EUC 
£ U D 
E U 1) 
January 
February 
March 
April 
May 
June 
July 
August 
September 
October 
November 
December 
Bain 
Evaporation 
IS 1 ean 
Mean 
Water through the two 
pipes. 
Mean. 
Rain. 
Evap. 
Inch. 
Inch. 
Inch. 
1 796. 
1 797. 
1798. 
Inch. 
Inch. 
Inch, 
1.897 — 
.680 — 
1.774 + 
1 .450+ 
2.458 
1.008 
1.778 — 
.918 — 
1.122 
1.273 
1.801 
.528 
.431 — 
.070 — 
.335 
.279 
-902 
.623 
,220 — 
.295 — 
.180 
.232 
1.717 
1.485 
2.027 — 
2.443 + 
.010 
l .493 
4.177 
2.684 
.171 — 
.726 
• 
.299 
2.483 
2.184 
.153 — 
.025 
— 
.059 
4.154 
4.095 
— 
— 
.504 
.168 
3:554 
3.386 
. 
•976 
■ 
.325 
3.279 
2.954 
* 
.680 

.227 
2.899 
2.672 
~ 
1.044 
1.594 
.879 
2.934 
2.055 
.200 
3.077 
1.878 -f- 
1.718 + 
3.202 
1.484 
6.S77 — - 1Q.9J4 — 
7.379 
8.402 ' 
33.560 
25.158 
30.629— 38 
791 — 
31.259 
' 
23.725— 27 
85 7 — 
23.862 
From these experiments it appears that 
the quantity of vapour raised annually at 
Manchester is about 25 inches. If to this 
we add live inches for the dew with Mr. Dal- 
ton, it will make the annual evaporation 30 
inches. Now, if we consider the situation of 
/ England, and the greater quantity of vapour 
raised from water, it will not surely be con- 
Isidered as too great an allowance if we esti- 
mate the mean annual evaporation over the 
whole surface of the globe at 35 inches. 
, Now, 35 inches from every square inch on 
the superficies of the globe make 9-1,450 cu- 
bic miles, equal to the water annually eva- 
porated over the whole globe. 
Was this prodigious mass of water all to 
■ subsist in the atmosphere at once, it would 
“increase its mass by about a twelfth, and raise 
'the barometer nearly three inches. But this 
■ never happens; no day passes without rain 
in some part of the earth, so that pail of the 
evaporated water is constantly precipitated 
again. Indeed it would be impossible for 
the whole of the evaporated water to subsist 
in the atmosphere at once, at least in the 
state of vapour. 
EUCALYPTUS, a genus of the hexan- 
-dria inonogynia class and order. The calyx 
is superior, permanent, truncate before dow- 
ering, covered with an hemispherical deci- 
duous lid. Corolla, none ; capsule four- 
celled, opening at top, inclosing many seeds. 
There are two species, lofty trees of New 
Holland ; called also the red-gum tree, from 
a gummy matter, in which one of them, the 
resinifera, abounds. A single tree will, on 
being tapped, afford more than 60 gallons of 
juice, which when dried becomes a power- 
fully astringent gum resin, resembling that 
known in the shops by the name of kino, 
and found eminently efficacious in dysente- 
ries, &c. YY ater dissolves of it only one- 
sixth part, but it dissolves abundantly in spirit 
of wine, to which it gives a blood-red colour. 
EUCLEA, a genus of the dicecia dode- 
eandria class and order. In both male and 
female the calyx is four or five-toothed; the 
corolla four or five-parted ; the male stamina 
12 to 15. In the female, the germ is superior ; 
the styles two; berry two-celled. There is 
one species, a branching tree of the Cape. 
EUCOMIS, a genus of the class and order 
hexandria monogynia. The calyx is inferior, 
six-parted, permanent, spreading; filaments 
united at the base into a nectary growing to 
the corolla. ’1 here are four species, plants 
of the Cape. 
EL DlOMEl LR, an instrument for ascer- 
taining the purity of the atmospherical air, 
or the quantity ot oxygenous gas contained 
in it, chiefly by means of its diminution on a 
mixture with nitrous acid, or some similar sub- 
stance. 
Alter the composition of the atmosphere 
was known to philosophers, it was taken for 
granted that the proportion of its oxygen va- 
ried in different times and in different places ; 
and that upon this variation the purity or 
noxious qualities of air depended. Hence 
it became an object of the greatest import- 
ance to be m possession of a method of de- 
termining readily the quantity of oxygen in 
a given portion of rnr. Accordingly, va- 
rious methods were proposed, all of them 
depending upon the property which bodies 
possess ot absorbing the oxygen of the air 
without acting upon its azote. These bodies 
were mixed with a certain known quantity 
of atmospheric air, in graduated glass vessels 
inverted over water, and the proportion of 
oxygen was determined by the diminution of 
bulk. These instruments received the name 
of eudiometers, because they were consider- 
ed as measurers of the purity of air. The 
eudiometers proposed by different chemists 
may be reduced to five. 
