C6Q 
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examined and hydrogen gas in a graduated 
glass tube; to fire the mixture by an electric 
spark; and to judge of the purity of the air 
by the bulk of the residuum. But this me- 
thod is not susceptible of even so great a de- 
gree of accuracy as the preceding, when the 
object is to ascertain the precise quantity of 
oxygen gas in a given bulk of air. For if too 
little hydrogen gas is mixed with the air, not 
only the whole of the oxygen will not be abs- 
tracted, but a portion of the azote will dis- 
appear in consequence of the formation of 
nitric acid. On the other hand, if too much 
hydrogen is added, part of it will remain after 
the tiring of the mixture, and increase the 
bulk of the residuum. Volta’s eudiometer, 
then, though it may have its uses, is scarcely 
susceptible of giving us the analy sis of air. 
3. For the third kind of eudiometer, we 
are indebted to Scheele. It is merely a gra- 
duated glass vessel, containing a given quan- 
tity of air exposed to newly prepared liquid 
alkaline or earthy sulphurets, or to a mixture 
of iron-filings and sulphur, formed into a paste 
with water. These substances absorb the 
whole of the oxygen of the air, which con- 
verts a portion of the sulphur into an acid. 
The oxygen contained in the air thus exam- 
ined, is judged of by the diminution of bulk 
which the air has undergone. This method 
is not only exceedingly simple, but it requires 
very little address, and yet is susceptible of 
as great accuracy as any other whatever. 
The only objection to which it is liable is its 
■slowness; for when the quantity of air ope- 
rated on is considerable, several days elapse 
before the diminution has reached its maxi- 
mum. 
But this objection has been completely ob- 
viated by M. De Marti, who has brought 
Scheele’s eudiometer to a state of perfection. 
He found that a mixture of iron-filings and 
sulphur does not answer well, because it 
emits a small quantity of hydrogen gas, 
evolved by the action of the sulphuric acid 
formed by the absorption of the oxygen of 
the air upon the iron ; but the hydrogureted 
sulphurets, formed by boiling together sul- 
phur and liquid potass or lime-water, an- 
swered the purpose perfectly. These sub- 
stances, indeed, when newly prepared, have 
the property of absorbing a small portion of 
azotic gas ; but they lose this property when 
saturated with that gas, which is easily effect- 
ed bv agitating them for a few minutes with 
a small portion of atmospheric air. His ap- 
paratus is merely a glass tube, ten inches 
long, and rather less than half an inch in dia- 
meter, open at one end, and hermetically 
sealed at the other. The close end is divided 
into 100 equal parts, having an interval of 
one line between each division. The use of 
this tube is to measure the portion of air to 
be employed in tire experiment. The tube 
js filled with water; anti by allowing the wa- 
ter to run out gradually while the tube is in- 
verted, and the open end kept shut with the 
finger, the graduated part is exactly filled 
with air. These hundredth parts of air are in- 
troduced into a glass bottle filled with liquid 
suiphuret of lime previously saturated with 
azotic gas, and capable of holding from two 
to four times the bulk of the air introduced. 
The bottle is then to be corked with a ground 
glass stopper, and agitated for five minutes. 
Alter this the cork is to be withdrawn while 
tfie mouth of the phial is under water; and 
for the greater security, it may be corked 
and agitated again. After this, the air is to 
be again transferred to the graduated glass 
tube, in order to ascertain the diminution of 
its bulk. 
Air, examined by this process, suffer, pre- 
cisely the same diminution in whatever cir- 
cumstances the experiments are made: no 
variation is observed whether the wind is 
high or low, or from what quarter soever it 
blows; whether the air tried is moist or dry, 
hot or cold; whether the barometer is high 
or low. Neither the season of the year, nor 
the situation of the place, its vicinity to the 
sea, to marshes, or to mountains, makes any 
difference. M. De Marti found the dimi- 
nution always between 0.21 and 0.23. Hence 
we may conclude that air is composed of 
0 78 azotic gas 
0.22 oxygen gas. 
1.00 
Scheele indeed found, that the absorption 
amounted to 0.27 ; but that was because he 
neglected to saturate his suiphuret with azo- 
tic gas ; for when the portion of azotic gas 
which must have been absorbed, and which 
has been indicated by De Marti, is subtract- 
ed, the portion of oxygen in air, as indicated 
by his experiments, is reduced very nearly 
to 0.22. The trifling variations perceptible 
in his experiments were no doubt owing to 
the quantities of the mixture of sulphur and 
iron, by which he abstracted the oxygen, not 
being exactly the same at different times ; 
the consequence of which would be, an un- 
equal absorption of azotic gas. 
