QUANTITATIVE ANALYSIS 491 ent indication by dulling and loss of colour of the spiral.) Finally the generator is switched off. Reading the volume. The levelling bulb J is now raised on its carriage and clamped at the same level as the liquid in the graduated tube of the nitrometer. After standing for io minutes, the levels are finally adjusted and the volume of nitrogen read off with the aid of a iens. (If the meniscus is obscured by small bubbles which have collected at the gas-liquid interface, these may be dispersed as before by gently squeezing the rubber pressure tubing connecting the reservoir J with the nitrometer.) The temperature is read on the thermometer suspended from a clamp at the side of the graduated tube and the atmospheric pressure read off from an accurate barometer. Blank on tube. It is advisable with a newly packed tube to carry out a determination on A.R. glucose (ca. 25 mg.); this serves to burn out the tube by removing occluded air from the permanent filling and also as an additional
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