22 NOTES ON LABORATORY MANIPULATION
Usually powdered solids are weighed in a small vial or on a piece
of paper. The object to be weighed should be placed on the left-
hand pan, the weights on the right.
- To be accurate the weights must be kept clean. Never
touch them with the hands, but use the forceps.
- When altering the load or weights, the scale pans must rest on
the floor of the balance case. Never leave the lever raised ex-
cept in taking the final swing after the weights are adjusted.
During the swing the balance door must be closed, and before it
is opened the pans must again be lowered.
- The same balance and set of weights must be used through-
out any one experiment in order that possible errors in the weights
or balances may cancel in the successive weighings.
