Modified Methods of Analysis of Commercial Oil Emulsions and Suspensions FRANK M. BIFFEN AND FOSTER DEE SNELL, Foster D. Snell, Inc., 305 Washington St., Brooklyn, N. Y.
MULSIONS, good , b a d , Frequently 1 to 2 per cent of Because of the complexity of types of soap is present. Ammonia soap 1 and mediocre, are to be commercial emulsions and suspensions, is a favorite, though sodium, found in increasing numthey are classified as (1) oil emulsions free potassium, and triethanolamine bers as industrial products, and from suspended solids, (2) oil emulsions soaps are also commonly used. require methods of a n a l y s i s containing suspended solids, (3) oil soluGums, in large and small quantiwhich will be adequate to meet ties, often contribute to the statheir growing complexity and a t tions and suspensions, and (4) water-base bility of the emulsions. Wax the same time satisfactory for wax emulsions. may be present in very small reasonably general application By far the majority of commercial ina m o u n t s , in quantities not t o complex products. T h e secticides, polishes, waxes, cosmetics, etc., o r d i n a r i l y identified. Larger methods herein outlined have can be analyzed in one of these four classes amounts of wax in polishes are been developed over a period of shown by experience to dull the years in the authors' laboratory by the systematic procedures outlined. A n luster of the surface. Wax is as a result of frequent use on important advantage is that in general preoften present in relatively large c o m p l e x i n d u s t r i a1 mixtures. liminary drying to total solids is eliminated quantities in cosmetic emulsions There is no body of organized and therefore oxidative changes in properor in distinctly waxtype preparaknowledge generally applicable ties are avoided. tions, in which case a different in the literature; methods are method is used. known for such stable emulsions as milk, but do not provide for the complexity of The presence or absence of sulfonated oil should first be introduction of other ingredients such as pigments, mineral definitely established. Mix 10 cc. of the original sample oil, etc. with about 1 cc. of concentrated hydrochloric acid. Filter I n the methods commonly employed for complex mixtures, half of this. Boil the balance of the acidified samplefor afew the first step is usually to obtain the nonvolatile fraction and minutes and filter, testing the two filtrates with barium chlowork on it. I n practice this nonvolatile fraction is often far ride. The presence of a substantial amount more of sulfate from solid and rarely attains constant weight. Some part of from the boiled sample establishes the presence of sulfonated the oils present commonly evaporates more or less slowly, the oil in the sample. The blank shows the possible presence of emulsion often cracks during evaporation to give a layer of sulfate in the original sample, and may be omitted if sulfate water under a layer of oil, and as a result the oil is apt to is known to be absent. As a very small amount of sulfonated spatter during further evaporation. Any unsaturated oils oil may give no noticeable amount of sulfate precipitate by present are partially oxidized and their constants altered so this method, in special cases ash carefully with Eschka mixt h a t identification is made uncertain. ture, extract with water, and test the extract for sulfate. The modified methods proposed obviate these defects and in the majority of cases permit a complete analysis on a relaMETHOD. To 25 cc. of the sample in a narrow-necked graduated cylinder, add 0.5 cc. of concentrated hydrochloric acid. tively small sample. The methods have all been in use for an Shake thoroughly. Frequently the emulsion is broken and on extended period, and are applicable to furniture and autostanding will separate into two or more layers, the upper conmobile polishes, cosmetic emulsions, water-base waxes, and sisting of the mineral oil, the lower of the water and hydrochloric petroleum emulsions used as insecticides, to mention only a acid, and gums if present. It is usually more satisfactory to centrifuge the cylinder, when a clean-cut separation results. few examples. Any soap present is decomposed by the acid and the resulting As is so often the case, the method of analysis to be apfatty acid is in the oil layer. plied depends to a large extent on some knowledge of the comIf sulfonated oil or castor oil is present there may be three position of the sample. The classification usually requires layers, the sulfonated and saponifiable oil often forming a layer between the other oil and the water. With chlorohydrocarbon some preliminary qualitative work, unless the approximate present, the sulfonated or castor oil layer may be on the bottom, composition is already known. I n general, the products are and in any event will be easily recognized by its different color first classified in one of four groups: oil emulsions free from and consistency. suspended solids, oil emulsions containing suspended solids, Treatment in this way with hydrochloric acid does not split off any sulfate or sulfonate radical from the sulfonated oil, as oil solutions and suspensions, and water-base wax emulsions. would occur with a somewhat different procedure (S), commonly Since many well-known methods are used and the procedures used for decomposition of sulfonated oils and requiring prolonged outlined are a combination of such known methods, many refluxing with acid. details have been omitted. The amounts of the separate layers are read directly, with an accuracy depending on the type of graduated equipment used. For rapid comparison8 on products of known types, this is Oil Emulsions Free from Suspended Solids sufficient but normally more complete determinations are required. These vary somewhat in composition, although they are Separate the layers in a separatory funnel as completely as mostly white emulsions, unless artificial color has been added. possible, saving each layer. Frequently this is done on a larger sample to obtain more oil for identification, but it may be carried It is immaterial whether they are of the water-in-oil or of the out on the same sample. oil-in-water type. Mineral oil is generally present, and may Wash the oils with water and add the tvashin to the aqueous include volatile types such as turpentine substitutes. SulSeparation in the separatory funneycan be greatly fonated oil, in most cases sulfonated castor oil, may be used p."ion* acditated by immersing in a hot water bath. It is best to refrain from heating until most of the acid has been removed, thus in greatly varying amounts. Saponifiable oil may be present.
