Volumetric wares are apparatus used for the measurement of liquid volume. They can be made from either glass or plastic wares such as pipettes, volumetric flasks, cylinders and burettes.
There are several types each having its own advantages and limitations. Pipettes are designated as class “A” or “B” according to their accuracy. Class “A” pipettes are the most accurate and the tolerance limits are well defined that is, + 0.01, + 0.02 and 0.04 ml for 2, 25, and 50 ml pipettes respectively.
Class “B” pipettes are less accurate but quite satisfactory for most general laboratory purposes. Significant errors will result if the temperature of the liquid pipetted is widely different from the temperature of calibration. The usual temperature of calibration is 20oC and this is marked on the pipette.
Burettes are used for measuring variable quantities of liquid that are used in volumetric titrations. They are made in capacities from 1to100 milliliters. They are long graduated tubes of uniform bore and are closed at the lower end by means of a glass stopper, which should be lightly greased for smooth rotation.
Conical (Erlenmeyer) flasks
Conical (Erlenmeyer) flasks are useful for titrations and also for boiling solutions when it is necessary to keep evaporation to a minimum. Some have a side arm suitable for attachment to a vacuum pump.
Flat bottomed round flasks
Flat-bottomed round flasks are convenient containers to heat liquids. A gauze mat should be interposed between the flask and flame. These flasks are widely used in the preparation of bacteriological culture media.
Round bottomed flasks
Round bottomed flasks can with stand higher temperatures than the flat- bottomed type and they may be heated in a necked flame, or in an electro- thermal mantle. They can be used for boiling of different kinds of solutions and to make titration.
Volumetric flasks are flat – bottomed, pear-shaped vessels with long narrow necks, and are fitted with ground glass stoppers. Most flasks are graduated to contain a certain volume, and these are marked with the letter “C”. Those designed to deliver a given volume are marked with the letter “D”.
A horizontal line etched round the neck denotes the stated volume of water at given temperature, for example at 20 Co .They are used to prepare various kind of solutions. The neck is narrow so that slight errors in reading the meniscus results in relatively small volumetric differences (minimizes volumetric differences or errors.)
Beakers have capacities from 5 to 5,000 ml. They are usually made up of heat resistant glass and are available in different shapes. The type most commonly used is the squat form, which is cylindrical and has a spout. There is also a tall form, usually without a spout. Beakers are often supplied for heating or boiling of solutions.
Cylinders are supplied in 10 to 2,000 ml capacities. Some are made of heat resistant glass or plastic and some are fitted with ground- glass stoppers Measurement of liquids can be made quickly with these vessels, but a high degree of accuracy is impossible because of the wide bore of the cylinders.
Test tubes are made of hardened glass or plastic materials that can withstand actions of chemicals, thermal shock and centrifugal strains. They are used to hold samples and solutions, during medical laboratory procedures. These include simple round hollow tubes conical centrifuge tubes, vacationer tubes and neck tubes.Test tubes can be with or without rims (lips). Test tubes without rim are satisfactory because there is less chance of chipping and eventual breakage.
Reagent bottles are used to store different types of laboratory reagents. They are made from glass or plastics. Depending on their use, they are available in various sizes.
Petridishes are flat glass or plastic containers, which have a number of uses in the medical laboratory. They are used predominantly for the cultivation of organisms on solid media. They are made with diameters of 5 to 14 centimeter. To isolate, identify and study the characteristics of microorganisms it is essential to grow them on artificial media, and in routine bacteriology the most important requirement of a culture medium is its ability to allow detectable growth from a minute inoculum within the shortest period of incubation.
Filter funnels are used for pouring liquids into narrow mouthed containers, and for supporting filter papers during filtration. They can be made from glass or plastic materials.
Separating funnels are used for separating immiscible liquids of different densities. Example, ether and water.