Burettes are specialized measuring instruments. To accurately dispense the liquid and to control the liquid outflow the burettes have attached pinch clamp, stopcock, or valve. The burettes are made out of standard, tolerant laboratory borosilicate glass to avoid breakage and cracking. We provide graduated burettes with white-enamel markings that increase visibility while using dark solutions as well as facilitate meniscus readings. A burette clamp or several three-fingered clamps are attached to the side of the burette when mounted in a vertical position as the single three-fingered clamp is likely to wobble or swing off vertically.
- Clean the burette by rinsing it with the same solution that is used for titration.
- Fill the burette above the zero mark so that there is enough liquid to prime the stopcock or rotatory valve. Remove the air bubbles from the valves.
- Pour the solution of the interest in the burette to set the zero point at eye level.
- Wipe the drops from the tip.
- Slowly open the stopcock and start the titration. Ensure that the burette tip is not touching the wall of the titration vessel. Make sure that the vessel rests on a stirrer to guarantee agitation of the titrated solution.
- Close the valve as soon as the color change of the solution has occurred.
- Read the volume of the dispensed solution.
Types of Burettes
There are four types of burettes.
- Mohr Burettes
Mohr burettes are the least accurate burettes. They do not have stopcocks at their tips; therefore flexible tubes with pinch clamps are used to control the flow of the liquid from the burette.
- Giessler Burettes
Giessler burette is commonly used in laboratory practices. It has a stopcock clamped at the tip. Some Giessler burettes have three-way stopcocks for easier filling. One way moving of the stopcock fills the burette and if it is turned 180° the burette empties.
- Automatic Burettes
For measurements, there is no arithmetic required. As they can be filled quickly and efficiently to precisely 0.00 mL, so the amount dispersed is determined simultaneously. Because of the accurate measurements, the errors due to arithmetic calculations are minimized. This type of burette is filled by intentionally overfilling the top which is enclosed and has drainage for collecting the overflow. The top portion of the automatic burette is not calibrated, so if less liquid is dispensed than is contained in this region, the amount removed cannot be determined.
- Dispensing Burette
The dispensing burette can carry up to one liter of liquid and is capable of fast and efficient liquid dispensing. Its accuracy is about ±0.5% of total volume.
Care and Use of Burettes
Burettes are more prone to chipping or cracking as they are seldom tip- or end-heat strengthened. In addition to the tip, the care of the stopcocks on a burette is equally essential. Check the stopcocks for jamming, leakage, and consistency of liquid flow. Glass stopcocks break easily so cautiously remove the plug of the burette’s stopcock, clean the plug and the barrel, and regrease it. Remove the grease from the stopcock if it is leaking and replace the plug. Tighten the plug firmly but do not rotate it.
Do not use silicon-based stopcock grease on burettes unless the nature of the chemicals requires it because silicon-based greases need constant cleaning and replacement to maintain their slippery nature. The silicon grease may be inexpensive in the short run, but the consequences are costly. Instead of the silicon grease, Teflon stopcock or rotatory valve can be used. Check the Teflon grease stopcocks for scratches periodically. Never store any solution in a burette. Alkaline solutions may react with the glass and cause freezing of the glass stopcock so never store alkaline solutions in a burette. Also, an alkaline solution may react with the glass and create a rough surface that may scratch the Teflon plug.
When filling a burette, first remove any air bubbles in the tip region. If the bubble comes out while making a measurement, it may take the place of fluid that was recorded, but never leave the burette. To remove the bubble, overfill the burette, and open the stopcock fully to push the bubble out.