VOL.6, No. 10
ERROR IN R w m WSIGAING
1629
A POSSIBLE SOURCE OF ERROR I N RAPID WEIGHING Static electricity may be a nuisance in the chemical laboratory as well as to radio fans. I n this laboratory appreciable errors in weighing have been noted which may be accounted for by static electrical effects. In rapid weighing, when using a watch glass on the balance pan, the watch glass is dried between weighings by rubbing with a dry towel. This gives rise to a static electrical charge which may be a source of error, especially if a metal spatula is used for transfying the solid being weighed, and this spatula is not removed from the immediate vicinity of the watch glass when making a weighing. We have observed as much as nine milligrams difference in the weight of the object when the spatula is directly above the watch glass and when it is removed. Of course, this error is not created if the spatula is removed before a final balance is made. This static charge also proves to be a nuisance when weighing fluffy solids, as they are repelled from the watch glass and from each other much as pith balls repel each other when charged alike. Both of these disadvantages may be avoided by first grounding the surface of the watch glass by touching various points on the rim with the metal spatula before the solid being weighed is placed on the watch glass. These static effects are most pronounced on dry, cold days and especially if the balances are located in a dry, cool place as they are a t this institution.
