Examination Procedures Goods Sold by Volume Kevin Gudmundsson Legal Metrology Advisor Trading Standards MBIE New Zealand Ben Aitken Trading Standards Officer Trading Standards MBIE New Zealand

Examination Procedures Goods Sold by Volume Samples are selected using the same procedure as if the goods were sold by mass The outcome of this examination procedure is to determine the individual package error Direct comparison This technique involves directly determining the actual quantity of the product on a graduated scale. Gravimetric Involves measuring the weight of each package and determining the volume by completing a density calculation.

Examination Procedures Goods Sold by Volume There are four methods commonly used for examining a lot of goods that are sold by volume: Direct comparison – Volumetric (destructive) Direct comparison – Template (non-destructive) Displacement bath (destructive) Gravimetric Volume (non-destructive) Direct comparison This technique involves directly determining the actual quantity of the product on a graduated scale. Displacement – determining the volume by displacing the product and measuring the volume Gravimetric - Involves measuring the weight of each package and determining the volume by completing a density calculation.

Examination Procedures Goods Sold by Volume Method 1 – Volumetric Individually opening each sample and empty all the contents into a graduated cylinder. Read error – bottom of meniscus to the top of the line

Examination Procedures Goods Sold by Volume Method 1 – Volumetric Example of test sheet Actual Quantity (mL) - Stated Quantity (mL) = Individual Package error (mL) 512 500 + 12 510 + 10 507 + 7 506 + 6 493 7 470 30

Examination Procedures Goods Sold by Volume Method 1 – Volumetric This method normally involves destroying the product as each sample package is opened and transferred to a graduated standard Method has limitations in extracting product that adheres to the internal surfaces suitable for transparent liquids, as the bottom of the meniscus is used as a datum point.

Examination Procedures Goods Sold by Volume Method 2 – Template Templates are used to determine the quantity contained in pre-packages. The individual package error is determined directly from a template associated with that packaging

Examination Procedures Goods Sold by Volume

Examination Procedures Goods Sold by Volume Method 2 – Template

Examination Procedures Goods Sold by Volume Method 2 – Basic principle It is used to measure the distance between the top of the contents in the pre-package and the upper edge of the package (the empty space) without the package having to be opened.

Examination Procedures Goods Sold by Volume Method 2 – Basic principle The template is usually marked with a graduated scale from which a direct reading from the top of the contents to the top of the container can be made. This scale is in units of volume so the volume of the fill can be directly read.

Examination Procedures Goods Sold by Volume Method 2 – Packaging requirements The packaging must be transparent. The packaging must be made of a stable material that holds its shape, e.g. glass bottles. (Any material that changes shape if a light pressure is applied will cause the level of the contents to rise or fall, and thus affect the accuracy of any measurement.)

Examination Procedures Goods Sold by Volume Method 2 – Packaging requirements The internal and external dimensions of the container must be sufficiently constant. Glass bottles are the usual containers that meet these requirements. (This can be controlled by pattern approval process or containers be verified legal metrology officials)

Examination Procedures Goods Sold by Volume Method 2 – Packaging requirements The type of cap (e.g. screw on or press on) approved for use with the bottle should be marked on the template. The template must be easily identifiable with the bottle it is approved for use with.

Examination Procedures Goods Sold by Volume Method 2 – Using the template The bottle being tested must be placed vertically on a level surface. The template is placed over the top of the bottle. Read error – bottom of meniscus to the top of the line.

Examination Procedures Goods Sold by Volume Method 3 Displacement bath Archimedes' principle The volume of displaced fluid is the volume of the object Method used to determine the volume of ice cream

Examination Procedures Goods Sold by Volume Method 3 Displacement bath

Examination Procedures Goods Sold by Volume Method 3 Displacement bath

Examination Procedures Goods Sold by Volume Method 3 Displacement bath

Examination Procedures Goods Sold by Volume Method 3 Displacement bath

Examination Procedures Goods Sold by Volume Method 3 Displacement bath Equipment: Displacement bath appropriate size for the product under test complete with a removable wire cage Ice water maintained at 1˚C to 3˚C Freezer Graduated volumetric measure Thermometer

Examination Procedures Goods Sold by Volume Method 3 Displacement bath Procedure: Products sampled are stored in a manner to ensure product integrity is maintained Place displacement bath in freezer overnight Place water in freezer until 1˚C to 3˚C is reached

Examination Procedures Goods Sold by Volume Method 3 Displacement bath Set up displacement bath and graduated cylinder on a stable level surface Fill displacement bath with water until it overflows from the spout. Wait for all visible flow to cease from the spout on the displacement bath into a tub Check water temperature is within 1˚C to 3˚C Place graduated cylinder under spout

Examination Procedures Goods Sold by Volume Method 3 Displacement bath Remove a single sample of the product from the freezer and open Remove wire mesh cage and hold above displacement bath. Place sample in cage and slowly submerge Once all visible flow has ceased from the spout on the displacement bath to graduated measure, read and record actual volume

Examination Procedures Goods Sold by Volume Method 3 Displacement bath Recheck temperature to ensure within 1˚C to 3˚C. if not, disregard result Complete steps 6 – 12 for all samples

Examination Procedures Goods Sold by Volume Method 4 Gravimetric Volume This method requires an accurate density figure to be determined The volume is determined by the following calculation volume = mass ÷ density

Examination Procedures Goods Sold by Volume Density = Mass = M Volume = V Density – A Simple Explanation Density is a measurement of how solid something is. Specifically it is the mass per unit volume of a substance. If you have two objects of the exact same size (volume), the more dense object will weigh more than the less dense object. So there are two things contributing to density: The mass of the atoms or molecules that makes up the material. The volume or amount of space the material takes up. If the molecules or atoms are “packed” in more closely, it will be more dense. For example, styrofoam or polistirean is a low density material. Even a large styrofoam container does not weigh much. The molecules in the styrofoam do not have much mass and there is a lot of space between them. A brick, on the other hand, is much more dense. Even a moderate sized brick can be pretty heavy. This is because the molecules which make up the rock have more mass and are packed more closely together.

