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380
The five animals receiving amounts of hake-liver oil varying from 0.000808 to 0.00404 gram daily recovered from vitamin A starvation and grew continuously during the 45-day experimental period. Comparing the rate of growth of the animal receiving 0.000808 gram of hake-liver oil daily with that of the animals receiving two, three, four, and five times this amount, it will be noticed that this animal did not increase its body weight quite so rapidly as those receiving the larger amounts of hake-liver oil. However, since Rat 134, which received 0.000808 gram of oil daily, grew a t a very slightly less rapid rate than the other animals, it seems fair to assume that 0.000808 gram of hake-liver oil contains nearly, if not actually, enough vitamin A to meet the needs of albino rats for growth. The tests here reported were undertaken primarily to ascertain what effect the fisherman’s habit of including hake livers with his cod livers had on the potency of cod-liver oil.
Vol. 16, No. 4
The results in this series of tests show that 0.8 mg. daily of crude hake-liver oil, carefully prepared from hake livers secured from fish in good physical condition, contains sufficient vitamin A to meet the body requirements of growing albino rats maintained on a synthetic diet lacking in vitamin A. I n the investigation of which the present study forms a part, a large number of commercial, medicinal cod-liver oils procured from a variety of sources have been tested for their vitamin A potency. The results of these tests show that a medicinal cod-liver oil which is so potent that 1 mg. daily will meet the body requirements of a growing albino rat may well be considered as having a very high vitamin A content. In view of these facts, it is evident that including hake livers with cod livers which are to be used for the manufacture of medicinal cod-liver oil does not decrease the vitamin A potency of the resulting cod-liver oil.
Analysis of Binary Mixtures’ Volumetric Turbidity Method By Charles D. Bogin COMXERCIAL SOLVENTS CORP., TERREHAUTE, IND.
Binary mixfures of two liquids, one of which has a much greater solubility in water fhan the other, are easily analyzed by titrating with water until turbid, the appearance of turbidity furnishing a sharp end point. The method can be applied to fernary mixtures if an independent method for estimating the proportion of the third subsfance is aoailabk. Solufions of salts, mixfures of organic liquids and water, and pure organic liquids can be used as tifrafing media in a similar way. The method can offen be used in the analysis of mixtures of two
liquids, bofh of which are miscible in wafer, by adding a definite volume of a third insoluble liquid and then titrating with water. I t can also be applied to mixfures of solids by dissobing them in a liquid and titrafing with a second liquid. It is useful for identificafion of pure organic substances. The percenfage of water in organic liquids can be defermined by titrating with benzene. Moisture in solids can be defermined by exfracfing it with organic liquids and determining it by a benzene tifration.
i
HE volume of water necessary to saturate a unit volume
T
of a binary mixture of two liquids, one of which has a much greater solvent action for water than the other, varies greatly with the composition of the mixture, increasing considerably with any increase in the proportion of the more water-soluble component. The attainment of saturation in such binary mixtures takes place very rapidly and smoothly, the added water dissolving instantaneously up to the very point of saturation, while at that point the addition of a minute excess of water separates the hitherto homogeneous liquid into two phases, producing an intense turbidity. This appearance of the turbidity can thus serve as an admirable end point, fully comparable in sharpness and definiteness with some of the best end points known in volumetric analysis, being a very sharp and sudden transition from a clear, transparent liquid to a turbid emulsion and produced by the addition of as little as the one last drop of water. The volume of water that can be added to a unit volume of a binary mixture of any certain composition before turbidity appears is very definite and invariable, absolutely independent of the time of contact, amount of shaking, or speed of addition, and only slightly dependent on the temperature, while the technic involved is that of ordinary volumetric analysis. The measurement of the volume of water used, therefore, offers great possibilities for a quick and accurate determination of 1
Received November 13, 1923.
the composition of binary and, under certain conditions, ternary mixtures. The turbidity end point has been used considerably by physical chemists for determining the solubility relations of liquid mixtures, such as the volume of water that will dissolve in various mixtures of ethyl alcohol and benzene, and the simplicity and accuracy of the method have been very favorably commented upon.2 The use of the solubility data thus obtained for the identification and analysis of unknown mixtures of the same materials, however, has not received the attention that it deserves. A method employing a turbidity end point has been suggested for the analysis of aqueous solutions of ethyl alcohol by Dubaux and Dutoit3 and others. I n those methods the critical solution temperature of mixtures containing definite proportions of the sample and certain reagents is used to determine the percentage of ethyl alcohol in the sample. The writer has been using several modifications of the turbidity method for the analysis of mixtures of ethyl and butyl alcohols, as well as mixtures of the two alcohols together with acetone, for which analysis in connection with the Weizmann fermentation process the turbidity method has been developed. These methods will be described in detail.
