ISO 385 pdf download – Laboratory glassware – Burettes.
4.1 Unit of volume
The basic unit of volume shall be the millulitre (ml), which is equivalent to one cubic centimetre (cm3).
4.2 Delivery volume
Burettes shall be adjusted with water to debver their volurie (Ex), Iron, the zero line to any graduation brie, the outflow being unrestricted until approaching the final position of the meniscus. For burettes with a waiting time (Class AS). 30 s shall elapse before final setting of the meniscus.
4.3 Reference temperature
The standard reference temperature. i.e. the temperature at which the burette Is intended to deliver its nomwial volume (nominal capacity), shall be 20 C.
When the burette is required for use in a country which has adopted a standard reference temperature of 27 ‘C (the alternative recommended in ISO 384 for tropical use). this value shall be substituted for 20 C.
5 Types and classes of accuracy
5.1 Classes of accuracy
Two ciasses of accuracy are specified:
— Class A (subdivided into Classes A and AS) for the higher grade:
— Class B for the lower grade.
5.2 Types of burette
The blowing two types of burette are specified:
— that for which no waiting time is specified (Classes A and B); that for which a waiting time of 30s is specified (Class AS).
6 Maximum permissible errors
6.1 Errors in the delivered volume shall not exceed the limits given in Table 1. These limits represent the maximum permitted error at any point on the scale, and also the maximum permissible difference between the errors at any two points.
8.4 Stopcock leakage
8.4.1 A stopcock of conventional design made entirely of glass or intended for use with grease shall be tested for leakage wifh the burette clamped In a vertical position, the stopcock free from grease. the barrel and key wetted with water, and the burette filled initially to the zero line with water. The rate of leakage, with the key in either of the fully shut-off positions, shall not exceed one scale subdivision in the case of Class A or Class AS burettes or two scale subdivisions in the case of Class B burettes, in 20 mm.
Other all-glass stopcocks shall be subjected to semlar tests with their component parts free from grease and wetted with water.
8.4.2 In addition to this test, a double-bore stopcock shall not show a rate of leakage greater than that given above when tested similarty with the burette empty, the key of the stopcock in the normal delivery position and the f’illin9 tube connected to a suitable graduated tube filed with water to a level of 250 mm above the zero line of the burette.
8.4.3 lithe stopcock Is of such material that It is Intended for use without grease, it shall be tested In a
similar manner. The rate of leakage shall not exceed one-half of one scale subdivision In the case of Class A
or Class AS burettes, or one scale subdivision in the case of Class B burettes, in 50 mm,
8.4.4 For all leakage tests. in order to ensure a sufficiently accurate determination, precautions shall be taken to avoid large temperature changes (and evaporation) during the period of test
NOTE The leakage tests spedfled above are suitable for spoof cation and referee purposes. For many other purposes, a quicker test may be necessary, c which case a vacuum leakage arrangement is suitable Such a test ‘s not suitable for specification purposes owing to the difficulty of standardizing all the conditions, Any particular quick test apparatus can be calibrated by the use of several burettes whose leakage rates have been determined by means of the leakage test specified above
8.5 DelIvery Jet
8.5.1 The jet shall be made from either thick-walled capillary tiMing or a suitable inert plastic material and, if it forms an integral part of the burette, shall have no cavity at the join likely to trap air bubbles.
8.52 The jet shall be solidly manulactured with a smooth end gradual taper, without any sudden constriction at the orifice which could give rise to a turbulent outflow.
The end of the jet shall be finished by one of the following methods, ii order of preference:
a) smoothly ground with the plane of the tip at right angles to the axis, slightly bevelled on the outside and, if desired, fire-polished:
b) moulded, with me plane of the tip at right angles to the axis and slightly bevelled on the outside:
c) cut at right angles to the longitudinal axis and fire-polished.
A fire-polished finish reduces the danger of chipping In use, but should not resutt in constriction, as indicated In the first sentence of this subclause, or in undue stress, as indicated In Clause 7
8.6 Delivery time
The delivery time (see 3.2) of the burette shall be determined with water, with the stopcock fully open and with the jet not in contact with the side of the receiving vessel
The delivery time determined in this way shall be within the specified limits (see Table A 1 or B I), In the case of a detachable jet. the appropriate delivery time shall apply when the correct jet is fitted in accordance with the manufacturer’s instructions.
ISO 385 pdf download – Laboratory glassware – Burettes
