36 CHEMISTRY. 
operations are generally constructed of glass. Their broad portion is so 
fixed as that two opposite lines, drawn from the border to the apex of the 
cone portion, shall form nearly a right angle with each other. In the 
earlier chemical manipulations special Starch were employ: ed, such as the 
one in pl. 30, fig. 48. 
Separating Funnels (pl. 30, jigs. 42 and 47) are instruments for 
separating two liquids which do not mix, and which possess different 
specific gravities, such as oil and water. The two liquids are poured 
through the upper opening into the vessel, and the latter closed air-tight by 
a well fitting stopper. The whole must be allowed to rest quietly until the 
liquids have separated into two layers. The lower aperture is then to be 
opened and the inferior layer permitted to escape. On closing the superior 
aperture with the finger the upper layer will remain in the vessel. 
Florence Flasks { pl. 30, figs. 51 and 54). The essential idea of these 
flasks consists in such an arrangement that in a tube open above and 
below, or in a flask itself, liquids may continually flow to and fro without 
the level of the liquid in the tube or flask sensibly changing. Flasks of this 
kind are used to separate a small amount of a specifically lighter body from 
a great quantity of a specifically heavier one. Thus, let water distilled over 
plants containing volatile oils flow into the tube of the flask while the lower 
end of the tube remains closed by the water in the flask; then the oil will 
constantly remain floating within the tube, the water itself entering the 
flask until it flows out of a lateral opening. In a similar way in the flask 
(fig. 51) we may collect such an oil in the neck, since the water can 
escape through the tube B. 
VII. Cuemico-Puysicat [nstruMENTSs. 
Instruments indispensable to the chemist, and which at the same time 
are used in Physics, are the barometer, the thermometer, and an accurate 
balance or pair of scales. The former instrument is sufficiently well known. 
As the thermometer is intended to determine the temperatures of very 
different substances, boiling acids, for instance, its scale must be marked 
directly onthe glass, or else be inclosed within a glass tube. The various 
forms in pl. 30, figs. 37-41, are given for the purpose of introducing 
them into the interior of other apparatus, or in order to a more ready 
support. 
Pi. 30, fig. 69, presents the most usual form of the fy sd Chemical 
Balance. The cylinder, EA, is a brass stand carrying the balance. At / is 
an eccentric disk, on turning which by the button 4, the knife-edge on 
which the beam of the balance rests when in use, may be raised to prevent 
any injury to the delicacy of its edge. Just above / there is a small plate 
of ivory, graduated to degrees, for noting the movements of the tongue FE. 
The beam of the balance is divided into ten divisions for the sake of 
weighing by tenths of small weights, constructed of platinum wire, and 
suspended from the divisions of the beam. The suspension arrangement of 
466 