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ANALYTICAL EDITION
SEPTEMBER 15, 1935
avoiding possible hydrolysis of any sulfonated oil present. After all the water is separated, the oil fraction must be cooled, as sulfonated oil is far more soluble in mineral oil in the hot than in the cold. Sufficient amounts of the mineral oils and sulfonated or castor oil are thus obtained for the determination of constants. If the castor oil has separated, data are obtained on the oil so separated. If the saponifiable oil present proves to be miscible with the mineral oil, the determinations are more involved and it is preferable to use a modified method, described below. Obtain the saponification value of the supposed mineral oil. If it is substantially zero, get the specific gravity and viscosity as means of identification. The viscosity can be conveniently and rapidly obtained on the small amount of oil usually available by using an apparatus previously described ( I ) . If the supposed mineral oil contains saponifiable matter, obtain the acid value. A substantial acid value a t this point indicates that soap was present in the original sample. Confirm this qualitatively by adding phenolphthalein to the diluted original sample. Soaps of alkalies and ammonia have an alkaline reaction, unlike soaps of triethanolamine. If soap is present, extract a saponified portion containing excess alkali with ether to obtain a purified mineral oil for viscosity and specific gravity determinations. Saponification value, acid value, specific gravity, iodine value, refractive index, and solubility in alcohol will identify the separated saponifiable oil, which is normally castor oil, frequently of a blown grade. All these values may be obtained on 2 to 3 grams, or even less, of oil. The specific gravity is determined in a small pycnometer. Wash the oil out of the pycnometer with neutral alcohol and titrate it for acid value. After evaporating off most of the alcohol, add alcoholic potash and determine the saponification value in the usual way. The iodine value and refractive index may be obtained on less than 0.5 gram of the oil. If sulfonated oil is present, in addition to saponification value, acid value, and specific gravity, also determine the organic sulfates by the Hart-Grimshaw method (3). When only a small amount of separated sulfonated oil is available, this can be done on a portion of the original sample after neutralizing the soap and any other alkalinity present. In this case the total organic and inorganic sulfates may be precipitated with barium chloride from the water solution after the determination, giving further information as to the type of sulfonated oil. This, together with estimation of solubility in alcohol and water, is usually sufficient to identify saponifiable and/or sulfonated oil. Sulfonated oils have no very definite limits of composition, though efforts a t standardization are being made. Evaporate to dryness an aliquot of the aqueous solution from the original separation. Ammonium chloride from ammonia soap will evaporate in the oven. Loss in weight on low-temperature ashing gives the weight of gums. Boil off the excess hydrochloric acid from another portion of the aqueous acid solution and precipitate the gums with alcohol. Identify the gums so precipitated by the usual tests (4). Determine soap by direct titration of a portion of the original sample, correcting for any alkali or alkaline salts present. A good end point is nearly always obtained. Titration of the ash is misleading as, if sodium or potassium soaps are resent with sulfonated oils, a considerable part of the ash is so&m or potassium sulfate. Determine ammonia by distillation with sodium hydroxide after adding calcium chloride and triethanolamine by calculation from a Kjeldahl nitrogen determination on the original sample. The latter will occasionally require a correction because of a gumlike nitrogenous emulsifier. The amount of fatty acids liberated from the soap by the hydrochloric acid is usually too small to affect the constants of the oils materially. Allowance can be made for them if necessary when interpreting the constants. The foregoing method of separation is satisfactory in most cases. Very occasionally, however, t h e oils do not separate or the separation is not satisfactory. In that case a n alternative method is applied. ALTERNATIVE METHOD, To 16 cc. of the sam le in a 25-cc. 95 per cent narrow-necked graduated cylinder, add 8 cc. alcohol. Make distinctly alkaline with sodium hydroxide solution, shake thoroughly, and centrifuge. The mineral oil separates on top and can be read by volume; sulfonated oil goes with the alkaline alcohol and water layer. Transfer to a separatory funnel and return the alcohol-water solution to the cylinder. Wash the mineral oil with 5 cc. of 50 per cent alcohol and add the washings to the cylinder. Render the alcoholwater solution just acid with hydrochloric acid. Sulfonated
OF
317
oil, if present, separates and its volume can be read. It is not usually necessary to centrifuge. A determination of sulfates on the alcohol-water solution after liberation of the sulfonated oil and on the separated mineral oil shows ractically no sulfate present in either case. This indicates t i a t under these conditions, sulfonated oils can be treated with both sodium hydroxide and hydrochloric acid without splitting off the sulfate radical. Constants on the separated oils are determined as before. Occasionally mineral oil is found emulsified in water by a large amount of gum; the oil may be extracted with ether from the original sample and determined by methods given above.
