386 C H E M I 
cold air, preferved in that Rate by means of the frigorific- 
mixture in the exterior vefiel, and which furrounds the 
jar. Fig. 6, in the fame plate, reprefents the apparatus 
employed in the large experiment, which is fimilar in its 
.arrangement to the former; only that the cold atmofphere 
round the japanned pail had no exterior cold mixture to 
defend it; which, however, was the iefs neceffary, as the 
earthen-pan was of considerable thicknefs, and had ac- 
quiied the temperature of the mixture that had been em¬ 
ployed in cooling the five pounds of muriat of lime. 
In experiments.of this kind, all the exterior veffels 
Ihould be of earthen-ware or wood, which, being bad 
conductors of heat, prevent the ingredients from re¬ 
ceiving heat from the atmofphere and furrounding .objects 
"with the fame facility that they would through metals ; 
and, for a fimilar reafon, the interior veffels are belt of 
metal, that they may allow the heat to pafs more readily 
from the fubllance to be cooled into the frigorific mixture 
employed for that purpofe. 
Muriat of lime is certainly the moll powerful, and at 
the lame time the molt economical fubllance, that can 
be employed for producing artificial cold; for its fir It coft 
is a mere trifle, being a refiduum from many chemical 
jiroceffes, as the diftillation of pure ammonia, See. and 
often thrown away: befides it may be repeatedly ufed for 
limilar experiments, nothing being neceffary for this 
purpofe but filtration and evaporation to bring it to its 
firlt Hate. The evaporation Ihould be carried on till the 
folution becomes as thick as a ltrong fyrup, and,' upon 
cooling, the whole wiil become cryltallized: it mull then 
be powdered, put up in dry bottles, weil corked, and co¬ 
vered with bladder or cement, to prevent liquefaction ; 
which otherwife would foon take place, owing to the 
great affinity the muriat has for moilture. 
The powerful effefts produced by the frigorific mixture 
of muriat of lime and l'now, prefentsa wide field for ex¬ 
periments, to determine the pofiibility of fixing fame of 
the gafes by intenfe cold. 
NEW STEEL-YARD for WEIGHING GASES, See. 
This ingenious apparatus is the invention of C. Paul, 
public infpeCtor of weights and meafures in the city of 
Geneva. Erefledon a large fcale,. it may fervefor weigh¬ 
ing in the ufual manner, and according to any fyltem of 
weights, all ponderable bodies, to the precifion of half a 
grain in the weight of a hundred ounces; or, in other 
words, of a ten thoufandth part. It is employed, befides, 
for ascertaining the fpecific gravity of folids, of liquids, 
and even of the air itfelf, by proceffes extremely fimple, 
and which do not require many fub-divilions in the . 
weights. This complete apparatus is reprefented in the 
Chemiftfy Plate X. fig. i. 
The beam A B, is conftruCted on the fame principles 
as the commercial fteel-yard, but of much fmaller dimen- 
fion- The fhears are fufpended by a ferew to a crofs bar 
cf wood fupjJpYted by two pillars, which reft on the two 
extremities of a fmall wooden box furnilhed with three 
drawers, and which ferves 3s the ftand of the apparatus. 
This beam is divided into ioo parts, beginning at its 
centre of motion. The divifion is differently marked on 
the two faces: on the anterior face the numbers follow 
each other from ten to 200, proceeding towards the ex¬ 
tremity ; and on the other face, reprefented apart at F, 
the numbers are marked in the oppolite d.reCtion. 
The fmall frame G, is deftiped to prevent the ofcilla- 
tion. of the beam, and it is placed at the proper height, 
by means of the nut and ferew by which it is fufpended. 
Above the beam is a fmall crofs bar of brafs, fulpended 
by its two extremities from the crofs bar of wood. Dif¬ 
ferent weights are hooked to it, each having its particu¬ 
lar value marked on it. And, in the la(t place, a fmall 
mercurial thermometer, having the two molt ufual divi- 
fions, and deftined to point out the temperature of the 
air and the water during the experiments. The axis of 
fulpenfion of the Iteel-yard refts upon two beds of very 
2 
_S T R Y. 
bard well-poliftrad Heel. The cafe is the fame, but in a 
reverfed fituation, with the axis which fupports the hook 
C, that ferves for l'ufpending different parts of the appa¬ 
ratus according to the purpofe to which it is to be applied. 
