TECHNICAL INFORMATION
399
Capacities of Volumetric Ware
CAPACITY TOLERANCES FOR GLASS VOLUMETRIC APPARATUS
Many listings of Kimble® volumetric glass apparatus are designated as CLASS A, and all such glassware is permanently marked with a large A. This custom resulted from a requirement of Federal Specification DD-V-581a, Volumetric Apparatus, Glass, wherein apparatus meeting certain high requirements for accuracy was described as CLASS A and was to be marked with A. DD-V- 581a has been replaced by ASTM Specification E694 and for individual items E287 for burets; E237 and E288 for volumetric flasks; E1094 for pharmaceutical graduates; and E969 for volumetric pipets. They cover the same groups of ware, and the same requirements for accuracy and marking have been continued. The accuracy requirements are identical with those of Circular 602* of NIST, Testing of Glass Volumetric Apparatus. These various publications cover the usual burets, cylinders, volumetric flasks, volumetric pipets, and measuring pipets. In addition to these, a number of other items are held to accuracies equivalent to the values assigned by NIST to the particular items mentioned in Circular 602. Hence, the designation CLASS A has been given to many items which are not included by name or description in either the Federal Specifications or Circular 602.
MILLILITER VERSUS CUBIC CENTIMETER The Twelfth General (International) Conference on Weights and Measures redefined the liter as, “a special name for the cubic decimeter.” Thus, the relationships previously used — 1 liter = 1.000028 cubic decimeters, and 1 milliliter = 1.000028 cubic centimeters
The tolerances allowed on capacity for apparatus now designated as CLASS B are twice as large as the CLASS A tolerances.
— became void.
*NOTE: This publication is out of print but is available for loan at most Government Depository Libraries throughout the country. The new companion ASTM publications E-542 and E-694 cover what C-602 did in the past.
The Conference did agree that use of the terms “liter,” “milliliter,” and “mL” might be continued, except in association with measurements of the highest precision. Incidentally, the preferred abbreviation for cubic centimeters is “cm 3 ” — the use of “cc” is not permitted. The difference in volume between the old and the current meanings of liter is so small as to be negligible for volumetric glassware. This being so, we continue to use “liter” and “milliliter” in catalog descriptions and for inscriptions on glass apparatus. In the worst case, that of a 2000 “milliliter” flask, the difference is only 10% of the Class A tolerance.
STANDARD TEMPERATURE FOR GLASS VOLUMETRIC APPARATUS
The standard temperature in the United States and the International Standard for volumetric apparatus (ISO No. 4787) is 20 °C, and all apparatus is calibrated by manufacturers to contain or deliver the indicated capacity at this temperature unless a different temperature is specifically requested. When it is necessary in tropical countries to work at an ambient temperature considerably above 20 °C, it is recommended by the International Standards Organization that a temperature of 27 °C be adopted.
The table below illustrates this for a standard temperature of 27 °C, which is selected frequently for apparatus to be used in the tropics.
Difference in volume of glass vessels of 33 expansion borosilicate glass and 51 expansion borosilicate glass between 20 °C and 27 °C, expressed as percentage of tolerance on capacity of apparatus made to requirements of ASTM (Class A Apparatus).
Nominal Capacity
Burets
Cylinders (TD)
Volumetric Flasks
Volumetric Pipets
33 expansion borosilicate glass
51 expansion borosilicate glass
33 expansion borosilicate glass
51 expansion borosilicate glass
33 expansion borosilicate glass
51 expansion borosilicate glass
33 expansion borosilicate glass
51 expansion borosilicate glass
1
-
-
-
-
0.5%
1%
0.5%
1%
5
3.5%
5.5%
-
-
1.5%
3%
1.5%
3%
10
3.5%
5.5%
0.5%
1%
3.5%
6%
3.5%
6%
25
5.5%
9.5%
1%
1.5%
5.5%
9.5%
5.5%
9.5%
50
7%
11%
1.5%
2%
6.5%
11%
6.5%
11%
100
7%
11%
2%
3%
8.5%
14%
8.5%
14%
250
-
-
2.0%
3.5%
14%
23%
14%
23%
500
-
-
2.5%
4.5%
17%
28%
17%
28%
1000
-
-
2.5%
4.5%
22.5%
37%
22.5%
37%
2000
-
-
-
-
27%
44%
27%
44%
For similar apparatus made to Class B tolerances, the percentages are only one-half as much.
Powered by FlippingBook