Oil Emulsions Containing Suspended Solids Such emulsions in the main consist of a low-viscosity mineral oil, saponifiable oil, often a blown oil, and a suspended pigment or abrasive such a8 zinc or titanium oxide, diatomaceous earth, or a soft silica. They frequently contain more or less glycerol and usually an emulsifier. Gums of different types are nowadays being used more and more as emulsifiers for this type of emulsion. Small quantities of sulfonated oil and amyl acetate, oil of citronella, turpentine substitute, or other cover-odor complete the picture. Alcohol is occasionally added, together with a n y little pet ingredient that the manufacturer thinks makes his product superior to all others. METHOD. Weigh a 50- to 100-gram sample into a centrifuge bottle. Add 50 cc. of ethyl ether and shake well, but not vigorously. Very stubborn ether-water emulsions, if formed, can generally be broken by directing a small stream of alcohol from a wash bottle around the outer surface of the emulsion (8’). Separate with the centrifuge. Decant the ether and water layers into a separatory funnel, taking care that they do not become reemulsified, and return the water layer to the centrifuge bottle. Alternatively, the ether may be siphoned from the centrifuge bottle, but this is difficult without also transferring some of the water layer. Repeat the ether extraction three more times using the same procedure. Wash the combined ether extracts twice with 20-cc. portions of water and add the washings to the water in the centrifuge bottle. Transfer the ether extract to a fat-extraction flask and distill off the ether, which is conveniently recovered in an empty Soxhlet extractor. Place the fat-extraction flask and contents in the oven for the minimum time necessary to drive off the residual ether. Filtration through a paper wet with ether, before evaporation, eliminates any water which could cause spattering in the oven. The residue from the ether extract often consists of an upper layer of mineral oil and a lower layer of castor oil. To get a satisfactory separation for most practical purposes, cool the oils in ice water, adding cold ethyl ether and carefully but quickly decanting. Repeat this twice more. A little practice will enable one to make a good separation of the mineral oil from the castor oil, which if blown is ver thick when cold. Should extreme accuracy be required, use tze method of separation by means of caustic soda-alcohol-hydrochloric acid described above. Identify the mineral oil and the saponifiable oil as in the previous method. If sulfonated oil is present only as a minor ingredient, as is commonly the case in this type of emulsion, it will not seriously affect the constants of the saponifiable oil. The centrifuge bottle still contains the water solution and pigment or abrasive. Centrifuge and decant the water solution. Repeat this operation with hot water 3 to 4 times, shaking thoroughly each time. The number of times this need be repeated depends on the clarity of the last water extract. Some gums are only very slowly soluble. Combine the aqueous washings and evaporate to a small volume over a Bunsen burner. Finish on a water bath and finally in the oven until fumin just commences. Cool and weigh. This gives the combine8 weights of glycerol, gums, and any other water-soluble ingredients. Add alcohol, stir well, and heat. Filter and wash the residue of gums and any other alcohol-insoluble materials with hot alcohol. Dry in the oven and weigh on a tared filter paper. The difference is glycerol, soap if present, and any other alcoholsoluble materials. The alcohol may be evaporated and glycerol determined in the residue. Soap may be titrated in diluted solution. Dissolve the gums in water and determine their identity (4). In examining the gums, starch should be considered as in the same group. The gums and glycerol are separated individually by this method, Ether extraction of the total solids in the authors’
318
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INDUSTRIAL AND ENGINEERING CHEMISTRY
experience always carried over some of the glycerol, so that three layers were obtained from evaporation of the ether extract. There is then no simple means of knowing whether or not all of the glycerol had been carried over by the ether, in which the results indicate that it is slightly soluble. The gums remained with the pigment or abrasive and were usually determined by loss on ignition. This was not fully satisfactory, among other reasons because i t did not allow of identification. The moist pigment of abrasive remains in the centrifuge bottle, and may be dried in situ in the oven, brushed out, and weighed. The normal procedure is to make a mesh analysis, using 200- and 325-mesh sieves, and save the part meshing between these two for microscopical examination. This will at once determine whether the abrasive is a diatomaceous earth or a silica, and of what type. The pigment or abrasive may then be used for a mineral analysis if necessary. This completes the analysis using a single sample. Each of the main ingredients has been individually separated unaltered in character. Alcohol or other water-soluble solvent, if present, may be determined by the usual distillation method on another original sample.
