COLD. 
766 
The effefts produced on mod bodies by the agency of 
cold, are extremely curious and interelting. In general, 
cold contracts molt' bodies, and heat expands them : 
though there are fome inttances to the contrary, efpe- 
daily in the extreme Hates of thefe qualities of bodies. 
Thus, though iron, in common with other bodies, ex¬ 
pands with heat, yet, when melted, it is always found 
to expand in cooling again. So alfo, though water al¬ 
ways is found to expand gradually as it is heated, and to 
contract as it cools, yet in the aft of freezing it fuddenly 
expands again, and that with a mod enormous force, ca¬ 
pable of rending rocks, or burlting the very thick (hells 
or metal, &c. A computation of the’force of freezing wa¬ 
ter has been made by the Florentine Academicians, from 
the burlting of a very ltrong brafs globe or (hell, by freez¬ 
ing water in it; when, from the known thicknefs and te¬ 
nacity of the metal, it was found that the expanfive 
power of a fpherule of water only one inch in diameter, 
was fufticient to overcome a refinance of more than 2.7,000 
pounds, or thirteen tons and a half. Experiments have 
aKo been made on binding thick iron bomb-(hells by 
freezing water in them, by Mr. Edward Williams of the 
royal artillery, and publilhedinthe Edin.Phil. Tran, vol.i. 
Such a prodigious power of expanfion, almofl double 
that of the mod powerful deam engines, and exerted in 
fo fmall a mafs, feemingly by the force of cold, was 
thought a very powerful argument in favour of thofe who 
fuppofed that cold, like heat, is a politive lubdance. The 
late Dr. Black’s difcovery of latent heat, however, has 
now afforded a very eafy and natural explication of this 
phenomenon. He has (hewn^that, in the aft of congela¬ 
tion, water is not cooled more than it was before, but 
rather grows warmer : that as much heat is difcharged, 
and pades from a latent to a fenfible date, as, had it been 
applied to water in its fluid date, would have heated it 
to 135 0 . In this procefs, the expanfion is occafioned by 
a great number of minute bubbles fuddenly produced. 
Formerly thefe were fuppofed to be cold in the abdraft: 
and to be fo fubtle, that, infinuating themfelves into the 
fubdances of the fluid, they augmented its bulk, at the 
fame time that, by impeding the motion of its particles 
upon each other, they changed it from a fluid to a (olid. 
But Dr. Black (hews that thefe are only air extricated 
during the congelation ; and to the extrication of this 
air he afcribes the prodigious expanfive force exerted by 
freezing water. The only quedion therefore now re¬ 
maining, is. By what means this air comes to be extri¬ 
cated, and to take up more room than it naturally does 
in the fluid. To this it may be anfwered, that perhaps 
part of the heat which is difcharged from the freezing 
water, combines with the air in its unelaflic date, and, 
by reftoring its eladicity, gives if that extraordinary 
force, as is (een allb in the cafe of air fuddenly extricated 
in the explofion of gunpowder. See the article Che¬ 
mistry, p. 205, of this' volume. 
Cold alio ufually tends to make bodies eleftric, which 
are not fo naturally, and toincreafe the eledfric properties 
of fuch as are fo. And it is farther found that all fub- 
ftances do not tranfmit cold equally well j but that the 
belt conductors of eleftricity, viz. metals, are likewife the 
bed conductors of cold. It may farther be added, that 
•when the £old has been carried to fuch an extremity as 
to render any body an eleftric, it then ceafes to conduft: 
the cold fo well as before. This is exemplified in the 
practice of the Laplanders and Siberians; where, to ex¬ 
clude the extreme cold of the winter from their habita¬ 
tions the more effectually, and yet to admit a little light, 
they cut pieces of ice, which in the winter time mud al¬ 
ways be eleftric in thofe countries, and put them into 
their windows ; which they find to be much more effeftual 
in keeping out the cold than any other fubdance. 
Cold is the dedroyer of all vegetable life, when in- 
creafed to an excefiive degree. It is found that many 
garden plants and flowers, which feem to be very flout 
and hardy, go off at a little iucreafe of cold beyond the 
ordinary ffandard. And in fevere winters, nature has 
provided the bell natural defence for the corn fields and 
gardens, namely, a covering of fnow, which preferves 
fuch parts green and healthy as are under it, while fuch 
as are uncovered by it are either killed or greatly injured. 
