CHEMISTRY. 
378 
lower part of the cock E is cemented a glafs tube I I, 
which is open at the lower end near the bottom of the 
glafs. When the cock B is opened, the tubes G G, F 
E, I I, make only one fyphon; from which, when 
it is completely full, and the water in both veflels does 
not ftan'd on the fame horizontal line, the water will be 
conveyed from that veflel where it has the greateft height 
into the other, until the water in both be of the fame 
height. For example, when the water in the cylinder 
H hands at K, and in the glafs A at L, (in which cafe 
we muft fuppofe the cock D open that the air may efcape,) 
the water will continue to flow from H into A, till it 
Hands at the fame horizontal line. 
The higher the water K is railed in H, the greater is 
the weight of the column, and the quicker the efcape of 
the air. By thefe means M. Van Marum obtains what 
Melfieurs Lavoilier and Meufnier call preflure in the ga¬ 
someter, merely by the higher level of the furface K 
over L. That the height of the water in H may be ob- 
ferved, a glafs tube M M, about i-i inch in diameter, 
and connected with it, is placed between H and A, in 
which the water will always have the fame altitude as in 
H. An ivory fcale, divided into inches and lines, fattened 
to a cork ball, floats upon this water, and ferves to (hew 
the difference of the.al-titudes of the water at L and K. 
The cock N, fitted to the top of the open cylinder O, 
ferves, together with the cock P, to preferve the preflure 
perfectly uniform. Suppofe, for example, that a conftant 
preflure of water of two inches high was required; as 
much water muft be fuffered to flow continually into H, 
as is equal in bulk to the quantity of water that this pref- 
tfute of two inches forces from H into A. For this purpofe, 
fill the cylinder O, with water to the height of four inches, 
and turn the cockN, until the preflure of the four inches 
of water, which is maintained by the cock P, forces 
through N into H a quantity of water exaSHy equal to 
the quantity that the preflure of two inches forces from 
H into A. The index Q^, of the cock N, and the fcale 
R S, ferve to give to the cock N the exa< 5 l opening re¬ 
quired ; this having been determined before-hand, and 
*he fcale divided accordingly. The cock N begins to 
open when the index R is turned towards S ; and, for 
this reafon, the gradation of the fcale begins at R. When 
the index is in a vertical pofltion, the cock is completely 
open. 
As it might perhaps be difficult to give to the cock P, 
which is connefted with a ciftern of water, fuch an open¬ 
ing as not to permit more water to flow through it 
than neceflary for preferving a height of four inches 
in the cylinder O, a wafte-pipe T T is applied at this 
height, which buffers all the fuperfluous water of the cock 
P to run off. In order that it may be more conveniently 
obferved, whether the cock P has a fufficient opening 
for maintaining a four-inch column of water, a glafs tube 
U, marked at the required height, is applied on the 
.outfide, connefted with the cylinder O. 
To fill this gazometer, nothing more is neceflary than 
to let water run out from the cylinder H. For this pur¬ 
pofe, the cock V muft be opened, until the water in H 
Hands lower than that in A. The cock D, and the cock 
W, ftanding over the bell-glafs X, are then opened. The 
air contained in X rifes through the pliable tube Y Y 
into A. This filling may be continued, by leaving the 
cock V open, that the water which proceeds through the 
fyphon from A to H may run out, and the furface of 
the water in H ftand always a few inches lower than that 
in A, At the fame time the bell-glafs X is to be fup- 
plied with new gas in the ufual manner. When the ope¬ 
ration of filling is completed, the cock V is to be fhut, 
and that at Z opened ; the lower part of the opening of 
the key of which is in the fame horizontal line with zero 
of the fcale, which (hews in cubic inches the altitude of 
the water in A. By thefe means the water falls no lower 
in A, than to the above-mentioned line ; and A is con- 
fequently filled with air to the beginning of the fcale a b . 
