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THE JOURNAL OF INDUSTRIAL ANI) ENGINEERING CHEMISTRY
disk 7 for adjusting the length of stroke. The solution pump is adjusted to deliver 0.25 cc. and the gas pump 1.00 cc. per stroke. The pumps stroke 40 times per min. The valve t r a p on the gas side are made of capillary glass tubing (Fig. 2, 1P15) with bulbs about '/,in. inside diameter. The solution traps are of different construction, as shown in the figure. Tubes 12 and 23 are capillaries, with ends which just dip below the mercury surface 20. The absorbing liquid completely fJl8 the rest of the space in the two traps. The action of these t r a p will be clear from a glance at the drawing. The positions of the mercury columns shown in the figure are those a t the end of the suction strokes. Solution and gas have entered the cylinders by bubbling through mercury seals 20 in 1% and 17i. In the traps 160 and 170 the mercury columns have risen and sealed the outlets. On the pressure stroke, these columns fall and corresponding columns sed the inlets while the cylinders are discharged. ELECTRICAL RECORDING Srmw-The cell is made from a fitter tube of the sine to hold a No. 7 rubber stopper. The electrodes are smooth platinum, 6 mm. square, spaced 13 mm. apart. The holes in a standard No. 7 two-holed stopper are spaced about right. These electrodes are connected in series with a recording milammeter, range 0 to 50 milamperes, and about 13 dry cells. The circuit is provided with a double-pole, double-throw, knife switch, so that either the cell or 8 standard 500 ohm resistance can be placed in circuit with the ammeter. With the coil in circuit enough batteries are used to make the ammeter read 38 to 40 milamperesusually 13 new cells are neeemary. If 13 gives too high an amperage and 12 too little, used cells remedy the difficulty. After adjusting the voltage to 19 or 20 volts hy this method, the cell is put in circuit, and with 0.1 N ammonia at about 25' C., the reading should be 10 milammeters. If the gassolution ratio is now 4 to 1, each increase of 5 milamperes above 10 will correspond to 1 per cent carbon monoxide. Each dry cell lasts about a month with continuous service. An adjustment by combination of old and new cells once a week is all that is required to maintain the proper voltage.
Vol. 14, No. 11
the methane series do not necessarily interfere, because carbon monoxide can be preferentially burned to carbon dioxide. As mentioned above, use of the ratio deviceSis not restricted to gas analysis. Many other volumetric analyses, involving two or more fluids, might conceivably be performed with its aid.
Hydrogen-Ion and Other Electrical Measurements as Applied to Process Control By Ear1 A. Keeler LBBDS& N O X T ~ BCo UP ,PHILIDHLPBIII. Pn
H E INCREASING use of hydrogen-ion measurements in the industrial laboratory naturally leads one to a consideration of the possibilitiesexisting for such methods in autonmtic process control. No other electrical measurement utilized in the chemical industries possesses such an extensive and varied field for application as that of the hydrogen ion. Related as it is to the activity, or actual acidity, of solutions, it has become a factor of great importance in the control of many chemical processes. The usual chemical titration is sometimes misleading because it measures total acidity or alkalinity, thus including both free acidity and that due to salts exhibiting an acid or alkaline reaction. The hydrogen-ion concentration, or actual acidity, is frequently the predominant factor entering into reaction control.
T
PEI~FORMAWCE AND PRECISION The apparat,us as described wiU determine carbon monoxide in flue gas or in the air up to a total of 8 per cent, with an accuracy of f0.2 per cent a t temperatures around 25' C . With no temperature control on any part of the apparatus except the cell, the results should not be in error more than + 3 per cent of the amount present. The temperature coefficient of electrical conductivity being quite high, the cell must necessarily be placed in a bath. With tap water constantly running through the bath, the temperature variation from day to day is not serious but may he so from month to month. This is corrected hy occasionally changing the gas-solution ratio. The original apparatus as made from ordinary laboratory equipment ran almost continuously for six months with no skilled attention. The furnace operator took almost complete care of the apparatus, being supplied daily by the laboratory with 5 gal. of 0.1 N ammonia. The method of making this solution was simply to add 130 cc. strong reagent ammonium hydroxide to 5 gal. of distilled water. Since the original apparatus was built, two others have been constructed in much more compact form and placed in substantial wooden cabinets. APPLICATIONS
The recorder described is applicable generally for flue gas. Its sensitivity can be extended to the detection of the lower concentration of carbon monoxide encountered io mine air and in underground vehicular tunnels. Hydrocarbons of
FIG.I
The development of the hydrogen-ion automatic process control has been greatly retarded by the difficulty experienced in constructing electrode structures suitable for industrial application. Consequently, this paper is more of the nature 1 pstent
applied for.