* Seidell, “Solubilities,” 2nd ed., p. 776. 8
Ann. chim. anal., 13, 4 (1908).
April, 1924
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
ANALYSISOF ETHYL-BUTYL MIXTURES
381
small drop of water at the end is sufficient to produce a very heavy turbidity in the formerly clear liquid. The known methods of analyzing mixtures of two alcohols, The method is most accurate for mixtures containing 25 to such as ethyl and amyl alcohols, are based mainly on the 50 per cent of ethyl alcohol, as for these proportions the curve different solubility of the two alcohols in salt solution on one is steep. I n such mixtures, using a 20-cc. sample for a dehand, and in organic solvents, as carbon disulfide, carbon termination, each per cent difference in the proportion of tetrachloride, or petroleum ether, on the other hand. I n ethyl alcohol corresponds t o a difference of 1.7 cc. in the this wtiy, by repeated extraction with the solvents and wash- volume of water required, so that results accurate to within ing of the extract with salt solution, a separation of the two 0.05 per cent can easily be obtained. As the percentage of alcohols is achieved. Such are the methods of H ~ l m e s , ~ethyl alcohol approaches close to 50 per cent, the sharpness of the end point decreases somewhat, but this is made up for by the increase in the volume of water, which corresponds to a unit difference in the proportion of ethyl alcohol. This increase is well shown by a change in the slope of the curve, which at this point becomes almost vertical. When the proportion of ethyl alcohol is less than 25 per cent, the curve inclines more to the horizontal, so that the results are less accurate. On the other hand, when the proportion of ethyl alcohol goes above 52 per cent, the mixture becomes miscible with water in all proportions and the method is not applicable directly. However, the turbidity method is adapted to such low ethyl and high ethyl mixtures by adding to the sample a carefully measured volume of either ethyl or butyl alcohols sufficient to bring its composition within the favorable 25 to 50 per cent range. I n this way the method is made applicable to all possible mixtures of ethyl and butyl alcohols from 0 u p to 100 per cent, and can even be used for detection of traces of either alcohol in the other one. EFFECT OF TEMPERATURE-AS is seen from the two curves I I I I I J for 20” and 30” C., the effect of the temperature is too large 0 IO 20 30 40 50 60 70 60 90 % of EfhylAfcohol to be disregarded in accurate work, though it is of slightly F I G . 1-MIXTURES OR ETHYL AND BUTYL ALCOHOLS TITRATED U P TO less importance than in specific gravity and index of refracAPPEARANCE O F TURBIDITY tion measurements. The effect of 10” C. is equal, on the Curve A-Titrated with water at 30’ C.; Curve B-Titrated with water average, to that of a difference of 2 5 per cent ethyl alcohol. with 5 per cent sodium chloride solution a t 20° C.; Curve C-Titrated By measuring the temperature of the emulsion immediately with 20 per cent sodium chloride solution a t 24” C.; Curve D-Titrated a t 24O C. after the titration is completed and interpolating between the two curves, the temperature factor is easily taken care of. Al1en-n’larquardtl6 and Bardy.6 These methods, however, EFFECT OF SHAKING are not of great accuracy, even in case of amyl alcohol, owing -It has been noticed to the fact that part of the amyl alcohol is lost in the salt solution, while the ethyl alcohol is somewhat soluble in the several times, espe/OD organic solvents used for extraction. This necessitates the cially with mixtures of application of various corrections to the result, as the one ethyl alcohol and benobtained by a combination of the specific gravity and the zene described later, refraction values which is used in the Holmes method. I n that vigorous shaking e the case of butyl alcohol the effect of this imperfect separation s o m e t i m e s has the $ of the two alcohols is still more pronounced. Thus, it was effect of destroying the 2 BO shown by Bedford and Jenks’ that only 30 to 70 per cent of emulsion and necessi- cI butyl alcohol present in ethyl alcohol is determined by the tating the addition of $ ?o Allen-Marquardt method, mainly as a result of the imperfect more water. It