APPENDIX A

311

0.1 cm (cf. page 319) reading the meniscus to 0.1 mm will give
an accuracy in the specific volume of 0.01 per cent.
CLEANING AND FILLING THE VISCOMETER
The viscometer is not removed from its frame during the course
of an investigation. Two hooks are screwed into a board on the
wall which will hold the viscometer frame firmly at E, Fig. 95.
Chromic acid, added with pipette, is drawn through the instru-
ment by means of suction. The frame and viscometer are then
again placed on hooks in an inverted position D and the liquid
withdrawn by means of suction. A Woulff flask is interposed
between the rubber tubing and the suction line. The apparatus
is washed out repeatedly with dust-free water and finally with
dust-free alcohol and dust- and grease-free ether. Air which has
passed over granulated calcium chloride A and through a long
column of absorbent cotton B is then drawn through using clean
rubber tubing.
To fill the instrument an amount of liquid slightly greater than
the working volume is drawn up into the clean pipette F which is
wiped free of dust by means of chamois skin just before use. The
liquid is protected from the moisture of the air by means of the
drying tube containing calcium chloride held in position by means
of absorbent cotton.
THE VISCOSITY RECORD
The data may be kept on sheets ruled somewhat as follows:
which will give a compact and systematic record of both data
and the calculations: