Manual of basic techniques for a health laboratory - libdoc.who.int

3. General laboratory procedures 773.4.3 BurettesThese are graduated glass tubes with a glass stopcock at the lower end. Burettes arefilled from the top with the liquid to be measured (Fig. 3.54). They are of 10ml,20ml, 25ml and 50ml capacity.Maintenance of burettesThe stopcock and tap should be kept well greased. To grease a clean stopcockproperly, apply the tiniest smear of petroleum or silicone jelly with a finger tipdown the two sides of the stopcock away from the capillary bore. Then insert thestopcock in the burette and rotate it until a smooth covering of the whole stopcockis obtained. Keep the top plugged or covered (Fig. 3.55).Fig. 3.55 Keep the top of the buretteplugged or coveredFig. 3.56 A graduated conicaltesting glass3.4.4 Graduated conical glasses (Fig. 3.56)These are not accurate. Avoid using them for laboratory tests.Fig. 3.54 Filling a burette3.5 Cleaning, disinfection and sterilization3.5.1 Cleaning glassware and reusable syringes and needlesInstructions for cleaning:— glass containers (Erlenmeyer flasks, beakers, test-tubes)— pipettes— microscope slides— coverslips— reusable syringes and needles.Glass containersNew glasswareGlassware that has never been used may be slightly alkaline.In order to neutralize it:● Prepare a bowl containing 3 litres of water and 60ml of concentrated hydrochloricacid (i.e. a 2% solution of acid).● Leave the new glassware completely immersed in this solution for 24 hours.● Rinse twice with ordinary water and once with demineralized water.● Dry.