was separation of the two alcohols. These methods are also very firmly e s t a b l i s h e d , ,” laborious, involving several extractions and some distillations, h o w e v e r , that this ~ 6 0 and the incidental mechanical losses are considerable. To effect of shaking is only % , supply the need for a quick and more accurate method for apparent and is really analyzing such mixtures, the turbidity method has been due entirely to the rise in temperature that developed, which is performed in the following way: 40 METHOD-A sample (10 or 20 cc.) of the mixture which follows such shaking. % of P f h y l Alcohol On cooling the clarified has been dried over potassium carbonate is pipetted into a down to the F I G . MIXTURES OF ETHYLAND BUTYL flask and water added from a buret until the liquid becomes liquid pxe,ct, t,pmnpref11rp TITRATED WITH’I W A T E R U P TO ____. nt, -_ ALCOHOLS turbid. The temperature of the resulting emulsion is im- which bhe titration was COMPLET* DISAPPEARANCE OF TURBIDITY Curve A-Titrated with water a t 20° C.; mediately taken and the percentage of ethyl alcohol corresponding to the volume of water used is read off from Curves finished, the turbidity Curve B-Titrated with water at 30° C. A and B, Fig. 1, interpolating between the two curves for reappears. As was menJioned before, the end point is very sharp, a the temperature correction. The end point is very sharp and results can easily be obtained within 0.05 cc., as one strong turbidity resulting from the addition of the last drop of water to the previously clear liquid. This turbidity is 4 Siinmonds, “Alcohol, Its Production, Properties, a n d Application,”:p. evidently not due to the dispersion of the single drop of ex402. cess water in the large volume of liquid. This in itself could 6 Allen, “Commercial Organic Analysis,” Vol. 1, 1909,:~. 188. produce only a very faint cloudiness. What does take place 8 Simmons, LOC.c d . , p. 417. is, that as soon as the minute excess of water is added, the 2 J. SOC.Chem. I n d . , 26, 123 (1907). =--I-----
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formerly homogeneous liquid divides into two phases, which ultimately separate into two layers, a lower one consisting of a solution of the alcohols in water and an upper one which is a solution of water in the alcohols. These two layers vary in their proportion with the variation in the proportions of the two alcohols, as shown in Table I. Within the favorable range of 25 to 50 per cent ethyl alcohol the smaller layer is never less than 6 per cent and often approaches 50 per cent. The intimate mixture of these two large volumes of liquid produces an intense turbidity which defines the end point very sharply. TABLEI-LIQUID
I N UPPER LAYER CORRESPONDING TO
ORIOINALMIXTURE Per cent Per cent Ethyl Alcohol Upper Layer 94 21 92 23 89 31 64 36 42 25 43 11 50 6 (These figures are only approximately correct.)
FIG.3-MIXTURES
OF
% of Ethyl Alcohol ACETONE,ETHYL ALCOHOLA N D TITRATED WITH WATER
ETHYL ALCOHOLI N
BUTYL
ALCOHOL
TITRATION WITH SOLUTIONS OF SALT-A method has been outlined above for analyzing mixtures containing more than 53 per cent of ethyl alcohol, which consists of adding carefully measured quantities of butyl alcohol to the mixture to bring it within the 25 to 50 per cent range. Another method is to substitute solutions of salts for those of pure water as the titrating liquid. Thus, a solution of 5 per cent sodium chloride was used for Curve C, Fig. 1, with ti favorable range of 40 to 60 per cent of ethyl alcohol, while a 20 per cent sodium chloride solution gave Curve D , Fig. 1,with a favorable range of 70 to 85 per cent. The end point in Curve C is as distinct as when using water, but Curve D is not quite so good, mainly because the high specific gravity of the salt solution and possibly the high concentration of electrolytes break up the emulsion more rapidly and separate the two phases into layers very early. The first method outlined, that of adding
. Vol. 16, No. 4
