54 
On Hydraulic Cements. 
[Feb. 
From equation (A) we may find n when l , k, and x, are given, or in other words } 
by comparing an imperfectly filled barometer with a correct one, we may find the 
quantity of air contained in the tube, and hence find the error of indication in any 
( k — x) (/ — x) 
. - - 
other case n 
(H) . If great correctness be required, the bulk of 
the contained air, as affected by change of temperature, must be taken into account, 
but it is unnecessary to enlarge on this subject, and take up the pages of your work 
any farther, as any person who understands the previous investigation, will have no 
difficulty in applying it in any particular case. 
In all cases, however, it is preferable to have the tube perfectly freed from air, the 
surest mode of attaining which, is by boiling. But this, in the hands of an inexperi- 
enced person, is attended with great danger of cracking the tube, to avoid which, I 
shall here mention a very simple mode of making barometers nearly perfect, without 
boiling. 
Rub the tube dry with some silk tied to the end of a wire, or with a piece of 
flannel dried and heated, and then fill it with clean mercury by a paper funnel. Then 
collect all the air bubbles, excepting one or two at the top, and remove them by in- 
clining the tube. Reverse it now in a basin of mercury, and the small portion of 
air which was left in the tube, will rise to the top. Now apply the finger to the 
lower end, so as to keep it air tight, or what is better, while it is in the basin, stop 
the lower end tightly with a cork 3 . Bring the tube now into a horizontal position, 
and let the mercury run as gently as may be, to the top, and by a little care and 
management, the contained air, expanded by the diminution of pressure, may be 
brought along the tube in a large bubble, leaving the tube almost perfectly filled. 
When the bubble is brought to the end, the remainder of the tube may be filled with 
mercury, and when set up it will stand almost exactly the same as in a boiled tube. 
In this way I have filled tubes which stood to the same thousandth of an inch as 
boiled tubes ; and on some occasions I have found the mercury adhere to the top of 
the tube, and not fall till shaken. 
It is probable that a person may not succeed the first time he tries this method, 
would recommend, therefore, on first filling the tube, to pass a fine iron wire through 
e cork, to the top; then allow the mercury to fall, by withdrawing the cork in the 
basm, and then proceed as before directed, to cork the tube and bring to the 
zontal position , then by gently withdrawing the wire, the whole of the air may 
be brought along with it to the end. 
v. On Hydraulic Cements. By Lieutenant W. Saunders, Made. Eng. 
«e„ F dZe a of ri On,” f TTr 1 * ,ate 'y Conducted at Ch atham, under the superb- 
water “mlts Tl n ^ * * Ue R ° yal “pon the subject of 
equal in nualit v’t o tl R established, that artificial hydraulic mortar, nearly 
PlematerTa^ eppcyccment > b « ™de from very sim- 
a„ am " « T e “ a ' m ° St "T* ^covery, followed up by 
valuable piact,c,d investigation, with various ingredients, will prove a 
be o ™° n t0 * a ' ,d buUdere in E '™Pe, atfo it is Lly to 
rial for ml C ° nse ‘l u,!n,:e “ ““tries where the natural puzzolana, or mate- 
or making water cements, is not produced. 
"f -be tube win require to be ground smooth, and the 
P edge removed, in order that the cork may be properly inserted. 
