THE VltiCOMETER

63

because as soon as a measurement has been made in one direction,
the apparatus is ready for an observation in the opposite direc-
tion. With this apparatus Pribram and Handl made very
numerous observations on organic liquids over a range of tempera-
ture. They used a constant pressure head.

The apparatus of Bruckner (1891) marked another step in
advance. He used a horizontal capillary K,
Fig. 21, connected to the two limbs of the
apparatus by means of short pieces of rubber
tubing. Two reservoirs E and R' served for
the deposition of any dust particles that might
have found their way into the liquid. The
volumes of flow were accurately measured by
the volumes of the bulbs V and V, the tubes
leading from -these bulbs being constricted

FIGV. 20.—Viscomotcr of
Pribram and Handl.

FIG. 21.—Viscometer of Bruckner.

in order to give a sharp reading. Either limb could be turned
to pressure at H or H1, or to air at Hi or H'\.
In the study of organic liquids rubber connections become
objectionable, hence Thorpe and Rodger (1894) in their monu-
mental work on the relation between the viscosity of liquids and
their chemical nature, employed an instrument, Fig. 22, similar
to that of Bruckner except that the capillary was placed inside
of a wider tube which was itself subsequently sealed to the two
limbs of the viscometer. The middle of this tube was heated at