butyl alcohol to the solution, has the advantage that pure water is the titrating medium and need not be standardized. Still, if mixtures containing 50 t o 80 per cent of ethyl alcohol are to be analyzed as a matter of routine, the use of salt solutions offers certain advantages. I n a similar way, by using various mixtures of water and the two alcohols as the titrating liquid, other favorable ranges can be obtained. The writer hopes to develop a series of such mixtures covering all mixtures of ethyl-butyl from 0 t o 100 per cent. DISAPPEARANCE OF TURBIDITY AS EKDPOINT-A different$ method of titration forms the basis for the curves in Fig. 2. These curves show the volume of water required to saturate a unit volume of the sample and then redissolve the emulsion and clarify the liquid. They are, therefore, merely curves of the solubility of the various alcohol mixtures in water. The end point is far less definite than in the preceding curves, as is to be expected since the conditions here are similar to the solution of a single liquid in water and the reasons that make the end point in the other curves so sharp are absent, Thus, the end point is not the sudden appearance of an emulsion resulting from the separation into phases, but the disappearance of one of the phases by solution, which, like any other case of forming a saturated solution, is far more gradual. The method might be of use as a check on the results obtained from Curve 3. in cases where the presence of foreign substances is suspected, since the effect of those substances on the curves of Fig. 1 and 2 might be different and their presence detected by the discrepancy between the results. Curves C and D, Fig. 1, might also find some use for the same purpose. The interesting fact will also be noticed that the temperature factor for the curves in Fig. 2 is positivethat is, it takes more water to dissolve a unit volume of the mixture at 30" C. than at 20' C., which is contrary to expectations. ANALYSIS OF TERKARY MIXTURES The methods described above are, of course, applicable only when the absence of appreciable quantities of foreign substances in the sample is assured, since the presence of almost any other organic liquid will affect the results one way or other, depending on its solubility relations with respect to water. However, if the amount of the third substance can be determined by an independent analysis and allowed for, the turbidity method becomes fully applicable. Such a mixture is one of the two alcohols plus acetone, which the w r i t e r is frequently 25 called upon to analyze. I n the analysis of such mixtures the per- y ' O centage of acetone is E determined by Mes15 senger's method, a standard acetone being D, used to standardize the iodine solution. A set of standard mixtures is e made up containing 0 the same percentage of 20 30 40 50 60 70 acetone as found in the % o f Propyl Alcohol sample and varying FIG,4-MIXTWRES OF PROPYL AND BUTYL proportions of ethyl ALCOHOLSTITRATED WITH WATER AT 200 C. a n d butyl alcohols. Curve A-Normal propyl alcohol; Curve Turbidity titrations are B-lsopropyl a'coho1 then run on all the standard mixtures and the sample, and the percentage ethyl alcohol in the sample is thus determined. To eliminate the work involved in making new standards for every analysis, a set of curves is being prepared for mix-
*
4
I N D UXTRIAL A N D ENGl ‘NEERINGCHEMISTRY
April, 1924
tures containing 24, 26, 28, up to 36 per cent of acetone, each one with a varying ethyl and butyl alcohol content. The general appearance of these curves is shown in Fig. 3, The percentage of acetone as found by Messenger’s method and the volume of water necessary t o produce cloudiness determine the position of a point corresponding to a certain percentage of ethyl alcohol, which is read off from the horizontal c o o r d i n a t e of that point. This range of 22 to 36 per cent of acetone is sufficient for % Ethyl Alcohol FIG.5--cURvES A , B , A N D c. MIXTURESmost needs, I n case OF ETHYL ALCOHOLAND BENZENE. 100-CC. of samples containing SAMPLE Curve A-Titrated with 50 per cent ethyl more Or less acetone, alcohol; Curve B-Titrated with water a t either acetone or butyl 30° C.; Curve C-Titrated with water a t 20’ alcohol can be added to e.;Curve D-Mixtures of ethyl alcohol a n d bring it &hin that chloroform titrated with water. 50-cc. samDle range. OTHERAPPLICATIONS OF METHOD Of
These turbidity methods are applicable to a large variety of analyses, several examples of which are given herewith. MIXTURE OF PROPYL AND BUTYLAxoHoLs-curves for mixtures of propyl and butyl alcohols, as well as for those of isopropyl and butyl alcohols, are shown in Fig. 4. It will be noticed that the increase caused by either of the propyl alcohols in the solubility of water in butyl alcohol is much smaller than tlie similar effect of ethyl alcohol. This shows an interesting extension of the well-known law of the decrease of the mutual solubility of water and organic liquids with the ascent in the homologous series. This law, unlike the similar laws of the rise in boiling and melting points, is usually limited to the few members of the series that have limited but measurable solubility relations to water. In the case of the saturated :diphatic alcohols, it is limited to the Cq to C, members, since the lower ones are miscible in all proportions with water, while tlie higher ones are practically all equalry insoluble in water . If , however, 50 whttt might be termed “solution affinity” is 4 $ 25 substituted for plain 9 solubility relations, the 4 20 series is extended and ? the applicability of the is law to water-miscible alcohols can also be e 10 demonstrated, s i n c e , while they all possess 5 sufficient “solution affinity” for water to be / L 65 J5 Jo J5 miscible in all propor% of m y / Aicohoi tions with it, considerFIG.&-MIXTURES OF ETHYL ALCOHOLAND able differences bePETROLEUM PRODUCTS TITRATED WITH WATER tween them are found Curve A-Ethyl alcohol and petroleum when they are called ether; Curve B-Ethyl alcohol and gasoline; upon to yield some. . of. Curve C--Ethvl alcohol and kerosene this power to a third substance, such as butyl alcohol. Similarly, while all the higher members of the series appear equally insoluble in water, the effect of ethyl alcohol on making them partly soluble in water will be found greatest for the substance having the lowest position in the homologous series. Such an ex-
5 ;
jo
383
ample is shown later in the case of petroleum ether, gasoline, and kerosene. By deriving the equations corresponding to the curves in Figs. 1 and 4 it might be even possible to obtain certain mathematical relations for the “solution affinities” of the different water-miscible alcohols. MIXTURES OF Two SOLUBLE LIQuIns-Mixtures of two substances, both of which are miscible with water in all proportions, such as those of ethyl and propyl alcohols, can be analyzed by mixing a measured volume of such a mixture with a known volume of an insoluble liquid such as butyl alcohol and titrating with water. It is seen from Figs. 1 and 2 that an ethylbutyl mixture containing 45 per cent of ethyl alcohol requires 36.4 cc. of water per 20 cc. sample, while a similar pro- I pyl-butyl mixture would become turbid j b with 8.5 cc. A water titration curve for mixtures of the three alcoll hols could be made up 2 4 0 in which the butyl alco- e hol nronortion would be Eonstant (45 per cent) and the difference in water titration values would be indicative of the proportions . 0 IO 20 30 40 50 60 between the two lower % of B u i i / l Alcohol FIG.7 alcohols. A difference Curve A-Mixture of butyl alcohol a n d Of 28 CC. Of Water for a butyl acetate titrated with mixture of 60 per 20-c~.sample \vi11 be cent butyl alcohol, 15 per cent ethyl alcohol, to determine and 25 per cent water. 25-cc, sample
2
’’
Curve B-Mixture
of butyl alcohol a n d
these proportions with- butyl chloride titrated with mixture of 85 per in 1 per cent, but more cent butanol and 15 per cent water. 50-cc. delicate results can be obtained by employing larger samples. Note.-In making up all the curves shown (Figs. 1 to 4), the alcohols used were not anhydrous but some especially prepared by adding 3 t o 5 per cent of water to them and drying with a considerable excess of potassium carbonate. This was done because in ordinary practice it is inadvisable to prepare the anhydrous alcohols by distillation on account of losing a disproportionate part of the lower boiling constituents of the mixture in the process. Therefore, the final drying of all samples was effected with potassium carbonate, and as this leaves them with some water-about 1.8 per cent for butyl alcohol, 3 per cent standard for acetone, and 7 per cent for ethyl alcohol-the mixtures for the curves were made up in the same way.
BENZENE AND ETHYL ALcoHoL-Mixtures of benzene and ethyl alcohols, which have been proposed for use as motor fuel, are readily analyzed by the turbidity method. The favorable range is 50 to 90 per cent of ethyl alcohol, as seen from Fig. 5 . For lower concentrations of ethyl alcohol the method used in the ethyl-butyl analysis-that of adding sufficient ethyl alcohol to bring the mixture within the proper range-can be employed. A new modification of the method for this analysis has also been developed-that of titrating with a solution of 50 per cent ethyl alcohol instead of distilled water. I n this way Curve A , Fig. 5 , is obtained, where the favorable range has been moved down to 30 per cent ethyl alcohol. The end point in either method is very sharp, the emulsion formed being very stable. Larger samples have to be used for determinations (100 cc. instead of the 20 cc. of an ethyl-butyl analysis), as the volume of water necessary would otherwise be too small. PETROLEUM P R O ~ U CAND T S ETHYLALCOHOL-A similar curve for ethyl alcohol-gasoline mixtures is shown in Fig. 6.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
In order to learn whether the quality of the gasoline would be a considerable factor, the values for mixtures of ethyl alcohol with petroleum ether and kerosene have also been determined. It will be seen that the three curves, while similar in direction, are different in value. The turbidity method would therefore be applicable only where the quality of gasoline is fairly constant-for exam~le,as a d a n t control method in a refinery where such mixtures would be prepared. It would not be trustworthy in general analysis. On the other hand, it might find use in testing the quality of the different petroleum products in a way similar to the use of specific gravity at present. The reason for the difference between the three d i f f e r e n t curves in Fig. 6 was mentioned in the discussion of the different water-miscible alF I G . S - S ~ L ~ T I O N S OP ETHYLALCOHOLIN cohols. WATERTITRATED WITH BUTYLALCOHOL ETHYLALCOHOL AND CHLOROFORM-A curve for mixtures of ethyl alcohol and chloroform is shown in Curve D, Fig. 5 . The curve is very similar to the one for ethyl alcohol and benzene. ETHYLALCOHOL AND ETHER-Mixtures of ethyl alcohol and ether were tried. The end point is not so sharp as in the preceding examples, since the emulsion is very unstable and the phases rapidly separate into large drops. It is possible that by adding a stabilizing agent to the water a more stable emulsion, and therefore better end point, will be obtained. As yet such a substance has not been found. Other common binary mixtures to which the water titration method can probably be applied are (1) etbyl alcohol and ethyl acetate, (2) ethyl alcohol and ethyl chloride, (3) ethyl alcohol and any insoluble ester, (4)acetaldehyde and paraldehyde, (5) ethyl alcohol solutions of essential oils, (6) acetic and butyric acids analyzed similarly to mixtures of ethyl and propyl alcohols, and ( 7 ) pyridine and quinoline or other coal-tar products. A great many more applications will undoubtedly suggest themselves to the plant and research chemists who are acquainted with their particular needs. APPLICATION TO DIFFICULTLY SOLUBLE SUBSTANCES-In all the applications of the turbidity method given so far, one of the components of the mixture was miscible with water in all proportions. This, however, is not a necessary condition. While the end point is best where there is a considerable difference in the solvent power for water between the components of the mixture, the method can nevertheless be used even where this difference is small. Mixtures of butyl alcohol and butyl chloride, as well as mixtures of butyl alcohol and butyl acetate, of which even the alcohol only dissolves about 17 per cent of water, can be analyzed by the turbidity method. I n such a case, however, a titration with water itself cannot be employed, since the volumes of water needed are very small at the highest. Therefore, a mixture of 85 per cent butyl alcohol and 15 per cent water is employed as the titrating liquid, thus introducing the water in a more diluted state. By introducing some butyl alcohol with the water, the slope of the curve becomes steeper and very similar to the titration curve for ethyl-butyl mixtures. The end point
Vol. 16, No. 4
is not so sharp as where one of the components of the mixture is miscible with water, being an opalescence rather than a turbidity, since the volume of actual water introduced is not very large. Still, within the favorable range of 30 to 55 per cent of butyl alcohol, results accurate to within 1 per cent can be easily obtained if a 50-cc. sample is used. (Fig. 7) The range could be varied by using other mixtures as the titrating liquid, some containing ethyl alcohol in addition to the butyl. Thus, a mixture of 60 per cent butyl alcohol, 25 per cent of water, and 15 per cent of ethyl alcohol makes a very good solution for analyzing mixtures of butyl alcohol and butyl acetate, as shown by Curve A , Fig. 7. USE OF ORGANIC LIQUIDSAS
THE
TITRATING MEDIUM
Liquids other than water can also be employed fls the titrating medium. This solution of ethyl alcohol in water can be analyzed rapidly and accurately by titrating with butanol. The method is almost as accurate as the specific gravity method in use now, and is far simpler, involving simple volumetric manipulation instead of the complicated technic necessary for accurate specific gravity determinations. This method would also be especially useful as a check on the specific gravity results where the presence of other substances is suspected, similar to the use of refractive index measurements a t the present time. (Fig. 8) This branch of the turbidity titration method can be made very fruitful and can find uses even in such unexpected fields as the analysis of inorganic salts. The strength of solutions of salt could be determined by titrating with acetone or other organic liquids, since the presence of salt in the liquid decreases the mutual solubility of water and the liquid. In case of a single salt it is doubtful whether the turbidity method will have any advantage over the specific gravity method. In case of mixtures of two, however, titration with an organic liquid might often be made to give information as to their proportions. This would be especially true with salts of dissimilar elements, or, still better, with mixtures of watersoluble organic and inorganic substances. This method has been tried on mixtures of ammonium chloride and aniline hydrochloride, using acetone as the titrating liquid. The curves are given in Figs. 9 and 10. It will be seen from the curves that solutions of ammonium chlo-
g013az4z
80
% N&CI in Solution FIG.Q ~ O L U T I O N SOF AXMONIUMCHLORIDE IN WATERTITRATED wrm ACETONE Curve A-Titrated
at 1Q0 C.; Curve E-Titrated
at 28'
C.