Dr. Clarke is of opinion, that cold is owing to certain 
nitrous and other faline particles, endued with particular 
figures proper to produce fuch effefts. Hence, fal-ammo¬ 
niac, faltpetre, or fait of urine, and many other volatile 
and alkalizate falts, mixed with water, very much in- 
creafe. its degree of cold. In the Philof. Tranf. No. 274, 
M. Geoffroy 0 relates fome remarkable experiments with 
regard to the production of cold. Four ounces of fal- 
ammoniac diflolved in a pint of water, made his thermo¬ 
meter defcend two inches and three-quarters in lefs than 
fifteen minutes. An ounce of the lame fait put into 
four or five ounces of diddled water, made the thermo¬ 
meter defcend two inches and a quarter. Half an ounce 
of fal-ammoniac mixed with three ounces of i'pirit of ni¬ 
tre, made the thermometer defcend two inches and 
but, on ufing fpirit of vitriol indead of nitre, it funk two 
inches and a half. In this lad experiment it was remark¬ 
ed, that the vapours railed from the mixture had a con- 
fiderable degree of heat, though the liquid itfelf was lb 
extremely cold. Four ounces of faltpetre mixed with a 
pint of water, funk the thermometer an inch and a quar¬ 
ter; but a like quantity of fea-falt funk it only one-lixth 
of an inch. Acids always produced heat, even common 
fait with its own fpirit. Volatile alkaline (alts produced 
cold in proportion to their purity, but fixed alkalies heat. 
But the greated degree of cold produced by the mix¬ 
ture of falts and aqueous fluids, was that (hewn by Hom- 
berg; who gives the following receipt for making the ex¬ 
periment: Take a pound of corrofive fublimate, and as 
much fal-ammoniac; powder them feparately, and mix 
the powders well; put the mixture into a vial, pouring 
upon it a pint and a half of diddled vinegar, (baking all 
well together. This compofition grows fo cold, that it 
can fcarcely be held in the hand in dimmer ; and it hap¬ 
pened, ks M. Flomberg was making the experiment, that 
the matter froze. The fame thing once happened to 
M. Geoflroy, in making an experiment with fal-ammo- 
niac and water, but it never was in his power to make it 
fucceed a fecond time. If, indead of making thefe expe¬ 
riments with fluid water, it be taken in its congealed 
ftate of ice, or rather fnow, degrees of cold will be pro¬ 
duced greatly fuperior to any that have yet been menti¬ 
oned. A mixture of fnow and common fait finks Fah¬ 
renheit’s thermometer to o; pot allies a.nd pounded ice 
funk it 8 degrees farther; two affulions of lpirit of fait 
on pounded ice funk it 14-*- below o ; and byjrepeated af- 
fufions of fpirit of nitreM. Fahrenheit (unk it t0 40°-be- 
below o. This is the ultimate degree of cold which the 
mercurial theorometer will mealure ; for the mercury 
itfelf begins then to congeal; and therefore recourfe 
mud afterwards be had to (pirit of wine, naptha, or fome 
other fluid that will not congeal. The greated degree of 
cold hitherto produced by artificial means, has been 8o° 
below o : w'hich was done at Hudfon’s Bay by means of 
fnow and vitriolic acid, the thermometer ltanding natu¬ 
rally at 20 0 below o. Indeed greater degrees of cold 
than this have been fuppofed : Mr. Martin, in his Trea- 
tife on Heat, relates, that at Kirenga in Siberia, the mer¬ 
curial thermometer funk to 11S 0 below o; and profeffor 
Brown at Peterfburg, when he made the fil'd experiment 
of congealing quickfilver, fixed the point of congelation 
at 350° below o; but from later experiments it has been 
more accurately determined, that 40° below o is the 
freezing point of quickfilver. , 
The mod remarkable experiment however was made 
by Mr. Walker of Oxford, with fpirit of nitre poured on 
Glauber’s fait, the effeft of which was found to be fimilar 
to that of the fame fpirit poured on ice or fnow ; and the 
addition offal-ammoniac rendered the cold dill more in- 
tenfe. The proportions of thefe ingredients recommended 
