Question

Describe the process for cleaning of redwood viscometer

Answer 1

A Redwood viscometer is another efflux type viscometer (Fig. 7.1.4-b) that works on the same principle of Saybolt viscometer. Here, the stopper is replaced with an orifice and Redwood seconds is defined for collection of 50ml of liquid to flow out of orifice. Similar expressions can be written for Redwood viscometer.

CLEANING YOUR VISCOMETERS

Clean viscometers are essential if precise and accurate measurements are to be made. Because CANNON receives a significant number of requests for advice about cleaning methods, we offer the following instructions as a guide to cleaning most glass capillary viscometers.


The first step in cleaning is to remove the bulk of the test sample. For low viscosity liquids, the viscometer may be turned upside down and allowed to hang while the test sample drains into a trough. For high viscosity liquids, the sample may have to be drawn out under vacuum. The material remaining in the viscometer must then be removed by flushing with a suitable solvent. Distilled water is an obvious choice for aqueous solutions. 
Petroleum-based lubricants and asphalts can usually be dissolved with light naphtha, heptane, octane, highly aromatic solvents, and many other petroleum-derived solvents. Varsol® is a commercial solvent that works very well for this purpose. For some types of samples it may be difficult to find a suitable solvent. 
Highly viscous samples will not easily pour from the instrument nor do they respond well even under vacuum. The best approach is to lower the viscosity by heating the instrument in an open oven or with a stream of hot air. 
Simply inverting the instrument and suspending it in an open oven over a receptacle to catch the sample usually works well. Another method is to draw the bulk of the sample out while the instrument is at an elevated temperature in a constant temperature bath. This method works particularly well for certain viscometers (such as the Zeitfuchs® Cross-Arm viscometer), as the entire cleaning can be performed while the viscometer remains fixed in the constant temperature bath. CANNON often places viscometers in an open aluminum oven (2" wide x 7" long x 5" deep), maintained at an elevated temperature, during the cleaning procedure.Even after the bulk of a viscous sample has been removed from the instrument, dissolving the rest of it may pose a considerable problem. We have found that a mixture of octane isomers is especially effective in removing the last traces of high viscosity standards from viscometers.