April, 1924
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
ride itself could be analyzed by titrating with acetone. Solutions of aniline hydrochloride, on the other hand, are not precipitated by addition of acetone. Mixtures of the two in the dry state could be analyzed by dissolving a definite weight in a definite volume of water and titrating with acetone, as shown in Fig. 10.
385
tone and in butyl alcohol are given in Fig. 11. The range is necessariIy very smalI, but can be extended by mixing the sample with some of the same substance containing a known percentage of water. The end point is fairly good, especially a t the middle of the curve. By the use of other liquids, such as carbon disulfide or xylene, a slightly different range and a possible improvement of the end point could probably be obtained. This method has the advantage over the specific gravity method, not only in being simpler and more rapid, but also in being based on a property-extreme insolubility of water in benzene-that is not shared by most of the impurities found in organic liquids, while the specific gravity might be affected by a greater number of them. This method promises t o find application, not only in determination of water in organic liquids, but in determination of water in a great number of solids as well, by transferring their water to an organic liquid as an intermediary agent. By choosing butyl alcohol, for example, as such an agent, several modifications of this method appear possible.
(a) In case of finely ground solids that are insolubIe in butyl alcohol and have their water on the surface of the particles, such as sand, the solid can be shaken up well with the alcohol and the water determined in an aliquot portion of the filtered alcohol. ( b ) Solids that cannot be made to give up their water easily, as well as solids that are soluble in alcohol and would interfere in the subsequent titration, could be heated together with butyl alcohol under a reflux condenser and part of the alcohol distilled and collected. Butyl alcohol forms a constant boiling mixture with water a t 91" C., and is very effective in removing water. If the distillation is kept up until the temperature reaches 110"C., % N H L I i n Mixlure all the water will be found in the distillate, where it can be FIG.10-20 P E R CENT SOLUTION OR M I X T U R E OF NHtCl AND CeHsNHzHCl determined by a benzene titration. By using a compact disTITRATED WITH ACETONE AT 2 8 O C. tillation apparatus of the nature of a Kjeldahl still, this method can be easily applied to routine work. USE OF TURBIDITY METHODIN IDENTIFICATION OF ORGANIC ( G ) With substances soluble in both butyl alcohol and benzene and whose presence in the alcohol would therefore interfere but SUBSTANCES little with the determination of the water, the substance might Like d l analytical methods that are based on the numerical be dissolved in the alcohol and the resulting solution titrated value of a certain physical property of a substance, such as with benzene. Special tables will be necessary for each substance.
specific gravity, index of refraction, etc., the absence of almost all foreign substances must be assured. This limits the use of the turbidity methods of analysis where the qualitative composition of the mixtures is known, either from a knowledge of its source or its method of purification. These conditions are met mainly in plant control analyses and in certain research preparations. The commercial analyst cannot use any such single method with full assurance, since, taking the case of the specific gravity method as an example, the number of combinations possessing the same specific gravity is very large. To him the use of two independent physical methods, based on entirely different properties of the substance, can serve as a useful check on each other and on the real nature and purity of the sample. I n a similar manner the turbidity titration values could be advantageously employed as constants for the identification of pure organic compounds. By determining several such constants, using substances of widely different types as the known components of the binary mixtures, the identification of the unknown can probably be made very dependable. I n this way the sohbilitg relations of organic compounds can be employed in a quantitative way and in very great number of possible combinations, using the simple technic of volumetric analysis. The method can also find application in specifications for defining the desired purity of technical products.