1. The first eudiometer was made in con- 
sequence of Dr. Priestley’s discovery, that 
when nitrous gas is mixed with air over wa- 
ter, the bulk ot the mixture diminishes rapid- 
ly, in consequence of the combination of the 
gas with the oxygen of the air, and the ab- 
sorption of the nitric acid thus formed by 
(he water. YY hen nitrous gas is mixed with 
azotic gas, no diminution at all takes place. 
YY hen it is mixed with oxygen gas in proper 
proportions, the absorption is complete. 
Hence it is evident, that in all cases of a 
mixture ot these two gases, the diminution 
will be proportional to the quantity of the 
oxygen. Or course it will indicate 'the pro- 
portion of oxygen in air; and by mixing it 
with different portions of air, it will indicate 
the different quantities of oxygen which they 
contain, provided the component parts of 
air are susceptible of variation. Dr. Priest- 
ley’s method was, to mix together equal bulks 
of air and nitrous gas in a low jar, and then 
to transfer the mixture into a' narrow gradu- 
ated glass tube about three feet lone, in or- 
4 0 2 
a# 
der to measure the diminution of bulk. He 
expressed this diminution by the number of 
hundredth parts remaining. Thus, suppose he 
had mixed together equal parts ot nitrous 
gas and air, the sum total of this mixture was 
200 (or 2.00): suppose the residuum when 
measured in the graduated tube to "amount 
to 104 (or 1.04), and of course that 96 parts 
of the whole had disappeared, he denoted the 
purity of the air thus tried by 104. A more 
convenient instrument was invented by Dr. 
f alconer of Bath ;. and Fontana greatly im- 
proved this method of measuring the purity 
of air. A description of his eudiometer was 
published by Ingenhouz, in the first volume 
of bis Experiments: it was still farther im- 
proved by Mr. Cavendish in 1783 ; and 
Humboldt has lately made a very laborious 
set of experiments in order to bring it to a 
state of complete accuracy. But after all 
the exertions of these philosophers, the me- 
thod of analysing air by means of nitrous gas 
is liable to so many anomalies, that it cannot 
be depended on. 
Priestley and Fontana 'have proved, that 
the way of mixing the two airs occasions a 
great difference in the result : the figure of 
the vessels is equally important, and so is the 
water over u hich the mixture is made. And 
even when all these things are the same, the 
impurity of the nitrous gas may occasion the 
most enormous differences in the results. 
Humboldt has shewn that the nitrous gas 
ought to be prepared by means of nitric acid 
of the density 1.170; when a much stronger 
or weaker acid is employed, the gas produced 
is always contaminated with a great propor- 
tion of azotic gas. He has pointed out the 
solution of sulphat of iron as proper to ascer- 
tain the purity of the nitrous gas employed, 
by absorbing the nitrous gas, and leaving the 
azotic gas or other foreign gases, lie has 
shewn that when nitrous gas of the same de- 
gree of purity is made to mix very slowly 
with air, the vessel being carefully agitated 
during the mixture, the results, provided the 
experiment is performed with address, cor- 
respond with each other. And he lias made 
it probable, that when equal quantities of air 
and nitrous gas, so pure as to contain only 
about 0.1 of azotic gas mixed with it, are 
agitated together slowly over water, the di- 
minution divided by 3.55, gives the quantity 
of oxygen contained in the air examined. 
But notwithstanding the ingenuity of his ex- 
periments, the anomalies attending this me- 
thod are still so great as not to render it sus- 
ceptible of accuracy. For that reason it is 
unnecessary to give a particular description 
of the different eudiometers invented to as- 
certain the purity of air by means of nitrous 
gas. The result of the numerous experi- 
ments which have been made with nitrous 
gas is, that the proportion of oxygen in atmo- 
spheric air varies in different places and at 
different times. The minimum is about 0.22, 
the maximum about 0.30 ; consequently if 
this method of analysing air is to be depend- 
ed on, we must consider that fluid not as a 
permanent chemical compound, but as a 
body subjected to all the variations to which 
accidental mixtures are liable. 
2. 'The second kind of eudiometer was pro- 
posed by Y’olta. The substance employed 
by that philosopher to separate the oxygen 
from the air was hydrogen gas. I lis method 
was, to mix given proportions of the air to be 
