June, 1925
I N D U S T R I A L A N D ENGINEERISG CHEMISTRY
By means of the following scheme an orifice setting, when once calibrated, is quickly reproduced without the aid of a gas meter. A tested capillary, which a t a given pressure will deliver a known quantity of air, discharging into atmosphere, is plugged into the outlet of the flowmeter, with the cock C open. The pressure on the capillary, then, is that of the line ahead of the flowmeter minus the orifice drop as shown by the differential scale. A mercury manometer (not shown) indicates pressures on the line. This has a soda-lime tube interposed to save the mercury from rapid oxidation by the ozone. A line pressure of 51 mm. ( 2 inches) of mercury was used in all the tests, the pressure being kept constant by use of a weighted relief valve on the blower supplying air to the ozonizer. The pressure upon the capillary when used for adjusting the orifice is thus 25 mm. (1 inch) of mercury for a full-scale reading (41 em. or 16.2 inches of oil) on the ,differential scale.
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Tests over several months' time show that the flow, for any orifice setting well up to the maximum range of the flowmeter, varies directly with the square root of the scale reading, as nearly as can be checked with a gas meter, timing with a stop watch. A setting has been made repeatedly a t different times as described by means of the fixed capillary, and the scale readings have been found very consistent. With several such tested capillaries and the calibration curves for the corresponding orifice settings a t given pressures, a large range of flow is readily commanded. The density of ozonized air (10 to 20 mg. ozone per liter) varies only slightly from that of air, and this difference is ignored. Barometer and temperature corrections were not applied, but variations in pressure will probably cause considerable error, as with any gas-measuring device. To calibrate the device with air for use with other gases, the square root of the density ratio would have to be applied.
Determination of the Density of Liquid Cast Iron' By H. A. Schwartz A-A'CIONAL MALLEABLE & STEEL CASTINGSC o . , CLEVELAND, OHIO
METHOD for the determination of the density of liquid metals, devised by Benedicks, and used by him and his eo-workers, has recently become available.* A method depending upon precisely the same principles was devised by the writer in 1921, and used in the spring of 1922 by A. F. Gorton and M. M. Austin in their laboratory, for the determination of the thermal coefficient of expansion of cast iron. The method is now described, not with any idea of questioning the originality of the distinguished Swedish investigators, but as a record of how a very similar problem was successfully attacked here without knowledge of the European experiments, and, indeed, probably before that work 'was undertaken.
A
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umn of the liquid metal having a height h 1 b&2) where a and b are the internal and external diameters, respectively, of the tube, and c is the internal diameter of the crucible. a2 The term was small; hence slight inaccuracies in b2 - ~2 measuring a, 6, and c do not visibly affect the results. Surface tension and viscosity effects should cancel out by difference, and the calculation requires no knowledge of the precise temperatures and coefficients of expansion of the several parts of the apparatus.
Method
The method depends upon measuring the change of presmire required to produce a given displacement of the surface of the metal under investigation in a tube dipping therein. The apparatus consisted of a carbon resistor furnace for melting the metal,3 a special device for determining he change of level, aspirator bottles for varying the pressure and manometers for reading it. A diagram of the essential parts, excluding the furnace and aspirator bottles, is shown i n Figure 1. A photograph of the equipment is shown in Figure 2. Molten metal a t the desired temperature and composition being contained in the crucible, the modus operandi was to produce within the system a pressure sufficient to bring the level of molten metal nearly to the bottom of the tube D. T h e distance piece C was removed, leaving the spear A hanging from the bracket B. The pressure was then slowly relieved until contact of the spear with the metal was indicated by the galvanometer. At that instant E was closed and A elevated by replacing C. The pressure was again slowly reduced, F being closed when contact was again made. The difference in pressures recorded by the manometer connected to E and F is, then, the pressure to balance a col1
Received November 21, 1924 Carnegie Scholarship Memoirs, XI11 Austin, THISJOURN.4L, 16, 156 (1924)
TO PRESSURE RLGULATION
ORMAL #VEL OF MlTlL
Figure 1
Correction for Errors
The method seems to he free from every inherent source of error, except the expansion of the spear A due to the fact that its mean temperature is greater when in its lower position than in its upper position, and the reduction of its length due to the solution of its lower end in molten iron.