\\
90.
DETERMINATION OF WATERBY TITRATION WITH BENZENE The use of benzene and similar liquids as a qualitative test for water in organic liquids is well known. It can also be used for quantitative determination of this water by measuring the volume of benzene necessary t o produce the turbidity. Curves for such determinations of water in ace-
0
2
3
4
5
6
7
8
9
% HpO FIG.11-SOLUTIONSOF WATERIN ACETONEAND BUTYLALCOHOL TITRATED WITH BENZENE Curve A-Butyl alcohol solution at 20° C. 10-cc. sample; Curve 8Butyl alcohol solution at 30° C. IO-cc. sample; Curve C-Acetone solution a t 20' C. 60-cc. sample
INDUSTRIAL AND ENGINEERING CHEMISTRY
386
These methods of determining water are of special advantage where drying hy heat int.roduces certain errors. Such are slightly volatile solids, as benzoic acid or ammonium chloride, and substances which are oxidised or in any way changed by the heat, as soft coal and some vegetahle produats. In the case of materials where powdering and grinding in the air is objectionable on account of the rapid change in tlicir water contents, the grinding can be done under the surface of the liquid.
Vol. IF, s o . 4
The method could also he used fis manure in t,he compost heap). Fig. 2 is a close-up of the cut.ting edge and propulsion mechanism. A seamless steel tube, A , 12 inches long, l'/s inches outside diameter, 1 I H . W. G. (0.120-inch) wall, lias cut 011 the out-side a right-hand thread of '/rinch pitch the entirc length of the tuhe. A circular knife, R,of tool steel, turned with an inside diameter of 1.405 inches, is attached by drivc fit to FYO. 1 the inside of the tube at one end. The inside diameter mentioned is maintained for inch from t.he outer end, whence the diameter is increased on a short taper to flush with the inside diamet.er of the tube-that is, 1.615 inches. The outer diameter, including a short portion of the tuhr, is turned to give a knife edge tapering hack at an angle of 30 degrces. A nut., C , 5 / 8 inch thick, fits the thread 011 the tube and is carried in the yoke, D , by two pivot bolts, one of which is shown at E. A hole is drilled through and at right angles to the long axis of the tube, 1inch from the end opposite
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Received February 11. 1924.
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the knife. 4 rod may he put through this hole to operate tlie sampler by hand power, or an electric motor may he used for power, as in the illustration. The motor pictured is a high-speed drill motor with special gearing and spindle. The spindlc fits loosely inside the tube and is providpd widh a 'irinch hole, wliich is used in attaching it to the tube hy a bolt or pin, F. The sampling tube, with yoke, weighs 10 pounds. The motor weighs 29 pounds, is rated at horsepower, and op crates from any 110-volt circuit by coirnection t,hrougli the cord, 1. The operating switch is shown at. G, and a reversing switch at H . The motor has a no-load soeed of ROO0 r. p. in. and a full load speed of 3000 r. 1). m. Ilehuoing gearing &es a s"indle s ~ e e drat.io of i:iso. . In use for sampling silage, for examplc, t,hc operat,or holds the sampler in a vert.ical posit,ion as pictured, with the yoke, D, rest,ing on the surface of tlie silage in tlie silo a t the point at which it is desired to take tlre sample. He stands on t.he har of the yoke, one foot PM. 2 on each side of the tube, and holds the motor hy the pipe handles. The motor is then start,ed through tlie switch, G, the reversing switch, N, being set to give a right-hand rotation to the driving spindle. The tube is thus forced int,o tlie silagr at a uiriforni rate, the eireular rotnting knife cutting a core xdiich is forced int.0, and retained within, the tube. When the depth of sanipling desired has been reached (usually the depth of silage that will probably be used during the ensuing feeding period or subperiod), the motor is stopped, the reversing switcti thrown, the motor again operated until the tube is withdrawn, and then stopped. The motor is then detached and the core of silage removed from the tube. The sampling of loose hay in tlie mow is quit.c similar to that for silage. In sampling haled hay or straw, the hale is laid on the floor and the yoke attached to the bale at one end by a rope passing around the bale lengthwise. The tube, with motor attached and resting on the floor, is entered in the imt, the motor started, and a core is cut the entire length of tlie bale, while the operator has merely to sit on the bale
