The coefficient of viscosity (η) of a liquid is defined as the tangential force per unit area required maintaining unit velocity gradient between two successive layers of a liquid, which are unit distance apart from each other. The unit of coefficient of viscosity is dyne-sec\cm² (poise). The co-efficient of viscosity of liquid can be determined by comparing its coefficient of viscosity with the known coefficient of viscosity of a liquid. Generally, water is taken as the known liquid for comparison. As this method requires the comparison with another liquid, it is a relative method. In relative method for determination of coefficient of viscosity (η) of a liquid, Poiseuille’s equation can be used. Poiseuille’s equation

η =πPr⁴t\8vl

Where v=volume of the liquid following through a capillary tube of length (l) in ‘t’ sec. The radius of the tube is ‘r’ cm and ‘P’ is the driving pressure in dyne\cm². P can be replaced by hρg, where h= difference in height between the levels of the liquid in the two limbs, g= acceleration due to gravity and ρ is the density of the liquid. Now if the same capillary and the same volume of liquids are used, then for the two liquids the following equation can be deduced.

η₁\η₂=ρ₁t₁\ρ₂t₂

Where, ρ₁ and ρ₂ are the densities and t₁ and t₂ are time of flow for the two liquids. So, if η₂ is known, then by determining t₁ and t₂, ρ₁ and ρ₂, η₁ can be calculated.

η₁=η₂ρ₁t₁\ρ₂t₂

In the present study we are measuring the relative viscosity in comparison of viscosity of water. So as η₂ the viscosity of water and its density (ρ₂) is known (from the chart), then by measuring t₂ it’s time of flow and ρ₁, t₁ the density and time of flow of other liquids, viscosity can be calculated. Times of flow of the liquids are determined using Oswald’s viscometer and stopwatch. Densities are determined using specific gravity bottle. The flow time of the liquids are determined using Oswald’s viscometer (Fig. 1.) and stopwatch. Now η is plotted against the known concentration of sucrose that gives a straight line. From this plot the concentration of unknown solution is determined using the measured value of η of this solution.