Sample Drying Procedures. Many laboratory analyses dictate the moisture status that should be used during the analysis. If the procedure indicates that the sample should be oven dried, it must be dried for a minimum of 24 hours in 105oC oven. In order to measure the true gravimetric moisture of a sample, it is placed in an oven set to 105oC for a minimum of 24 hours, taking the appropriate weight measurements of sample and weigh tin before and after the drying process to determine the weight of the water lost. We use the silver oven on the left side of the back wall in the van Helmont room (3079G) for oven drying soils. Many processes are performed on air-dried samples. For this we weigh the sample and the labeled tin, and then place the sample in the convection cupboards located in the sieving room. The closet is just over room temperature and the forced air movement helps to dry the soils without complete cementation. Depending on the texture, air-dried soil will hold 1-12% moisture after 48 hours. After the sample is air dried, a small subsample is oven dried to calculate the gravimetric moisture content of the air dry soil. It is important to note that plants and paper bags should never be put in the soil drying oven that is set to 105⁰C. This could cause a fire and is unnecessary. The green oven in the van Helmont room is set to 35⁰C and has a convection system to maintain air movement. This helps prevent plants from growing mold. It is important to note that samples should not be packed tightly in this oven for the same reason. Additionally, there is a large drying cabinet that CAL operates in Cordley room 3052H. We also maintain around 35⁰C in these cabinets, but it is not as precise and the air flow rate is lower. However, it is ideal for large batches of samples because of the high volume capacity. The same precautions apply; do not pack samples in tightly, and make sure all samples are on a wire rack to maintain air flow.
