EUDIOMETER Y. 
sieu. Essential character : corolla inferior, 
six-parted, permanent, spreading ; filaments 
united at the base into a nectary growing 
to the corolla. There are four species, all 
natives of the Cape. 
EUDIOMETRY. The measurement of 
the quantity of oxygen contained in atmo- 
plieric air, or indeed in any gas in which 
it is not intimately combined, is named eu- 
diometry, and the instrument by which it is 
performed, the eudiometer. To attain such 
a measurement, it is merely necessary to 
present to atmospheric air, some substance 
which combines with its oxygen, and which 
either does not afford any gaseous product, 
or affords one that is easily abstracted and 
measured. Different substances have been 
applied to this purpose. 
The fluid originally employed by Scheele, 
in the analysis of the air, the solution of sul- 
phuret of potash, or what is rather more 
convenient, the sulphuret of lime, is perhaps 
superior in accuracy to any, at least if the 
air be not too long exposed to it, and be 
not in too small quantity proportioned to 
the quantity of fluid. Phosphorus is applied 
by a very simple apparatus, but by its so- 
lubility in nitrogen gas, it adds to the bulk 
of the residual air, for which a correction 
must be made. Nitrous gas was employed 
by Priestley, it exhibits the result imme- 
diately, but is liable to several sources of 
fallacy. Hydrogen gas was employed by 
Volta: a given measure of it being put 
along with a quantity of the air, designed 
to be submitted to trial, into a graduated 
tube, add inflamed by the electric spark, 
the diminution of volume indicating the 
quantity of oxygen ; 100 measures of oxy- 
gen require rather less than 200 measures 
of hydrogen for saturation ; about 40 mea- 
sures of hydrogen are therefore sufficient to 
saturate the oxygen contained in 100 mea- 
sures of atmospheric air, but it is proper to 
use an excess of hydrogen, as otherwise 
part of the oxygen is liable to escape com- 
bination. From 60 of hydrogen, with 100. 
of atmospheric air, Mr. Dalton states, that 
the residuum after explosion is 100, 21 of 
oxygen combining with 39 of hydrogen. 
The method is simple and expeditious, and 
as Humboldt and Gay Lussac have remark- 
ed, has the great advantage, from the bulk 
of the mixture, and the great diminution of 
volume, from the consumption of a given 
quantity of oxygen, of being more delicate 
than any other. It also requires no correc- 
tions for variations of temperature or atmo- 
spheric pressure ; and any impurity in the 
hydrogen gas, which it has been supposed 
might be a source of error, may be avoided 
by care. It affords also the best method 
of determining the purity of oxygen gas, or 
the proportion of oxygen in any mixed gas 
containing it. Humboldt and Gay Lussac, 
in an elaborate memoir, have pointed out 
all the circumstances to be attended to in 
employing it as an eudiometer. (Journal 
de Physique, t. lx. p. 129.) 
From the practice of eudiometry, it was 
at one time expected, as the name implies, 
that we should be able to ascertain the pu- 
rity of the air, with regard to its salutary or 
noxious power on life. It was soon found, 
however, particularly by Priestley, (and the 
fact has also since been established by De 
Marti), that the air of places the most of- 
fensive and unhealthy, afforded as much 
oxygen as that of others of an opposite de- 
scription ; the air, for example, of crowded 
cities, of low, damp situations, or of crowd- 
ed manufactories, has not been found less 
pure than that of the country ; the noxious 
quality of the air depending not so much on 
any deficiency of oxygen, as on the pre- 
sence of effluvia not discoverable by this 
test. 
It was at one time imagined, that the 
composition of atmospheric air is not uni- 
form, but that it varies both at different 
parts of the earth’s surface, and still more 
at different heights. Ingenhouz made a 
number of experiments to prove the former 
fact, from which he concluded, that the air 
is purer, or contains more oxygen at sea 
than on land, and that in the neighbour- 
hood of marshy situations it contains less 
oxygen than the standard. (Philosophical 
Transactions, vol. lxx. p. 354). 
Saussnre made some experiments on the 
air at some of the elevated parts of the 
Alps, the summit of the great St. Bernard, 
the Buet, &c. ; in this air the proportion of 
oxygen was less than in the air on the 
plains. (Voyages, t. ii. p. 357 ; t. iv. p. 451.) 
Von Humboldt relates also, that air 
brought from a great height in the atmo- 
sphere, by a person who had ascended in a 
balloon, contained in 100 parts 25.9 of oxy- 
gen, while air at the surface contained 27.6 ; 
and that at the summit of the Peak of Te- 
neriffe, the proportion of oxygen amounted 
only to 19, while at the foot of the moun- 
tain it was 27. The proportions which he 
states prove sufficiently the error of the eu- 
diometrical method he employed, and the 
eudiometer he did use, that with nitrous 
gas, corrected by trying its purity with sul- 
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