Oil Solutions and Suspensions This type of product is not usually a true emulsion. The amount of water is very small, if present a t all. If no water is present, the product in general has no dispersed liquid phase to fall in the emulsion class. Emulsions t h a t have naphtha as a n external phase but contain a substantial amount of water are not included in this class. T h a t type, sometimes referred to as a reversed phase emulsion is classified like a similar emulsion with water as the external phase. The term "oil" is used here as a designation for any distillable fraction from petroleum, such as naphtha, gasoline, kerosene, etc., or a corresponding coal-tar fraction, such as toluene, xylene, cumene, high-flash naphtha, etc. Ammonia soap is commonly present in this type of emulsion. Other soaps are rarely employed because of their adverse effect on the consistency of the final product. Analysis of this type of product is relatively simple because of the limitations on the materials a p t to be present.
METHOD. Weigh a 100-gram sample into a distilling flask. Add solid calcium chloride in sufficient quantity to react with all the soap present. Without this addition to prevent foaming, distillation is often impossible. Determine the distillation range by the usual procedure. Care must be exercised to distill over all the oil without decomposing any compounds of fatty acids. Distillation from an oil-bath may help but usually is not necessary and it is easier, with proper manipulation, to distill the last fractions using a bare flame. Any water present, such as from aqua ammonia used in making ammonia soap, distills over with, and separates from, the oil, and its amount can be read off as a check. Ammonia if present also distills over. The amount of oil is read by volume. For very accurate work, wash the combined oil layers with water until neutral. Drain the water off and determine the specific gravity of the oil, correcting to 15.56" C. (60' F.). If desired, a straight distillation can be made on the washed oil to obtain a more accurate distillation range. Add hot dilute hydrochloric acid to the distillation flask and heat to boiling with vigorous shaking. Transfer the contents to a centrifuge bottle and wash the flask with hot water. Cool the flask and bottle and wash the flask thoroughly with ethyl ether, adding the washings to the centrifuge bottle. Proceed with the ether extraction as in the previous method. Wash the combined ether extracts with water until neutral. Evaporate the ether, place in the oven for the minimum time necessary to drive off all the ether, and weigh. This normally gives the fatty matter corresponding to the soap present in the sample, and a simple calculation gives the amount of soap. Melting point, if solid a t room temperature, acid value, and iodine value identify the source of the fatty acid. Wash the pigment or abrasive in the centrifuge bottle with
VOL. 7, NO. 5
water, again throw down with the centrifuge, and decant. Repeat this several times to remove the calcium chloride. Dr the residue in situ, brush out, and weigh. Identify by mesh analysis, microscopic examination, and, if necessary, by mineral analysis. The pigment or abrasive may also be obtained by ashing the original sample, if only a volatile soap is present. Determine ammonia by distillation into standard acid. For this add water and calcium chloride, then sodium hydroxide solution, to the sample through a dropping funnel. Subtract the amount of ammonia necessary to saponify the fatty acids from the total ammonia thus found, to give the free ammonia, if present.
