130, which with the tea de- 
