A weigh boat is a small, disposable laboratory container designed for measuring and transferring substances on a precision balance. These simple dishes accommodate small quantities of powdered solids, granular materials, or viscous liquids during the preparatory weighing process. Their use prevents chemical reagents from coming into direct contact with the delicate weighing pan of the scale. This containment ensures measurement accuracy while protecting the scientific instrument from potential contamination or corrosion.
Physical Characteristics and Primary Purpose
The design of a weigh boat is optimized for precise measurement and safe sample transfer within a laboratory setting. These containers are manufactured to be extremely lightweight, minimizing the overall mass the balance must account for and improving measurement sensitivity. Most weigh boats feature a low-profile structure and a wide, flat bottom that helps to resist accidental tipping while the sample is being added or measured.
A primary functional goal is to simplify the transfer of the measured substance once the weighing is complete. The flexible sides of most plastic boats can be easily folded to form a temporary pouring spout. This allows for the controlled dispensing of the sample into a flask or other narrow-mouthed container with minimal spillage. Using a separate container prevents the balance pan from being soiled, which extends the lifespan of the sensitive equipment and maintains the integrity of subsequent measurements.
Different Types and Materials Available
Weigh boats are available in several materials, each suited for different laboratory applications and chemical compatibilities. Polystyrene is the most common material, offering a non-reactive and inexpensive option resistant to aqueous solutions, dilute acids, and bases. These disposable plastic versions are frequently used for general-purpose weighing of most powders and granular solids.
Aluminum weigh boats provide an alternative when the sample requires exposure to high temperatures, such as in moisture content determination experiments or when working with certain organic solvents. Specialized polytetrafluoroethylene (PTFE) versions exist for handling highly corrosive chemicals. The dishes also come in various shapes, including square, diamond, and boat-shaped designs, often featuring built-in spouts or rounded corners for easier pouring control.
Essential Steps for Accurate Weighing
Achieving an accurate mass measurement begins with handling the boat correctly before it reaches the scale. Scientists should handle weigh boats exclusively using gloves or tongs to avoid transferring moisture or oils from the skin, which can add trace amounts of mass and compromise the final result.
Placement and Taring
The empty boat must be placed centrally on the balance pan to eliminate corner-load errors, which occur due to off-center placement. The next step is “taring,” which involves zeroing the electronic balance with the empty weigh boat resting on the pan. Taring ensures that the scale only measures the mass of the added substance, not the container itself.
Addressing Static Electricity
Powdered samples, particularly in low-humidity environments, can generate static electricity when placed in plastic boats, causing the material to stick to the sides and leading to a significant measurement error. To counteract these static effects, laboratories may utilize specialized anti-static weigh boats or employ an ionizer device to neutralize the charge near the balance. Increasing the air humidity can also help dissipate the charge, as moisture acts as a conductor. After the sample is weighed, the final step is a quantitative transfer, often accomplished by gently folding the boat to create a precise pouring spout.