212 
C H E M 
acid in freffi vegetables, efpecially fuch as are fufceptible 
of fermentation, as the decoftionof barley which has been 
flittered to germinate, or the infufion of raitins, &c. all 
which he thinks are equally ferviceable in f'eptic or fcor- 
butic diforders, Water impregnated with carbonic acid, 
has likewiie, in feveral cafes, been fuccefsfutly prefcribcd 
in putrid, bilious, fevers, in pulmonary complaints, and 
various diforders of the lungs. It has been ftrongly re¬ 
commended as a lithontriptic, or folvent of the hone in 
the bladder ; but we are nor in pofteffion of any authen¬ 
ticated fafts in proof of its efficacy in that complaint. 
The public prints contain accounts of feveral inftances 
of the cure of the cancer made by the application of-the 
■carbonic acid. We can nevertheleis aifert, that this 
means has been ufed feveral times without luccefs. Af¬ 
ter the firft application, the cancerous ulcer exhibits a 
more favourable appearance; the fanies, which com¬ 
monly flows, becomes white, confiftent, and laudable ; 
the flefli affumes a lively colour : but thefe flattering ap¬ 
pearances do not continue ; the ulcer foon returns to its 
former ffate, and paffes through the ufual changes with 
unabated violence. It is to the firft difcovery of this acid 
■ by Dr. Black that we mult fix one of the molt brilliant epo- 
ciias of chemiltry. To determine the influence of this 
.difcovery on the fcience, we fhall here offer the following 
remarks: i. It has added one to the number of acids. 
2. It has fliown the caufe of the effervefcence which 
.mild alkalis, chalk, calcareous ipar, and magnefia, pro¬ 
duce with ftronger acids than itlelf. sdly, It has caufed 
a diitindlion to be made of all alkaline matters into two 
lfates, the ftate of purity or caufticity, and the mild 
ftate, having the property of effervefcence. qthly, It 
has greatly enlightened the hiftory of the elective attrac¬ 
tions of acids for ammoniac and lime, fthly. It exhibits 
the firlt inftance of an acid which prefers lime to fixed 
alkalis. 6thly, The hiftory of mephitic caverns, in which 
animals cannot live, is become very clear and fimple, in 
confequence of this difcovery. 7thly, The analyfis of 
.waters has been rendered more perfeft from the accurate 
knowledge of fuch as are called gafeous, fpirituous, aci¬ 
dulous, and in confequence of that knowledge we 
have fucceeded in perfeftly imitating them. Stilly, It 
has thrown great light on the folution of iron in many 
waters, and on the means of procuring martial waters 
entirely fimilar to thofe in nature. 9thly, It has exhi¬ 
bited a clafs of neutral earthy, alkaline, and metallic 
halts, in which the carbonic acid is a principle part; and 
which are diftinguiflied in this Treatife by the generic 
name of carbonats. Laftly, It has opened a new field to 
the refearches of chemifts, and has excited that ardour 
to which we are indebted for all the brilliant dilcoveries 
made fince that period. 
The carbonic acid gas is the choks-datnp of miners, fo 
called from the fatal effefits it produces on thofe who 
breathe it. The miners are Informed of its prefence, by 
the faintnefs with which their lights burn, or by their 
total extinction. It is fynonymous with the fixed air of 
the Engliffi chemilts 5 the mephitic acid of M. Bewly ; 
the mephitic gas of Macquer 5 the aerial acid of Bergman; 
and the cretaceous acid of Bucquet. It exifts in^great 
abundance in chalk, limeltone, marble, calcareous fpars, 
&c. forming nearly one third of their fubitance. Jt is 
alio extricated in confiderable quantity from putrefying 
animal matter. According to Lavoifier, its fpecific gra¬ 
vity is to that of common atmofpherical air, in the pro¬ 
portion of 1-8454 to i’23o8. 
Of PHOSPHORIC ACID. 
It was long fuppofed that this acid exifted ready form¬ 
ed in phofphorus; but Lavoifier has demonftrated that 
it is a combination of phofphorus with oxygen, He af¬ 
firms that too parts of phofphoric acid is composed of 
■28J- parts of phofphorus united to 71-t parts of oxygen. 
