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SAFETY BULB FOR PIPETS THOS. S. GARDNER State Teachers' College, Johnson City, Tennessee
MANY ACCIDENTS occur in the laboratory through the use of pipets, and practically all of these could be avoided. Most pipets require concentrated attention and a momentary lapse a t a critical point invites disaster. Nearly all accidents are due to two main causes. First, too much liquid is drawn up into the pipet a t too great a rate; the liquid rises too high in the tube and enters the mouth. This is especially true if the pipet has been re-calibrated to deliver more than it ordinarily would. A second cause is inadvertently raising the tip of the pipet above the level of the liquid, causing bubbles to be drawn into the mouth. The technic of using a pipet comes only by long experience and even the best technician sometimes slips.
A small three- to five-milliliter bulb blown in the glass stem about two centimeters above the graduation mark will prevent both types of accidents. This safety trap would collect excess liquid which might otherwise be forced into the mouth. The manufacturers should make pipets of the type illustrated in A. a, A detachable safety bulb can easily be made to fit any pipet. All that is needed is a small rubber tube and a glass bulb. The over-sized dropper used in starch bottles is excellent. The bulb can be quickly fastened to any pipet and used without difficulty even by the uninitiated. (See 23.) It should always be used in pipeting strong acids and alkalies. The removable bulb is also a sanitary feature and prevents the spread of disease.