When you wilh to employ it as a common fteel-yard, 
>ou fufpend from it the brafs (liell E, which is an exadt 
counterbalance for the weight of the beam when unload¬ 
ed. The latter then affumes of itfelf a horizontal fitua¬ 
tion. You then learch for the equilibrium of the fub- 
ftance put into this (hell, by fixing at the proper place, 
on the beam, the weight and its fradtions correfponding 
with the fyltem of weights adopted ; and when you have 
found the equilibrium, you obferve the w’eight indicated 
by the divifions on which each of the weights employed 
is found, exadtly in the fane manner as is done in regard 
to the common lleei-yard. 
There is a glafs fiiell fufpended in a jar, filled to a cer¬ 
tain height with water. This fiiell is deftined for expe¬ 
riments in regard to the fpecific gravity of folids. It is 
in equilibrium,if, when immerfed in water at 12 0 of Reau- 
mer, as far as the junction of'the three filver wires by 
which it is fupported, it exadtly balances the weight of 
the beam unloaded. When you wilh to try the fpecific 
gravity of a folid, you firlt weigh it in air; but by putting 
it into the brafs fiiell, and then fubllituting the glafs one, 
you weigh it in water. It is well-known that the differ¬ 
ence of thefe weights, employed as a divifor of the total 
weight in air, gives for quotient the fpecific gravity. 
Care muff be taken, as in all experiments of the kind, 
that no bubble of air adheres to that part of the appara¬ 
tus immerfed in the water, or to the fubllance, the weight 
of which is required, and which is immerjed alfo. 
The folid glafs ball H, is deftined for the purpofe of 
afeertaining the fpecific gravity of liquids, in the follow¬ 
ing manner: This piece is furnilhed with a hook of fine 
gold, that it may be immerfed without inconvenience in 
acids. When it is fufpended to the hook of the Iteel-yard, 
and in the air, it is in equilibrium with the beam loaded 
at its extremity (either at the divilion marked O, on the 
fide of the beam feen at F) with weights entitled fpecific , 
and -j-'oo of fpecific hooked on at the other. 
Tliis ball, immerfed in diftilled water at 12 0 of Reau- 
mer, as far as the end of the ftraight metal wire which 
fufpends it, is ftill in equilibrium with thefe two weights 
placed in the following manner, viz. the large one at the 
divifion in the middle of the beam marked water on the 
fide F of the beam, and the fmall one at the divifion O, 
that is to fay, the extremity. When the apparatus is 
thus prepared, you fill a jar with the liquid, the fpecific 
gravity of which you wifh to afeertain ; fufpend the ball 
H to the hook of the fteel-yard, and immerfe.it into the 
liquid till it rife exaftly above the ring from which the 
ball hangs, obferving the temperature, and diiengaging 
carefully all the air bubbles that may adhere to the bali; 
then remove the fmall weight to the divifion O, at the 
end of the beam, and convey the large one as far as that' 
divifion, preceding that where the weight of the ball 
would raife the beam ; and afterwards move the final! 
weight as far as the divifion where the equilibrium will 
be reftored, the beam being horizontal. Mark the divi¬ 
fion at which the large weight is found, and add two cy¬ 
phers; to this number add the indication immediately re- 
iulting from the pofition of the final! weight, and the lum 
of thefe two numbers gives the fpecific gravity of the li¬ 
quid, or its ratio, with the weight of diltilled water to a ten 
thoufandth part. 
The balloon N, is deftined for trying the weight of 
any given kind of gas, compared with that of atmolphe- 
ric air, in the following manner : The weight entitled 
air tare , is arranged in f'uch a manner that when placed 
in the notch, feen at the extremity of the beam beyond 
the divifions towards B, it forms an equilibrium with 
the balloon exhaufted by the air-pump and fufpended 
from the hook of the fteel-yard. If the fteel-yard is net 
then ill equilibrium, it is a fign that the; inftrument is 
• * deranged,' 
i. 
1 
