'Transactions of the Bombay Geographical Society, from September 1850 to June 1852. Edited by the Secretary. Volume X.' [‎11] (30/458)

EVAPORATING DISH. x j
posing that it loses 941 grains, as indicated by the scale on the tube, to supply the amount of
one day’s evaporation : then
7158)941*0000(0-1314
715 8
I - ~
225 20
214 74
10 460
7 158
33020
2 8632
4388
So that the evaporation amounts to no inches—*1314 merely: it is seldom necessary to go
beyond the place of thousandths of an inch.
The graduations marked on a bottle which suffice for rain-gauge purposes, are scarcely
delicate enough for those of evaporation*-.for the former evaporating dish first described)
they are unserviceable altogether. The following is the method of graduation and measure
I have resorted to to secure a standard. For an unit of measure I have found the
bulb, if spindle-shaped, and part of the stem of a broken thermometer, well suited. It must
first be carefully emptied and dried—then weighed—then filled with water up to the neck
of the stem and weighed again—*as much more should now be added as gives one or two
grains more, according as the length of the stem allows: from these fill up the bulb to
where the bore becomes uniform. In a fine bored thermometer a grain will occupy an
inch in the stem, and may be subdivided by measurement into tenths or twentieths the
bulb will hold from ten to fifteen or twenty grains. All these operations are performed
before an aperture is secured in the lower part of the bulb—and marks should b e made
for say ten, fifteen, or twenty grains of water at different temperatures from 80° to 90°
those we have most commonly to deal with in India. If these experiments have been
accurately performed, the unit measure may now be carefully heated—the point of it being
approached to a lamp, and drawn out, so as to secure a capillary aperture below. If this be
well managed, the error occasioned by the bore now opened will rarely amount to the
tenth of a grain. This measure does not often require to be resorted to. The most
convenient for an unit of larger size is what is called a quill tube,—that is, a tube of glass,
about the thickness of a crow-quill, as thin in the walls as can be made : a piece a foot long at
ast should be taken, and one end of it sealed up. It should now be gauged in the manner
formerly described—if not uniform in diameter it is useless for the present purpose. The
tube is now suspended from a fine beam, and counterpoised ; fifty grains are next added and
marked, and a second fifty may be poured in to make sure—this being marked also by a
slight scratch on the tube. The spaces between the marks are now taken off by a pair of
passes, and a paper scale the length of the tube laid down on a drawing board, and very *
carefully ruled and divided. This is then gummed or pasted on, the fifty grain marks