# ISO 1768:1975 pdf free

**ISO 1768**:1975 pdf free.Glass hydrometers一Conventional value for the thermal cubic expansion coefficient

ISO 1768 specifies,’ for use in the preparation of measurement tables for liquids, a conventional value for the thermal cubic expansion coefficient of glass hydrometers. It states how the indications of hydrometers having. a thermal cubic expansion coefficient differing from the recommended conventional value may be corrected for use in connection with measurement tables in the construction of which the conventional value has been used.

2 APPLICABILITY OF COEFFICIENT

Measurement tables for liquids provide means for deriving, from the indicatlons of density and/or relative density hydrometers at various temperatures, the corresponding value of the density and/or relative density with respect to water of the liquid at a reference temperature. In principle such measurement tables must take account of the thermal expansion of the hydrometers. Since hydrometers are made of various glasses, their expansion coefficients differ.

Consequently, it is desirable to use a single, conventional thermal cubic expansion coefficient in the construction of measurement tables and to associate with the tables information on how to adjust appropriately to the tables the indication of a hydrometer having any other thermal cubic expansion coefficient.

3 CONVENTIONAL VALUE OF COEF FICIENT

It is recommended that when preparing measurement tables for liquids the thermal cubic expansion coefficient of glass hydrometers should be taken to be 0,000 025/ C.

4 INDICATION OF COEFFICIENT USED

The thermal cubic expansion coefficient of the hydrometers, namely 0,000 025/°C，used in the construction of measurement tables for liquids shall be stated in the tables.

It shall be indicated in the measurement tables that hydrometer readings may have to be modified preparatory to using the tables if the thermal cubic expansion cofficient of the hydrometers used diffors from 0,000 025/°C

5.3 Applicability to relative density 60/60 °F hydrometers When relative density 60/60 °F hydrometers are used, it is usual to express the temperature of the liquid in degrees Fahrenheit. The modification formula quoted in 5.1 then becomes.ISO 1768 pdf download.