4. In the fourth kind of eudiometer, the 
abstraction of the oxygen of air is accom- 
plished by means of phosphorus. This eu- 
diometer was first proposed by Achard. It 
was considerably improved by Reboul, and 
by Seguin and Lavoisier; but Berthollet has 
lately brought it to a state of perfection, as it 
is equally simple with the eudiometer of De 
Marti, and scarcely inferior to it in preci- 
sion. 
Instead of the rapid combustion of phos- 
phorus, this last philosopher has substituted 
its spontaneous combustion, which absorbs 
the oxygen of air completely ; and when the 
quantity of air operated on is small, the pro- 
cess is over in a short time. The whole ap- 
paratus consists in a narrow graduated tube 
of glass containing the air to be examined, 
into which is introduced a cylinder of phos- 
phorus fixed upon a glass rod, while the tube 
stands inverted over water. The phospho- 
rus should be so long as to traverse nearly 
the whole of the air. Immediately white va- 
pours rise from the phosphorus and fill the 
tube. These continue till the whole of the 
oxygen combines with phosphorus. They 
consist of phosphorous acid, which falls by its 
weight to the bottom of the vessel, and is 
absorbed by the water. The residuum is 
merely the azotic gas of the air, holding a 
portion of phosphorus in solution. Berthollet 
has ascertained, that by this foreign body its 
bulk is increased one-fortieth part. Conse- 
quently, the bulk of the residuum, diminish- 
ed by - 1 -, gives us the bulk of the azotic gas 
of the air examined; which bulk, subtracted 
from the original mass of air, gives us the 
proportion of oxygen gas contained in it. 
All the different experiments which have 
E T I 
been made by means of this eudiometer, I 
agree precisely in their result, and indicate 1 
that the proportions of the ingredients of air I 
are always the same, namely, about 0.22 I 
parts of oxygen gas, and 0.78 of azotic gas. I 
Berthollet found these proportions in Egypt I 
and in France, and Dr. Thomson found ] 
them constantly in Edinburgh in all the dif- I 
ferent seasons of the year. Thus we see that I 
the analysis of air by means of phosphorus, j 
agrees precisely with its analysis by means of | 
hydrogureted sulphurets. 
5. The fifth eudiometer has been lately 1 
proposed bv Mr. Davy. In it the substance j 
used to absorb the oxygen from air is a so- i 
lotion of sulphat or muriat of iron in water, J 
and impregnated with nitrous gas. A small 
graduated glass tube, filled with the air to be ] 
examined, is plunged into the nitrous solu- j 
tion, and moved a little backwards and for- j 
wards. The whole of the oxygen is absorb- 
ed in a few minutes. The state of greatest 
absorption ought to be marked, as the mix- 1 
ture afterwards emits a little gas which would | 
alter the result. By means of this and thel 
two preceding eudiometers, Mr. Davy ex-1 
amined the air at Bristol, andfound it always] 
to contain about 0.21 of oxygen. Air sent to 
Dr. Beddoes from the coast of Guinea gave] 
exactly the same result. This eudiometer, | 
then, corresponds exactly with the two last. | 
In all these different methods of analysing | 
air, it is necessary to operate on air of a de«] 
terminate density, and to take care that thel 
residuum is neither more condensed nor di-J 
lated than the air was when first operated on.l 
If these things are not attended to, no de-j 
pendance whatever can be placed upon the rtf- 
suit of the experiments, how carefully soever! 
they may have been performed. Now there! 
are three tilings which alter the volume of] 
air and other elastic fluids: 1. A change in] 
the height of the barometer. 2. An increase! 
or diminution of their quantity ; the vessel! 
in which they are contained remaining the 
same, and standing in the same quantity of 
water or mercury. 3. A change in the tenul 
perature of the air. 
EVERGREEN, in gardening, a species] 
of perennials which continue their verdureja 
leaves, &c. all the year: such are hollies J 
phillyrias, laurustinuses, bays, pines, firsd 
and cedars of Lebanon. See Gardening'.] 
EVES-DROPPERS, are such as standj 
under walls or windows, by night or day, to 
hear news, and to carry them to others, to 
cause strife and contention among neigh- 
bours. These are evil members in the com- 
monwealth, and therefore by stat. Westmin- 
ster 1. c. 33, are to be punished; and this 
misdemeanor is presentable and punishable in 
the court leet. 
EUGENIA, the yamboo, a genus of the] 
monogynia order, in the icosandria class of] 
plants, and in the natural method rankina 
under the 19th order, hesperidea?. The ca-] 
lyx is quadripartite, superior ; the petals four J 
the fruit a monospermous quadrangular plumJ 
There are 1 1 species, natives of the hot parts 
of Asia and America. They rise from 20 to] 
30 feet high; and bear plum -shaped fruit, iu-j 
closing one nut. They are too tender to] 
live in this country, unless they are constant-] 
ly kept in a stove. 
EV ICTION, in law, signifies a recovery 
of lands or tenements by law. 
When lands, &c. are evicted before real 