THE JOURNAL OF INDUSTRIAL A N D ENGIPEERING CHEMISTRY
Nov , 1922
of a statement of possibilities rather than a completed report of installations in operation. Considerable improvement h a been made in the electrodes available, and kfforts are now being made to apply hydrogeu-ion control to the various processes encountered in the chemical industry. Up to the
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oil at the proper temperature for efficient distillation. Auother interesting use of electrical measuring instruments is found in the control of chemical processes by the electrolytic conductivity method. Considerable has been done along this line during the last few years. Experience has shown that, in many instances, actual control of process by automatic means is inadvisable. Fre quently there are so many variables involved that control by means entirely automatic wonld require costly and complicated apparatus. A type of process control that has been found very satisfactow under such conditions is known as the “signa-light system.’’ According to this system, signal lights of various colors are lighted when the various stages of the process are reached. The operator then uses the signals as an indication of the operations necessary and manually puts into aetiou the proper control. Signal-light control pssesses the advantages of simplicity and low maintenance cost. An interesting illustration of this type of control is involved in the electrolvtic conductivitv ecluiDment used on some of our battleships for salinity cokrol bfiresh water and boiler feed. A conductivity cell is rdaced in the distillate line from the evaporator. “he resistance of this cell is measured by a Wheatatone bridge. simal-light coutroller. which automkically lights the si&& 6mps according to the conductivity of the distilled water. The calibration of the apparatus is such that a white light is lighted if the concentration is under 0.5 of a grain of chlorine per gal. At over 0.5 of a main and under 5 erains‘ concentration a meen light is l&hted. If t,he concentration becomes excessive and above 5 grains per gal., a red light is lighted. The sigY
Pro. 2
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present time, most of the automatic control work baa been along the line of maintaining a definite hydrogen-ion comentration of boiler feed. It is well known that one of the factors entering into the corrosion of boiler steel is the hydrogenion concentration of the boiler feed. By maintenance of the feed to a concentration corresponding to a slight alkalinity, the corrosion of the boiler and its anxiliaries may be materially reduced. Fig. 1 shows a hydrogen-ion recorder controller as installed for k i e r feed control. Caustic soda is added to maintain a slight alkalinity. The water passes through a small filter and a simple air electrode operating on the aspirator principle.‘ Such an electrode is shown in section in Fig. 2. The auutornatic valve shown in Fig. 3 is motor-operated from the control circuits of the recorder controller, and opens or closes the caustic soda line leading to the feed water heaters. Another caustic soda line is bv-Dassed around the automatic valve. his line continually ?Asa small amount of alkali to take care of the minimum demand of the svstem. Variations of acidity or alkalinity result in the r&omatic valve opening or closing, thus altering the rate of alkali flow into the boiler feed. The tank and piping for handling the caustic soda solution are also shown in Fig. 3. The equipment described in this installation is practically the m e as that, required for various other applications of the hydrogen-ion automatic process control. A previous paper on this subject is of interest in that it is indicative of the possibilities existing for the application of automatic eoutml to the chemical industry.’ Other tvws of automatic urocess control utihinina electrid measuring equipment have dreads proved sueomsf$. Among P*o.3 these may be mentioned the imwrtant stwe of oil refining known & the “cracking” p m k . Here &e tempratur; recorder controller performs a useful duty in maintaining the nal lamps are placed in the evaporator room so that the operationof evaporators and the disposal of the distilled water may I’‘A Meter for Mcnsuriog Alkslinity of Boiler Feed Water,’. P-n. be controlled according to their indications. In event of a Mar 18. 1922. red lamp being lighteb the distillate is diverted into the *Tam J o u ~ & ,14 (19221. 396.
