For understanding soil properties, only particles passing through which sieve are used in hydrometer analysis?

• A. # 10 sieve (2.0 mm)
• B. # 40 sieve (0.425 mm)
• C. # 60 sieve (0.25 mm)
• D. # 200 sieve (0.075 mm)

Answer: (B)

In hydrometer analysis, the primary focus is on analyzing fine-grained soils, particularly those with particles smaller than specific sizes. The purpose of using a sieve is to separate the finer particles from the coarser ones to ensure that the analysis accurately reflects the properties of the soil being tested.

The # 40 sieve, which has a mesh size of 0.425 mm, is significant because it retains larger particles that are not representative of the fines that are meant for hydrometer analysis. For hydrometer testing, the soil fraction under investigation is typically defined as the particles that pass through the # 40 sieve and specifically those that can be suspended in water for measurement of their sedimentation rate. This corresponds to the finer particles, which are critical for determining important soil characteristics such as specific gravity and particle size distribution.

Using larger sieve sizes, such as the # 10 or # 60, would not be appropriate for hydrometer analysis since they allow higher amounts of coarse material, which could skew results and reduce the accuracy of the test. The # 200 sieve, while it retains particles that are even finer than those passing through the # 40 sieve, would not be the sieve used for this analysis because it is necessary to include the size range