The last test commonly conducted test on seed lots is for purity. This separates the seed from all inert material, and seeds of other crops or weed species. The large seed sample is passed through a divider to separate it into sub-samples.
Each sub-sample is collected in a metal cup
Each sub-sample is then weighed
Reading the purity test is often a two step process. The first uses a relatively large amount of seed that passes through an automatic feeder and a shaking tray and viewed through a magnified video projector.The seed technologist views the video screen to identify seeds of other species and weeds and removes them with tweezers.
In the second step of the purity test, a small sub-sample is placed on a glass sheet with a background light.
This sample is viewed under a magnifying lens, and the sample is separated using tweezers.
Other crop seeds, weed seeds, and inert material are removed and separated.
The seeds, other crop seeds, weed seeds, and inert matter are weighed and the percentage purity is calculated.