Absolute viscosity of water at 20-degrees-C

Abstract

An accurafu knowl edge of t he viscos it ies of liquids in absolute units is of fundamental importance in man y scient ifi c fi elds. Th e meas urement of t hese viscosities is almost universally based upon the absolute viscos ity of water at 20° C as a primary standard. During t he past 50 years t here has been an in creasing need for a more accurate d etermina-t ion of t his s tandard. Consequen t ly, with t he coopera tion of t he Society of Rheology and so me financial assistance from t he Chemical Foundation , this proj ect was undert aken by t he National Bureau of Standards and has now been completed. Th e determination was made by t he method of capillary fiow. By means of a calibrated i nj ector, va riou s known constan t rates of flow were prod~c e d in capillaries of m eas ured dim ensions and obser vations were made of the co rrespondmg press ure drops through t he capillari es.' Th e eff ects of t he ends of t he capillaries were r endered negligible by t he s imu ltan eo us t reatment of da ta obt ained with pairs of capi llaries having essent ia lly t he same diam eters but differen t lengths. The value found for t he viscos ity of water is 0.010019 poise as co mpared wi th 0.01005 poise, which has generally been accepted for t he past 30 years. Th e estimated accuracy o f t he !lew determination is ± 0.000003 poise. As a r es ult of this work, begin nin g 0 11 JIIly 1, 1952, the Nat ional Bureau of Standards is plannin g to use t he value 0.01002 poise for t he absolu te v iscos ity of wa:ter at 20° C a s t he basis for the calibrat ion of viscometers and standard-sample otis. It] S r eco mm end ed t hat other laboratories adopt t his value as t he primary refere nce standard for co mparative m eas urem ents of viscosity.