Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Standard Reference Materials: Tin Freezing-Point Standard - SRM 741a



Gregory F. Strouse, N P. Moiseeva


The freezing point of tin (231.928 degrees C) is a defining fixed point of the International Temperature Scale of 1990 (ITS-90). Realization of this freezing point is performed using a fixed-point cell containing high-purity ({> or =} 99.9999 % pure) tin. A 24 kg single lot of tin (99.999 97 % pure) constituting Standard Reference Material (SRM ) 741a has been evaluated, and certified as suitable for use in the realization of the freezing-point temperature of tin for the ITS-90. Based on results obtained with three fixed-point cells containing random samples of SRM 741a, the expanded uncertainty (k = 2) assigned to the freezing point temperature of the metal is 0.52 m degrees C. SRM 741a has a higher purity and a smaller expanded uncertainty (k = 2) than that of SRM 741 (originally supplied as a 350 g ingot) of 99.9999 % purity and 1 m degrees C, respectively. In this document, the methods used for the fabrication of the tin freezing-point cells and for the evaluation of SRM 741a are described.
Special Publication (NIST SP) - 260-138
Report Number


ITS-90, SPRT, SRM, Standard Reference Material, thermometric fixed point, tin freezing-point


Strouse, G. and Moiseeva, N. (1999), Standard Reference Materials: Tin Freezing-Point Standard - SRM 741a, Special Publication (NIST SP), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed June 17, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created June 1, 1999, Updated July 30, 2009