Water-Base Wax Emulsions This type of emulsion is of recent importance and generally consists of a wax, such as carnauba, together with a resin such as shellac, emulsified in water with the aid of soap. Ammonia and triethanolamine soaps are preferred, though alkali soap is sometimes used. Soda soap may cause the emulsion t o become semi-solid in time. Borax is frequently present. Since wax in substantial amounts is not completely soluble in ether, the procedures previously given cannot be used and it is necessary to work on the total solids of the sample. This is not a disadvantage in this case, as no oil is present and a constant weight is readily attained without altering the characteristics of the wax and resin.
METHOD. Extract 5 to 10 grams of the total solids with carbon tetrachloride for several hours, using a Soxhlet extractor. Little advantage is obtained by using the rubber extraction type of apparatus. Rapid refluxing keeps the carbon tetrachloride surrounding the thimble in the Soxhlet tube very little below its boiling point. Recover the solvent in an empty Soxhlet apparatus, take to dryness on a water bath and finally dry to constant weight in the oven a t 110' C.. A fairly extended dr ing period is usually necessary. Lelting point, saponification value, and acid value determinations generally suffice to identify the wax. In case of doubt, iodine value, unsaponifiable matter, and aniline oint will assist. Determine the unsaponifiable matter by saponiging 5 grams of an oil low in unsaponifiable matter, such as raw castor oil, with 0.5 gram of the wax dissolved in it and extract with ether in the usual way. Correct for the unsaponifiable matter in the oil used. Alternatively, saponify the wax directly with potassium hydroxide in carbitol (6). The aniline point (5) is a recently developed constant which is particularly useful if a mixture of waxes is present, as is so often the case in commercial preparations. The determination is simple. Heat together 1 volume of wax, 1 volume of V. M. and P. naphtha, and 2 volumes of aniline in a test tube until a clear homogeneous liquid is obtained. Insert the test tube in an air bath and cool gradually by stirring with a thermometer. The aniline oint is the temperature a t which complete opacity of the liquizoccurs, and is sharp and definite. Typical values are: carnauba wax 64', beeswax 58.5", paraffin (135' F. m. p.) 93.5'. Mixtures show values intermediate between those of the waxes present. Extract the residue left in the thimble by carbon tetrachloride for several hours with hot alcohol in exactly the same way. Evaporate the alcohol. Analysis of this extract is not always simple. When alkali soap is present, titrate an aqueous aliquot, which is obtained by dissolving a weighed portion in alcohol and then diluting with a relatively large amount of water. This figure is not absolutely necessary but can be used as a check on the soap determined by titrating the ash of an original sample. Even this relatively quick method is not always simple, as borax is apt to be in the ash. Obtain the saponification value, acid value, and iodine value on the material extracted with alcohol to identify the resin present, if any. Test for rosin by the Liebermann-Storch reaction. As soap is present, it must be allowed for in interpreting the results. The identification of the alcohol extract is further complicated when ammonia and triethanolamine soaps are present. These soaps, more particularly those of ammonia, decompose in the oven. The fatty acids so liberated are extracted by the carbon tetrachloride, and this must be borne in mind when dealing with the values obtained on the wax. The soap is usually present in relatively small amount compared to the wax and consequently the wax constants other than acid value are usually not greatly altered. The alcohol extract of samples containing ammonia, and to a certain extent triethanolamine, therefore
SEPTEMBER 15, 1935
ANALYTICAL EDITION
consists largely of the resin and identification is more definite. As the number of resins used commercially is very limited, identification is usually simple. Determine ammonia on an original sample by distilling with sodium hydroxide after addition of calcium chloride to reduce foaming. The difference between the nitrogen due to the ammonia and the total nitrogen obtained by a Kjeldahl deterrnination gives the nitrogen due to triethanolamine. Obtain the borax on an original sample, preferably by the Ross-Deemer method. A quicker, though possibly less accurate method, is to titrate the carbonate and borax together on an ash of the original sample. Add glycerol and titrate the free boric acid with caustic soda. It is essential to boil off the liberated carbon dioxide after the total alkali titration. If alkali soaps are absent, the ash consists almost entirely of any borax present. Titrate directly with acid. There is always some extraneous ash from impurities in the commercial ingredients used, so that the weight of ash cannot be assumed to represent the borax content.
319
The methods given above have developed over a period of years and include suggestions from various staff members of Foster D. Snell, Inc., in particular from Cyril S. Kimball and Harry J. Hosking.
Literature Cited (1) (2) (3) (4)
Biffen, F. M., Chemist-Analyst, 22, 17 (1933). Ibid., 20, 8 (1931). Grimshaw, A. H., Textile World, 79, 1212-14, 7245 (1931). Jacobs, M. B., and Jaffe, Leon, IXD. ENG.CHEM.,Anal. Ed., 3, 210-12 (1931).