Examination Procedures Goods Sold by Volume Table in g/mL Air = 0.0012 g/ml or 1.2 kg/m3 Gold 19.3 g/ml or 19300 kg/m3 Mayo .9 g/ml

Examination Procedures Goods Sold by Volume Method 3 – Gravimetric Example of test sheet Gross Weight (g) - ATW (g) = Actual Quantity (g) ÷ P g/mL Actual Quantity (mL) Net Quantity (mL) Individual package error (mL) 748 225 523 1.025 510 500 + 10 745 520 507 + 7 744 519 506 + 6 730 505 493 7 707 482 470 30

Examination Procedures Goods Sold by Volume Determining lot compliance for volume products Calculating the density figure

Examination Procedures Goods Sold by Volume OIML guide G 14 [Edition 2011] details a variety of methods and procedures to determine density R87 suggests a reference temperature of 20C This training session will focus on four methods Hydrometer Pycnomter Electronic Density meter Container filled with water to the brim

Hydrometer

Hydrometer Device used to determine directly the density of a liquid. It usually consists of a thin glass tube closed at both ends, with one end enlarged into a bulb that contains fine lead shot to cause the instrument to float upright in a liquid. In the glass tube is a scale so calibrated that when floating in a liquid, for which it is in the density range for, it will indicate the number of times heavier than liquid it is when read at the liquid surface

Hydrometer The function of the hydrometer is based on an Archimedes principle that a body suspended in a liquid will be buoyed up by a force equal to the weight of the liquid displaced. Thus, the lower the density of the substance, the lower the hydrometer will sink.

Hydrometer To use the hydrometer a glass cylinder with an inside diameter of at least 50 mm is required. The glass cylinder is filled with the sample. The hydrometer is lowered carefully into the sample until it floats under its own weight.

Hydrometer After the hydrometer has settled the density is read. The reading is taken on the line determined by the meniscus. If the liquid is transparent the reading is taken on the line determined by the bottom of the meniscus. If the liquid is opaque the reading is taken at the top of the meniscus.

p = reading + any correction factor. Hydrometer The density of the product is: p = reading + any correction factor. The correction factor is stated individually on the calibration certificate for each hydrometer

Hydrometer

Pycnometers

Pycnometers Pycnometers are glass or metal containers with a precisely determined volume that are used to determine the density of liquids. They are closed by a stopper or lid.

Pycnometers A density cup is a container of known volume. (V) Weigh the empty density cup and glass strike (mT). Record the result. Brim fill the density cup with product. Slide the glass strike across the brim. Ensure no air is trapped. Top up through the hole in the glass strike.

Pycnometers Carefully clean any overflowed product from the density cup and dry thoroughly. Weigh the density cup, glass strike and product to find the product weight (mL) and record the result. Calculate the density (p) p = (mL – mT) ÷ V

Pycnometers p = (mL – mT) ÷ V

Density Meters These instruments calculate the density and display it on the digital readout.

Density Meters The advantage of using these instruments is: Only a small amount of product is required to measure the density. They are easy to clean. The time taken to determine the density is very short.

Density Meters To use: Calibrate the instrument using distilled water. Insert the tube into the product and suck product into the vibrating tube. Read the density from the display

Container filled with water to the brim This method uses the product container as a pycnometer but with a strike glass as the lid. Not suitable for porous products as requires test liquid to be added to the empty space

Container filled with water to the brim The container must: not be deformable, have a flat edge, be so designed that air cannot be entrapped after complete filling.

Container filled with water to the brim Required equipment: Suitable weighing instrument Strike for the top of container Distilled water - the density is deemed 1 g/mL

Container filled with water to the brim Procedure: Allow the prepackages to stand to settle the product. Remove the lid and ensure any product that has adhered to the lid is removed and placed in the prepackage. Lightly grease the edge of container with Vaseline Ensure the control instrument reads zero. Weigh the prepackage and the strike plate and record the result on the test report (MP).

Pycnometers

Container filled with water to the brim Deliver the distilled water into the top of the product until it is almost level with the brim. Use a strike plate to ensure the prepackage is filled to the brim. Record the weight on the test report (MS). Note: If the container overfills, the test is void.

Container filled with water to the brim Determine the weight of the test liquid by subtracting the weight determined in step 6 from the weight determined in step 4. MS – MP = MSP

Container filled with water to the brim Remove all product from the prepackage and thoroughly clean and dry the empty package. Zero the weighing instrument and weigh the packing material (empty package) and the strike plate. Record the tare weight on the test report (MT). Note: lightly grease container edge

Container filled with water to the brim Fill the package to the brim with the distilled water using the strike plate. Record the gross weight of the prepackage and test liquid (MW).

Container filled with water to the brim Determine the net weight of the test liquid by subtracting the tare weight (step 10) from the gross weight (step 11). MW– MT = MWT Determine the weight of the test liquid, which substituted for the product being tested, by subtracting the weight determined in step 12 from the weight determined in step 8. Weight of test liquid = MTW - MSP

Container filled with water to the brim Determine the volume of product being tested by dividing the weight of test liquid determined in step 13 with the density of the test liquid used in step 6 & 11 (distilled water has a density of 1) Determine mass of product by subtracting MP from MT Determine the Density of the product by dividing Mass (Step 14) with the Volume (Step 15)