Viscosity unit conversion: approximately how many Redwood No. 1 (Redwood I) seconds correspond to a kinematic viscosity of 1 centistoke under standard comparison conditions?

Introduction:
Legacy viscometers (Redwood, Saybolt, Engler) report efflux times rather than absolute SI units. Engineers often need quick, approximate conversions to the SI-based kinematic viscosity unit, the centistoke (cSt). This question tests recognition of the commonly used Redwood I to cSt correlation for low viscosities.

Given Data / Assumptions:

• We are relating Redwood No. 1 (a low-range efflux viscometer) seconds to kinematic viscosity in centistokes.
• The conversion is empirical and approximate, valid over typical calibration ranges.
• We specifically want the Redwood I seconds for 1 cSt.

Concept / Approach:
Empirical charts and formulas provide approximate relationships between efflux time and kinematic viscosity. For Redwood I, a commonly used approximation yields approximately 4.08 Redwood I seconds per 1 cSt at low viscosities. While exact values depend on calibration temperature and instrument, 4.08 is a widely cited round figure for quick estimates near water-like viscosities.

Step-by-Step Solution:
1) Identify the need: convert 1 cSt into an equivalent Redwood I efflux time.2) Use standard empirical correlation/lookup: 1 cSt ≈ 4.08 Redwood I seconds for low-viscosity fluids.3) Select 4.08 as the closest representative value among options.

Verification / Alternative check:
Conversion tables in older refinery and lubrication manuals list near this value for water-like viscosities; more precise work should reference the exact instrument's calibration curve.

Why Other Options Are Wrong:
1 or 0.408: Too low versus standard tables.40.8: An order of magnitude too high for 1 cSt.2.2: Not supported by typical Redwood I correlations.

Common Pitfalls:
Confusing Redwood I with Saybolt Universal or mixing up temperature bases; each instrument and temperature requires its own correlation or chart.

Final Answer:
4.08