ASTM E287 Standard Specification for Laboratory Glass Graduated Burets
3. General Requirements
3.1 Calibration - Burets shall be calibrated to deliver the intended volume at 20°C. No after-drainage period is allowed. Volumetric tolerances shall be within the limits specified in Table 1.
4. Design
4.1 Shape - This specification covers 10, 25, 50 and 100-mL straight burets with single-bore stopcock; 10, 25, 50 and 100-mL straight burets with 3-way stopcock; 100-mL burets with 50-mL bulb (intermediate bulb style); and 10, 25, 50 and 100-mL self-zeroing burets.
4.1.1 Self-zeroing burets shall have an ungraduated, tapered, interior extension that terminates with an overflow orifice. The exterior of the buret shall extend reasonably beyond the terminal point of the interior overflow orifice. An exterior outlet tube positioned below the overflow orifice shall also be provided for drainage of overflow. End of outlet tube shall be slightly enlarged and bulbous for attachment to flexible tubing.
4.1.2 A cross section of the graduated portion of all buret styles taken in a plane perpendicular to their longitudinal axis shall be circular.
4.2 Filling Tube - Burets may be equipped with a filling tube as described below.
4.2.1 For Class A burets, filling tubes may either be attached to the underside of a 3-way stopcock or mounted onto the lower ungraduated body of those burets having straight bore stopcocks. Filling tubes which are mounted onto the body of Class A burets must utilize a separate stopcock integral with the filling tube. When a separate stopcock is used, positioning of the stopcock must be oriented so that the handle of the stopcock plug is readily accessible when buret is in normal viewing position.
4.2.2 Filling tubes attached to 3-way stopcocks shall be in the form of an elbow, extending downward from the stopcock. The open end of the filling tube shall extend toward the rear from the buret and be slightly enlarged or bulbous for firmly securing flexible tubing.
4.2.3 Class B burets may have filling tubes affixed in any of the methods described for Class A burets or as an alternative be attached to the lower ungraduated portion of buret body without an integral stopcock.
4.3 Dimensions and Tolerances - Burets shall comply with the essential dimensions and tolerances shown in Table 1, Table 2, and Table 3.
4.4 Stopcocks - All burets shall have permanently attached stopcocks. The stopcock's handle shall be located to the right. Stopcock plugs shall be provided with a retaining device. Stopcock plugs may be either glass or TFE-fluorocarbon. All-glass stopcocks shall conform to size 2 of Specification E675. The TFE-fluorocarbon plugs shall have tapers of 1 mm for each 5 mm of length and shall conform to the requirements of Specification E911.
4.4.1 In addition, stopcocks that form a seal by having their TFE-fluorocarbon plug ends butt against a necked-down glass shell may be used, provided that a 4 mm maximum inside diameter is used for the necked-down region.
4.5 Delivery Stems - The delivery stem shall have a total length of 70 ± 5 mm, except for the 10-mL size which may have a stem 100 to 130 mm long (to comply with Test Method D664). The stem shall be permanently attached to the buret and shall be made with a gradual taper at the lower end of 20 to 30 mm. The end of the tip shall be ground perpendicular to the longitudinal axis of the tip and beveled, or it may be fire-polished instead of grinding. A sudden constriction at the orifice shall not be acceptable.
4.6 Delivery Time - The rate of outflow shall be restricted by the size of the opening in the tip, and shall be not less than the times shown in Table 2 for Class A burets and Table 3 for Class B burets.
4.7 Markings - All markings shall be permanent and legible.
4.7.1 Calibration Lines - Calibration lines shall be sharply defined and of uniform width (maximum 0.4 mm) in a plane perpendicular to the axis of the buret and parallel to each other. Lines shall be spaced at least 1 mm apart, center to center of lines. All main lines shall be numbered. Lines and numbers shall be applied by one of these methods: etched and filled with permanent pigment, by application of a stain that is fired into the glass without etching, or by application of an enamel which is fused on the glass without etching.
4.7.1.1 Class A - Least calibration lines shall extend a minimum of one half and intermediate lines at least two thirds, respectively, of the way around the outside circumference of the buret. If lines are etched, the main (numbered) lines shall extend completely around the circumference of the buret; if lines are of stain or enamel, a gap is permitted in the main lines immediately to the right of the numbers. The gap shall not exceed 4 mm for 10 and 25-mL burets, and 7 mm for 50 and 100-mL burets.
4.7.1.2 Class B - Least calibration lines shall extend a minimum of one sixth and intermediate lines at least one fourth, respectively, of the way around the outside circumference of the buret. If lines are etched, the main (numbered) lines shall extend completely around the circumference of the buret; if lines are of stain or enamel, the main lines shall extend a minimum of three fourths of the way around the outside circumference of the buret.
4.7.2 Identification Markings - Each buret, marked by one of the methods given in 4.7.1, shall show the manufacturer's name or trademark, the word "Delivers" or the equivalent symbol "TD", the temperature of calibration, that is, 20°C, and the time for unrestricted delivery of the total nominal volume. The actual delivery time may vary from the marked delivery time by ±15 s, provided the actual time is greater than the minimum given in Table 2 or Table 3.