Methods of obtaining phofiphoric acid. —1. By the rapid 
cojabuftion of phofphorus in oxygen gas, it is obtained 
a 
.A 
I S T R Y. 
in white flakes. 2. By paffing a flream of vita! air thro' 
phofphorus melted under water. Thefe experiments are 
already detailed in page 201. 3. By decompofition of 
bones. 4. By nitric acid. In treating of thefe two daft 
fubftances, we fhall defcribe their aftion and manner of 
operating, 
Its properties. —Obtained, without the addition of wa¬ 
ter, in vital air, it is in white flakes, fnovvy, light, deii- 
quefcent, and with a tafte very ftrongly acid. Expofed 
to the air, it attracts its humidity very ftrongly. In con¬ 
tact will water, it eafily melts, furnidling-a white fluid, 
without fmell, of an oily confidence, very heavy. Ex¬ 
pofed to the aCtion of fire in a clofe retort, a clear water 
is produced ; the acid concentrates, and becomes heavier 
that fulphuric acid ; it gains confidence and opacity by 
degrees; by leaving it to thicken, ftill more, it becomes 
like a jelly. In a violent heat, it vitrifies, melting into 
a tranfparent, hard, and very eleCtric, glafs. If this vi¬ 
treous phofphoiic acid be expofed to the air, it foftens it, 
and by degrees makes it become entirely liquid. 
Phofiphoric acid and hydrogen gas. —Put vitreous pliof- 
phorie acid into a porcelain tube, and to the upper ex¬ 
tremity fix the apparatus already deferibed for obtain¬ 
ing h)’drogen gas; the other extremity is to be furniflied 
with a tube, which goes into a two-necked bottle, whence 
is lent out another tube which is palled under an invert¬ 
ed jar in the pneumatic apparatus. The tube muft be 
made red-hot to melt the phofphoric acid, and the hy¬ 
drogen gas is to be palled through it. The hydrogen de¬ 
prives the acid of its oxygen ; water is formed 3 and at 
the end of the operation phofphorus is found in the tube. 
Phofiphoric acid and charcoal. —Take phofphoric acid of 
the confiftence of jelly; add powder of charcoal, very 
dry, about one-fourth of the weight of phofphorus, or 
as much as will.make the Inals of a friable confiftence; 
dry the mixture in a melting-pot, until the greater part of 
themoifturebediffipated. Then put the mixture into a luted 
earthen retort, and an inverted retort, containing water,_ 
is-uled for a receiver; but Pelletier recommends a re¬ 
ceiver of copper, lhaped like an inverted retort. Put 
water into the receiver in fuch a manner, that the phof¬ 
phorus, as it paffes off, may be flopped, and not come 
in contaft with the air. By this method, a great quan¬ 
tity of phofphorus efcapes combullion, fince it mull pafs 
through a column of water of fix inches before it comes 
in contafit with the air. The apparatus thus prepared, 
bring the retort by degrees to a very ltrong flaming heat 
in a reverberatory furnace. In the early Itage of the ope¬ 
ration, hydrogen gas and carbonie acid are difen gaged, 
arifing from the decompofition of the water by the char¬ 
coal. When the pholphoric acid begins to be decom- 
poled, the hydrogen gas diflfolves a little phofphorus, 
which gives it the property of flaming in the dark by the 
contact of air; finally, when the heat is ftrong enough, 
the phofphorus is converted into an oil, which falls into 
the water of the recipient, and there coagulates. This 
experiment fhews, that at a high temperature the carbon 
has more affinity with the oxygen than the phofphorus 
lias.; that this laft has more than the hydrogen, Alice 
water is decompofed before phofphoric acid ; laftly, that 
hydrogen is capable of diffolving a certain quantity of 
phofphorus. It appears that the water of the receiver 
keeps the hydrogen pliofphorated ; for, as foon as it is 
expofed to the air in the dark, even after filtration, it 
throws out very bright pholphoric fparks, efpecially 
when the furfaces are renewed by agitation. 
By heating phofphoric acid over oxyd of phofphorus, 
the oxyd changes the pholphoric acid into phofphorous 
acid. Sulphur will not decompofe phofphoric acid; but 
it unites with metallic oxyds, and forms falts, as yet but 
little known. 
PHOSPHOROUS ACID. 
To produce this acid, which is phofphorus lefs oxyge¬ 
nated than in the ftate of phofphoric acid, the phophorus 
muft 
