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Date: 16-4-2017
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Date: 2-5-2017
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Date: 5-4-2016
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Burets
Burets, like measuring pipets, make it possible to deliver any volume up to the maximum capacity of the device. The precision attainable with a buret is substantially greater than the precision with a pipet. A buret consists of a calibrated tube to hold titrant plus a valve arrangement by which the flow of titrant is controlled. This valve is the principal source of difference among burets. The simplest pinchcock valve consists of a close-fitting glass bead inside a short length of rubber tubing that connects the buret and its tip (see Figure 1 a).
Only when the tubing is deformed does liquid flow past the bead. A buret equipped with a glass stopcock for a valve relies on a lubricant between the ground-glass surfaces of stopcock and barrel for a liquid-tight seal. Some solutions, notably bases, cause glass stopcocks to freeze when they are in contact with ground glass for long periods. Therefore, glass stopcocks must be thoroughly cleaned after each use. Most burets made in the last several of decades have Teflon® valves, which are unaffected by most common reagents and require no lubricant (Figure 1 b).
Figure 1 Burets: (a) glass-bead valve,
(b) Teflon valve.
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دراسة: إجراء واحد لتقليل المخاطر الجينية للوفاة المبكرة
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"الملح والماء" يمهدان الطريق لأجهزة كمبيوتر تحاكي الدماغ البشري
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المجمع العلمي يستأنف فعاليات محفل منابر النور في واسط
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برعاية العتبة العباسيّة المقدّسة فرقة العبّاس (عليه السلام) تُقيم معرضًا يوثّق انتصاراتها في قرية البشير بمحافظة كركوك
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تكريم عددٍ من عوائل الشهداء ضمن فعّاليات الحفل السنوي الثامن لذكرى تحرير قصبة البشير
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فرقة العباس (عليه السلام): تحرير قرية البشير كان بتوصيةٍ من السيد السيستاني
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