78 FLUIDITY AND PLASTICITY

the apparatus described above is unsuited. But in this case the
volume may very properly be obtained from the weight of tlie
efflux into air, because the effect of surface tension would "be

PIG. 31.—-Viscometer for gases after Schultze.
negligible at these high pressures. A viscometer designed f or"
very viscous substances is shown in Pig. 30. The use of this
form of apparatus is. described in detail in connection with
plastic flow (qf. Appendix Br p. 320).
Tfee Viscosity Measurement of Gases.—A very satisfactory
apparatus for the measurement of the viscosity of gases by the