APPARATUS, ETC. 455 APPARATUS, ETC. Pipette for Calibrating Burettes, and Discussion of Principles under- lying the Calibration and Use of such Pipettes. C. W. Foulk. ( J . Ind. and Eng. Chm., 1915, 7, 689-693.)--The essential novelty consists in making the two-way stopcock the zero point of the instrument instead of having a mark on the lower stem of the pipette. The pipette itself is calibrated by weighing the quantity of water delivered by it under the same conditions as those obtaining during use.The pipette illustrated is of approxi- mately 5 C.C. capaciby, and is intended for use in cali- brating 50 C.C. burettes. The outlet orifice is constricted to small dimensions, and then filed until the pipette in a vertical position discharges itself in fifteen to sixty seconds (the specification of the Bureau of Standards for 5 C.C.pipettes). ‘The orifices of the burettes to be standardised are similarly adjusted until they comply with the speci- fication of the Bureau, which requires a burette of 50 cm. scale lengtli (about that of a 50 C.C. burette) to discharge in one and a half to three minutes. C being full, the cork is inserted, and then the tip of a filled burette.No air is thus trapped. Water is allowed to rise in F to the mark B and the water-level in the burette is adjusted to zero. The water in F is run off through the stopcock. Nine or ten pipettefuls are next run off from the burette, according as a tenth would take tho level of the water i i i the burette below the male or not. Only the final reading is needed to calibrate the pipette, but readings should be taken after each pipetteful is withdrawn, to 8456 ABSTRACTS OF CHEMICAL PAPERS make the time allowed for drainage equal to that allowed when using the pipette.Moreover, if the burette is an uncalibrated one, as it may be, this provides one set, of numbers towards the construction of a calibration curve. Suppose the reading after the ninth withdrawal 45.2 c.c., the burette is refilled to the zero mark, the pipette disconnected, and the contents of the burette down to the 45.2 C.C.mark discharged into a tared flask. From the weight of this water and its tempera- ture, its volume is calculated, and the capacity of the pipette in use is clearly one- ninth of this. The use of the pipette need not be described.I t is not worth while to expend time in trying to make it of exactly 5 C.C. capacity, but it is convenient to have it closely approximate this. G. C. J. Paraffined Apparatus for Volumetric Analyses. G. Povarnin. (J. Rim. Phgs. Chem. Soc., 1914, 46,1898-1905 ; through J. Chem. SOG., 1915,108, ii., 477-478.) -The author recommends that the measuring vessels, bottles for stock solutions, etc., used in volumetric analysis, be coated internally with a thin layer of paraffin wax.Perfectly white, crystalline paraffin wax, m.-pt. 55" C., should be employed, and, befora use, should be freed from any mechanical admixtures by fusion and decantation, or by filtration through a hot filter. The use of solutions of the wax in commercial amyl acetate, ether, or chloroform does not give good results. The ordinary dilute solutions employed in volumetric analysis are without action on the wax, and wet it very slightly indeed; this slight wetting seems to be continued by the inclusion of water by minute crystals of the paraffin wax. The general advan- tages of paraffined apparatus are that the necessity of keeping the interior of measuring vessels free from fatty matter is avoided, and that water-vapour from standard solutions does not condense on the upper parts of the vessels.Paraffined pipettes deliver completely and rapidly, and in general need not be washed out during use. Solutions of alkali hydroxide do not change in titre when stored in paraffined bottles. With iodine solutions or alcoholic alkali solutions, paraffined vessels cannot be employed.The filling of burettes is best effected from the bottom, fiince with the ordinary constant-level burettes filled from the top air-bubbles remain attached to the wttlls; this difficulty is, however, avoided by bending the delivery- tube so as to deliver the liquid against the side of the burette, and by filling the latter slowly. The correction 'for the volume occupied by the wax coating is about 0.0033 C.C.per 1 C.C. The height of the liquid, which is read at once, without waiting for the solution to drain from the walls of the burette, is determined, not by means of the meniscus, but at the line of contact of the liquid with the wax ; an accuracy of 0.01 C.C. is easily attainable, but, owing to the slight wetting of the coating, this may be diminished to about 0.02 C.C.The size of a drop is rendered far more constant by the layer of wax. It is advantageous to coat the upper two-thirds of the inner surface of the Erlenmeyer flasks used for titration. Measuring cylinders, when treated in this way, deliver their contents quantitatively. Measuring flasks should be coated over a space on each side of the mark, or, if they are to be used as pipettes, over the whole of the inner surface. Owing to the increased ease and speed with which waxed burettes and pipettes are manipulated, their use is of particular advantage in technical laboratories where large numbers of analyses are carried out.