The coeilicient of tiierinal expansion OS tringst,en is tively large amount of iron. If the tungaten alloy segregates 0 . 0 0 4 3 pcr 1'C. The mean temperature of the iron part of to the bottom on account of density, rendering the liquid .4 call hardly change in the limited time, oning to its distalice non-uniform, that is an advantage, as the density of t.he from t.he crucible, its considcrat~lethermal capacity, and the metal is actually determined in the upper part of the crucible lack of thermal conductivity. outside the tube. Any slight error is in the opposite direch-suming that a 3-cm. piece of tungsten wire is heat,ed tion of that due to expansion of the spear, and hence the from the temperature of its upper end to the temperature two more or less balance. of the metal---an increase of, say, l 0 0 O 0 C.-the spe:ir A Experimental elongates 1000 X 3 X 0.0000043 = 0.0129 cm. This produces a11 incrrase in / I of 0.0129/3 = 0.43 per cent, whicli is The crucible was of carbon lined with a hasic refractory, equivalent to an error in densit,y of about 0.03. Thus, the mainly magnesium aluminate. A very considerable time maximum error from this soiirrc is hsrely within our ability was required to determine the experimental procedure reto measure as thc avcragc of iiisiiy dctcrminations, xiid is quisite for good results. About twenty series of tests were made in all, the experimentation extending orer about three months and involving many disappointments. After the first ten series the final method was developed, and its adoption considerably facilitated the work. The apparatus was devised for the purpose of investigating the density, at various temperatures, of liquid iron containing mainly carbon and silicon in solution. Interest centered primarily on the field from 2 to 3.5 per cent carbon and from 0.5 to 2.5 per cent silicon. It was desired to work in a temperature range beginning as near the liquidus a s possible, and going as far as the limitations of the apparatus would permit. It was found practicable to work between about 1375" and 1500' C. Occasional difficulties were encountered, ascribed to failure of the tungsten spear to eontact properly with the metal. Since the experimenhs involved measurements on alloys varying progressively in silicon and carbon, it was easy to csst out results that appeared erratic. It is believed that the diRculties could be satisfactorily overcome by using carbon monoxide, methane, or hydrogen instead of air, and by using Flgure 2 a sensitive galvanometer and a very high external resistance much less than the error of single observations. It is proba- in order to make the contact resistance only a small fraction ble, however, that the average results are between 0.01 and of the total. 0.03 too low, since this coi-rection has not been made in these computations. General Conclusions The experiment was never begmi until the entire apparatus It is the purpose of the present paper to describe a method had come to a temperature equilibrium, so errors due to progressive expansion of the various parts are believed to have rather than to record the results of a research. It may b e well, however, to touch briefly upon certain conclusions of been excluded. The melting off of the lower end of A arnountiug to only a general application. The coefficient of expansion of liquid iron is constant at all fraction of a millimeter per contact was corrected by taking, instead of the two reddings previously decribed, three, temperatures within the experimental range tried. The five, or severi-in any case one more reading was takcn at density changes are of the order of magnitude of 0.002 gram high pressure than a t Ion. If tlie difference of pressure is per cubic centimeter per degree Centigrade. The coefficient of expansion is independent of the carbon then calculated as the difference of the averages for the two positions, it will be seeu that the mean length of A , if altered content within the limits of the experiment, but is affected by solution, is the same for both series e r e u though it varies by silicon content, an increase in silicon reducing the coefficient of expansion. The quantitati7re relations aTc somewhat throughout the series thus correcting for this source of error. The niaiiipulation was quite difficult and seemed to involve complex, however. At 1450' C., the density of the liquid i s accidental errors of considerable magnitudc. Readings taken given by the empiric equation, p = 7.16 - (0.1 Si 0.07 C), during slow changes of temperature werc never satisfactorily where silicon and carbon are taken in per cent by weight. concordant. It was accordingly determined to take a conComparison with Benedicka' Method siderahle number of scparat.e observations, usually about The writer believes that the previously described method seven at each of two temperatures, and assume that intermediate values would fall on a straight line. The latter assump- has both advantages and disadvantages, as compared with tion is doubtless not quite exact but, iii tho limited t~empera- that of Benedicks. The apparatus is much simpler, reture range studied, probably is not a source of visible error. quiring no refractories of complex form. The quartz tube, It was difficult, irr most cases, to maintain the npparatus forming the pressure member, is so nearly impervious to gases, in working condition a t temperatures above 1450" C., though except perhaps hydrogen or helium, that no noticeable leakage a few higher readings were taken. Below 1375" C.: the ap- occurs. For the writer's purpose, possible contamination of the paratus usually ceased to function, owing to the greatly increased viscosity of the molten metal as the liquidus is melts by silicon was unimportant. Alloys containing this KO useful data could be ohtaiued for lower element were handled, and the contamination was not such. annroached. .. as to prevent obtaining compositions such as were desired. temperatures. It is not believed that the small amount of tungsten dis- The displacement of the tungsten contact by an exact amount solved can have materially inrreased the density o i t h e rela- is also more precise than a reading of two variable positions.
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June, 1925
ISDCSTRIAL ALVDENGINEERING CHEMISTRY
On the other hand, Dr. Benedicks has secured chemically more inert conditions, a better opportunity for eliminating errors due to surface tension, and an opportunity of checking density a t the freezing point by independent means.
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The writer experienced difficulties with the contact points when working on high phosphorus metal, which might have been avoided by the use of the Benedicks method of protecting this part of the apparatus.
