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readings corresponding to different levels of the L. S. plunger and the different films used, thus simplifying the calculation for plant use. 1-Film
NOTES spacers are selected as previously outlined, namely: For oils of T. C. range from 120- 400 =No. 1 For oils of T. C. range from 400-1100 =No. 2 For oils of T.C. range from 1100-45OO=No. 3
The thickness is accurately determined by measuring with a micrometer to 0,0001 in., obtaining the thickness of each plate separately and then the over-all measurement. A proper selection of microscope slides is made and the spacers assembled according to Plate 111. Film plates should be marked and always kept in pairs. %To prepare I,. S . make up the following solutions: Solution A-Unfiltered cylinder stock dissolved in water-white kerosene and approximately matching a 350 Lovibond oil. Solution B-Filtered oil dissolved in kerosens to match approximately a 350 oil. Mix approximately in the proportion A : B :: 20 : 80 b y volume to obtain L. S. and in the reverse proportion to obtain the special dark standard D. S. Dilute L. S. and D. S. with kerosene until both give a reading of g.1 mm. when matched against a 50' Lovibond color glass (oil series), This 50' Lovibond glass should be carefully checked against two 25' glasses or other combination to avert any error due to an irregularity in the 50' glass. If any difficulty is experienced in matching colors from 1500 to 4600 use the D. S: (dark standard). Other standards may be made if necessary for special work and the true color value obtained by comparison with L. S. or D. S. Both L. S. and D. S . are exactly equivalent in color value, D. S. merely possessing a slightly grayer tint than L. S. which makes it easier to get a good match in some cases. For experienced observers a single standard L. S. is sufficient to cover the whole range of color determinations, 3-For oils of T. C. between 3 and 200 the 50-mm. cup is used, the
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plunger being set a t 5 , 10, 20, or 40 mm., according to the unknown oil color. For oils lighter than 3, as previously stated, the plunger is unscrewed and the oil placed in a special cell 100 mm. deep, equipped with a glass cover which fits evenly on the top and squeezes out any excess oil. 4-It is more convenient t o adjust L. S. rather than X, since in the very light oils the plunger is very near the sirface of X and permits of only a slight variation in depth. With oils where the film spacers are used L. S. is always varied; for the sake of uniformity, this procediire is recommended throughout the whole range. Calculation may also be somewhat simplified as indicated above if definite thicknesses of the unknown are always used. If any bubbles adhere t o the bottom of plunger they should be removed by tapping or by raising and lowering the plunger slightly, as these air bubbles cause errors in the color determination. 5-Any type of fastener exerting uniform pressure on the spacers may be used. Small sized paper clips are very satisfactory. Even very moderate pressure is sufficient to reduce the oil film on the spacers to an inappreciable thickness. A special type of metal holder for the film spacers has been devised which may be used with the colorimeter. By washing with gasoline the residual oil is very thoroughly and quickly removed. SOURCE OB LxcHT-Use ordinary daylight or the special daylight lamp. By using either the mirror or milked glass side of the Diiboscq reflector a t different angles the intensity of the light may be varied a t will, without any effect on the color values obtained. There is, however, a certain range in amount of light which gives the best matches without eye strain, and care should be taken not to get too much or too little light.
ACKNOWLEDGMENT The writers desire to express their appreciation for the hearty cooperation of the men on the laboratory and plant staff of the Vacuum Oil Company at Rochester, whose assistance and suggestions during the progress of this work have been invaluable.
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Simple Hydrogen Generator for Use in Making Hydrogen-Ion Concentration Measurements By Paul H. Cathcartl RESEARCHLABORATORIFS, NATIONAL CANNERS'ASSOCIATION, WASHINGTON, D. C.
HE principle involved is that of a bell jar inverted in a cylinder containing a 10 per cent sodium hydroxide solution. Two electrodes on a 110-volt D. C. circuit are introduced, the cathode within the bell jar and the anode outside and at a higher level. The outer vessel, A, consists of a large glass precipitating jar about 15 in. high, while the hydrogen reservoir is a large percolator, B, of about the same height, inverted and placed inside the precipitating jar and held about an inch from the bottom by means of glass or porcelain blocks or a porcelain acid dish, D. This slight elevation is to allow the cathode H, which is on a wire introduced through the rubber stopper C sealed in the top of the percolator, to dip slightly below the rim of the reservoir. To keep the reservoir from rising when full of hydrogen it is held down by rubber covered wires, E, fastened around the neck and running at four places down the outside of the precipitating jar and under its bottom, where they are laced together in such a way that they cannot slip off. A glass tube, G, with a stopcock passes through the rubber stopper a t the top and leads the collected hydrogen through the purifying train to the hydrogen electrode cells. The electrodes and wires which are in contact with the caustic solution are of iron and have given perfect satisfaction. The electrodes, each of about 4 sq. in. area, were stamped out of ordinary tin plate and stripped of tin with a solution of sodium plumbate (lead acetate plus an excess of sodium hydroxide), The cathode H is adjusted within the reservoir
T
1 Received
December 1, 1921.
so that it projects just below its rim, and the anode 0 is adjusted near the inside wall of the precipitating jar at such a height that it just reaches the solution when all the gas has been drawn out of the reservoir through the outlet tube. Care must be taken that the quantity of solution is not sufficient to overflow the outer vessel when the gas reservoir is full and large bubbles of excess hydrogen rise in the space between the two vessels. M represents the approximate level of NaOH solution when all the gas has been drawn out of the reservoir, and N the approximate working level of NaOH solution when the reservoir is full of gas. The generator is kept in a sink as a matter of convenience in case of overflow or breakage. An ample supply of hy- E drogen has been maintained at all times by having a lamp bank drawing a current of about 4 amp. connected in series with the electrodes. Whenever the reservoir becomes full and overflows a switch in the circuit is opened and the generation of gas is stopped until again needed. The lamps on the bank are arranged in parallel E and fastened on a board which is inverted over a small sink so that about half of the bulbs are immersed in flowing water the height of which is regulated by an overflow tube. This gets rid of both the glaring light and the heat from the lamps.