( 5 ) Katrakis, C. G., and Megaloikonornos, J. G., Praktika Akad. Athenon, 5, 267-9, 311-14 (1930). (6) Leaper, J. M., Textile Colorist, 5 5 , 601-2 (1933). REWIVEDMarch 12, 1935. Presented before the Division of Colloid Chemistry a t the 89th Meeting of the American Chemical Society, New York, N. Y., April 22 to 2 6 , 1935.
An Electronic Bridge Balance Indicator for Conductance Measurements R.
E
,. GAR3
4N AND G. F. KINNEY, Washington Square College, New Yorlc University, New York, N. Y.
LECTRON tube devices employed as alternating cur-
rent bridge balance indicators have been described by Tulauskas (8), McNamara (8), and others (1). Tulauskas’ device contains seven tubes and though McNamara’s uses but two tubes, it has the disadvantage that the balance point is not indicated directly. A single tube may be used to indicate the balance point of a n alternating current bridge, as shown in Figure 1. The Type 75 tube functions first as an amplifier, then rectifies the alternating component of the plate current, and finally indicates on the meter in the plate circuit lead the magnitude of the impressed alternating voltage.
small steady or “null-point” input potential may be balanced out by reducing the negative bias on the grid, the latter being accomplished by adjustment of R4, which has the effect of reducing the potential on the grid and diode simultaneously and in the same ratio.
This arrangement has an advantage in addition to its comparative simplicity, in that the meter reads maximum at zero impressed potential and the readings decrease as the potential is increased. Reasonable overloads normally encountered in bridge methods are therefore not harmful. The sensitivity of this device is in the order of microvolts with a primary impedance of 100 ohms, which is probably comparable t o that of untuned earphones. Since earphone This arrangement is particularly efficient because the voltage ratings are not generally given because the sensitivity varies from the bridge is first stepped up with transformer T I ,then apwith the observer and the noise level in the laboratory, close plied t o the grid of the tube, amplified, and again stepped up with comparison is not possible. Under ordinary laboratory contransformer Tz. This amplified in ut voltage is now applied between diode and cathode through t\e high resistance, Rs. The ditions-that is, without sound-proof rooms-this singlerectified pulsating current flowing across Rz produces a negative tube device is more sensitive than earphones without a voltage which is converted t o a direct current voltage by conpreamplifier and convenience of use is considerably greater. denser C1 and resistances RI and RP. This direct current voltFigure 2 is a p l i t of bridge age is then applied to the grid and its magnitude indis e t t i n g against electronic cated on the direct current i n d i c a t o r readings. The I , r 75 0-1 milliammeter in the plate balance point can easily be circuit. Thus the tube funcl o c a t e d with an accuracy tions simultaneously both as an alternating and d i r e c t of 2 parts in 100,000, which current amplifier. corresponds to a resistance This arrangement is diffimeasurement with a precult t o design, as degeneracision of *0.01 per cent and t i v e o r regenerative effects h a v e t o b e avoided. In m a y b e determined withp r a c t i c e it is best to use o u t g r a p h i n g the results. transformer Tz so that the W i t h ordinary earphones voltage on the diode will be 7 under u s u a l l a b o r a t o r y in phase with the alternating current voltage on the c o n d i t i o n s t h e apparent grid. The network RQ-R4-R6 250 dead silent region extends is used to bias the diode as over practically the entire well as the triode and the FIGURE1. DIAGRAM region shown in this plot. values are chosen to bias the RI. 1 megohm volume control TP. Interstage transformer diode suitably, in order that Since t h e r e s p o n s e of Rn Rs 1 megohm 1 w a t t Cn 0 01 mf‘d aper condenser Rz: Ra: 10,000 oh& 1 watt Si.’ 6: P. D. T.aaxIey jackswitch it may be operated a t the t h e h u m a n e a r is logaR4. 75,000-ohm 4olume control Sa. S. P. S. T. switch on R 4 point of maximum curvature Re. 6000-ohm volume control K . Kohlrausch slide wire rithmic, precision measureof the diode current-diode R7. 100-ohm potentiometer M. 0-1 milliammeter m e n t w i t h the earphones Ti. Input transformer volts curve, thus insuring e f f i c i e n t rectification. A r e q u i r e s a zero signal at
p -
-+