An Improved Calomel Electrode' By C . J. Schollenberger OHIOSTATEUNIVERSITY, C ~ L U M BOHIO W~.
COMPACT and nearly troubleproof calomel electrode for electrometric work is easily constructed on the plan of the sketch. The body of the electrode vessel was made from a small separatory funnel by removing the stopcock and fusing on a piece of glass tubing about 3 cm. long. The inner tube is of such diameter as to fit rather closely in this. The joint between is made tight by wrapping a strip of paper about the tube before it is forced into place. -4little paraffin melted in the tube will make it tight enough to hold mercury and prevent the escape of the potassium chloride solution. A fused glass joint would be better, but is beyond the skill of an amateur glass-worker. The ground-in plug a t the bottom is most important, and the grinding should be carefully done with fine emery and water. The ends of both plug and shell are afterwards ground down SO that they will be flush, and with the accurately ground part a t 1 the tip of the tube. When the electrode vessel is completed, the stem of the plug is cut off a t such length that when the Detud of H rubber stopper is in place it will -E exert some pressure upon the plug. A well-ground plug will permit so littledeakage that no visible diffusion-of the saturated potassium chloride is evident when the tip is immersed in a test tube of water and held to Cenhmefer Sco/e the light. Contact with the mercury of the electrode is established through a slightly bent glass tube with platinum wire fused in the end and containing a little mercury, into which the wire leading to the potentiometer is inserted. To fill the electrode vessel the space between the inner tube and d in end and partly fit$ the stem of the plug is first partly mercury, for connection to filled with saturated potassium potentiometer B-ParaBned rubber stopper, chloride, which may be drawn No. 00 or 0 Crystalline C-Approximate level of potas- up from the tip. sium chloride solution potassium chloride lis carefully D-Calomel E-Mercury placed in the inner tube from F-Joint made tight with paper above by means of a little paper and para511 &Approximate level to which tube is filled with KCI crystals SCOOP. Care should be taken H ~ G r o u n d - i n plug for liquid that the plug is not lifted in doing junction I-Glass ,,rod, about 2.5 mm. this, as a crystal2 between the diameter, with bead fused on end, and ground in t o make plug H . ground Surfaces is &&Cult t-0re-
A
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Upper end is afterwards c u t off and rounded in flame
1 Received
February 5, 1925.
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move and will cause persistent leakage. When the inner tube is filled with the crystals and liquid, a little dry filter paper is forced into the slightly flared opening above, in order to keep the calomel out of this tube. The mercury and calomel are now added, with sufficient saturated potassium chloride to fill the cell. After the calomel has settled, the filter paper is removed with forceps and the paraffined rubber stopper bearing the bent tube to establish connection with the mercury is put in place. When not in use the tip of the ground joint should be kept in water, as crystallization of the salt here may cause the joint to leak and is certain to cause diffusion potential for several minutes when the electrode is again used. The design is not novel, as a similar one is figured in the apparatus catalogs; the use of a ground-glass plug for making the liquid junction is mentioned by Lamer and Parsons,2 who state that, although diffusion potential may not be prevented, the contact is perfectly reproducible and is satisfactory in use. It has the great advantage that very little of the salt can escape into the solution under test, especially important in soil work. No separate salt bridge is necessary, as the ground tip is simply placed in the liquid under test, beside the electrode. A calomel electrode constructed as described has been satisfactory in soil work, using the quinhydrone electrode, and is considered well adapted to all electrometric titrations in which a saturated potassium chloridecalomel electrode can be used. 2
J. B i d . Chem., 67, 613 (1923).
Calendar of Meetings American Leather Chemists Association-22nd Annual Meeting, Hotel Traymore, Atlantic City, N. J., June 3 to 5, 1925. Third National Colloid Symposium-University of Minnesota, Minneapolis, Minn., June 17 t o 19, 1925. American Society for Testing Materials-28th Annual Meeting, Atlantic City, N. J., June 22 to 26, 1925. American Institute of Chemical Engineers-Providence, R. I., June 22 to 27, 1925. Joint Meeting with British Institution of Chemical Engineers, Leeds, England, July 13 to 23, 1925. National Chemical Equipment Exposition-Providence, R. I., June 22 to 27, 1925. ,American Ceramic Society-Summer Meeting, Toronto, Canada, July 4 to 11, 1925. American Chemical Society-7Oths Meeting, Los Angeles, Calif., August 3 to 8, 1925. 71st Meeting, Tulsa, Okla., April 5 to 9, 1926. American Electrochemical Society-Fall Meeting, Chattanooga, Tenn., September 24 to 26, 1925. National Exposition of Chemical Industries-New York, N. Y., September 28 to October 3 , 1925. Institute of American Meat Packers--ilnnual Meeting, Chicago, Ill., October 16 to 21, 1925.