Before the cock D is fhut, care muft be taken that the 
water in the bell-glafs X do not ftand higher than the 
water that furrounds it in its tub, which may be effected, 
if the bell-glafs be deprefl'ed in the tub, till the internal 
and external altitude of the water be perfedtly equal; 
and the air in A will then be of the fame denfity as that 
of the atmofphere. 
The gazometer is furnifhed with a thermometer f g, 
which is fo cemented with fealing-wax into a piece of 
copper e, that the bulb of it is within the gazometer. By 
thefe means the temperature of the air ufed may be 
known, and its weight accurately afcertained. The tri¬ 
pod on which the gazometer ftands, facilitates the adjuft- 
ment of the apparatus, and a brafs bottom fcrewed upon 
the tripod is furnifhed with a brafs rim or lip, to receive 
the glafs A, and keep it faft in its place. Exactly at the 
upper level of this rim the fcale a b commences. The fcale 
is of ivory, fattened on a flip of brafs, and at the ends 
are two fquare pieces of brafs, by which it is made faft, 
by means of two fcrews, to the cover at the top, and to 
the before-mentioned lip. The fcale is divided in the 
common method, by pouring equal meafures of water 
(fuppofe two cubic inches) into the glafs, and marking 
the height of each on the fcale, or, as the glafies are 
nearly cylindrical except at the neck, it may be fufficient 
to ufe at once thirty-two cubic inches, and divide the 
height into fixteen equal parts ; the neck of the veflel 
muft be divided, as above, by two cubic inches at a time. 
To explain the ufe of this gazometer, it is only necef- 
fary to fliew how the fyphon G F E I, is filled at the com¬ 
mencement of the experiment. This is done almoft in 
the fame manner in which M. Lavoifier filled the fyphon, 
which he employed in order to fill the lamp ufed in the 
experiment relpedting the comb.uftion of oil. The me¬ 
thod is as follows: The two cocks N and P are to be 
opened at the fame time, and to be kept fo until the cy¬ 
linder H is completely filled with water. The tube G G, 
which is open both above and below, as the crooked tube 
F E is not yet joined to it at F, will be filled at the fame 
time with the cylinder. The tube G G is then to be fhut. 
below by the cock h. This cock is fixed into a piece of 
brafs, which is faftened in the cylinder H by four fcrews, 
the heads of which may be feen at;, i, i, i. To this piece 
of metal, made hollow in a perpendicular direction, is 
foldered the tube G G, which touches the infide of the 
cylinder H, and is mule faft at the top by a piece of brafs, 
which is fcrewed to the interior edge of the cylinder by- 
two fcrews, the heads of which are feen at K. As loon, 
therefore, as b is fhut, the crooked tube F E is to be 
fcrewed to G G and the cock B. The cock B is fhut, the 
fcrew j is to be unfcrewed to open the tube at that place, 
and water poured by means of a funnel into the orifice 
thus opened. As foon as the tube E F is full, the orifice 
is again fhut. The cock b being then opened, and after¬ 
wards B, fo much water runs from H, through the fy¬ 
phon G F E I, that A will be completely filled, if care 
be taken, by opening the cocks N and P, that the water; 
in H ftand always higher than that in A. To liaften the 
the filling of the glafs A, 'it will be convenient to fill the 
cylinder H almoft entirely. 
In order that the bent tube E F may be faftened air¬ 
tight to the cock B, and the tube G G, without turning it 
round, each end of E F is ground to fit conically the 
places intended to receive them, and is preffed home by 
the following contrivance: Fig. 2. reprefents a fedtiou 
palling through the axis of this part of the apparatus. 
The part a a, which is furnifhed with a fhoulder, is flip¬ 
ped into the hollow c of the cock B; and the female 
fcrew dd , by means of its fhouldery f, when turned upon 
the fcrew e e, preffes the conical part a a into c. The 
conical piece of the other end F of the tube E F, is ad- 
jufted in the fame manner into a piece of copper foldered 
to the tube G G. All the tubes of this apparatus are ad- 
jufted to their refpeffive cocks in the fame manner. It 
will be luflicient to greafe flightly the furface of any of 
thefe 
