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or more. Considering the usual accuracy of a determination the agreement may be regarded as good.
calculated values in Tables 11, 111, and IV. Most of these mixtures have a vegetable oil as one constituent, and i t is Data from the Literature remarkable that the agreement is as good as it is. I n the Some values for the flash points of mixtures were found single case, Table 11, where two mineral oils are mixed, the recorded in the literature. These are compared with the greatest deviation is 7".
Determination of Paraffin Wax in Crude Wax' By L. M. Henderson and S. W. Ferris THEATLANTIC REFINING Co., PHILADELPHIA, PA.
RESENT methods for the analysis of oil-wax mixtures has certain decided advantages over other methods and one are not altogether satisfactory. Some give results of of the most important of these is a working temperature of doubtful accuracy and others are long and tedious. 15.6" C. (60" F.), instead of the low temperatures employed The several methods are of three types-namely, those by earlier investigators. involving (1) a pressing process, (2) a sweating process, and One inherent fault in all these solvent methods is that (3) a separation of oil and wax by means of selective solvents. they require one or more transfers of the wax or wax soluThe press method2 does not give satisfactory quantitative tions. The acetone method, for example, involves two transresults. The sweating process3 is tedious and of doubtful fers and a filtration. There is difficulty in maintaining a c c u r a c y . Selective- Solconstant temperature while vents have been used by filtering and washing, and if several investigators. the temperature rises some A method for determining wax in oil-wax intermediHolde4 employed a 50:50 wax, goes into the filtrate. ates has been developed which obviates objectionable mixture of absolute alcohol T r a a e r s of wax are obfeatures of previous solvent methods. Nitrobenzene and ether and precipitated j e c t i o n a b l e because the is used as the selective solvent. the wax from solution by physical properties of wax An apparatus has been devised which makes i t poschilling to -20" C. This are such that it is practisible to carry out the entire procedure of separating cally impossible to transfer method necessitates mainand weighing the wax without transferring the sample. taining a constant temperait repeatedly n-ithout loss. The working temperature is never below 32" C. The To avoid this loss it has ture of -20°C. throughout melting point may also be determined in the same the various steps in the probeen the usual practice to apparatus. cedure. It is neither easy weigh the oil and determine nor convenient to maintain t h e wax b y difference. this low temperature conHowever. if there have been stant during t'he successive filtrations and washings required. one or more transfers or filtrations in the procedure, an exMethylethyl ketones has been suggested, but its use also re- cess of solvent has been used for washing purposes and some quires cooling to -20 " C. Wilson and Wilkinse have described of the wax has surely been dissolved. The result is a lorn a solvent-index of refraction method of determining oil in wax value for the wax content of the original sample. It is the purpose of the present investigation to modify which makes use of ethylene dichloride. Here also the filtration and washing are carried out in a Holde apparatus at - 18" the method of Wyant and Marsh so as to eliminate the transC. (0" F.), However, instead of weighing the residual oil ob- fers and filtration and to develop a dependable and rapid tained after evaporating the solvent from the filtrate, it is method of analysis. Acetone was found to be unsatisfactory dissolved in a special mixture of mineral seal and ligature oils when tried out under the conditions here imposed. Thereand the index of refraction of the solution determined a t fore, nitrobenzene was tried, for it is well known that it may 25" C . (77" F.). The amount of oil present in the solution be used for separating oil and wax. is then ascertained from a reference curve which relates index of refraction with the oil content of standard solutions. Solubility of Wax and Oil in Acetone and Nitrobenzene The wax is obtained by difference. The authors state that To establish the suitability of nitrobenzene for the purpose, the method is not so simple as might be desired. Wyant and Marsh' conducted an extended investigation the solubilities of both wax and oil were first determined in each of the two solvents. The oil was pressed heavy paraffin on the analysis of oil-wax mixtures by the solvent method. distillate, and the wax a finished plant product from paraffin Among the solvents studied by them were acetone, a very distillate. The method of determining the solubilities was volatile gasoline, benzene, and ethyl acetate. They conas follows: cluded that acetone was especially suitable for use in the separation of oil and wax. The method which they evolved A weighed amount of the solute was put into solution in the
P
1 Received August 28, 1926. Presented under the title "Determination of Wax in Intermediates" before the Division of Petroleum Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1926. 2 Day, A Handbook of the Petroleum Industry, Vol. I, p. 724, John Wiley 81 Sons, Inc., 1922. 8 Holde-Mueller, "Hydrocarbon Oils and Saponifiable Fats and Waxes," 2nd ed., p. 249 (1922). 4 Holde-Mueller, loa c i t . , p. 108. 6 I b i d . , p. 110. 4 THIS JOURNAL, 16, 9 (1924). Bur. Mines. Tech. Paper 368 (1926)
solvent, by heating in the case of nitrobenzene, and by means of a reflux distillation in the case of acetone. The first solution prepared was of high concentration. The dilute solutions were prepared by mixing a portion of the stock solution with a definite amount of the fresh solvent.
The cloud point of each solution was then determined, first by slowly cooling until the cloud could not be eliminated by shaking, and then by gently heating until the cloud just disappeared. The points so determined were found to check closely.
I S D U S T R I A L AND ENGINEERI?IG CHEXISTRY
February, 1927
The solubilities are shown in Figure 1. It will be noticed that, although the wax is very slightly more soluble in nitrobenzene than in acetone, the oil is very much more soluble in nitrobenzene. The difference in solubility of wax and oil is very much greater in the nitrobenzene; in other words, the nitrobenzene is better adapted to the separation of the two constituents than is acetone. Apparatus
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to about 10" C. is now introduced into the jacket, and the temperature of the mixture reduced to 32" C., bubbling air about five times as rapidly as during th? heating period. The mixture is held a t 32" C. for 5 minutes. This temperature was found to yield a wax, from the majority of samples, of 50" to 51' C. (122" to 1 2 4 ° F . ) melting point. On account of the high specific gravity of the nitrobenzene the wax floats on the surface, with the oil-nitrobenzene solution in the narrow test-tube portion.
The flask (Figure 2) was made by sealing about 1 inch of an ordinary Pyrex test tube to the bottom of a 300-cc. Kjeldahl flask, and cutting off a large part of the neck of the flask. +4glass rod was sealed to the bottom of the test tube. The flask was jacketed by placing it in a tall 1-liter beaker, in the bottom of which was placed a layer of asbestos cement, about 314 inch deep. -4hole was formed in the center of the asbestos layer to fit the glass rod closely a t the bottom of the flask. The beaker was covered by a l/*-inch asbestos board, with the necessary openings. The cork bears a capillary tube drawn out to a point, a thermometer, and a short glass tube. X similar capillary tube, but without a cork, is necessary for the removal of the oil-nitrobenzene solution. Procedure
X 10-gram sample of the material to be examined is weighed into the flask. T o insure a representative sample, the material should be melted, thoroughly stirred, and the sample taken while liquid. A wire loop around the neck of the flask facilitates weighing. The flask is placed in the beaker, and 20 cc. of nitrobenzene are added. The cork is adjusted as in Figure 2 except that the short tube is not connected to suction. The temperature of the mixture is raised t o 70" C. by the introduction of heated air into the jacket. During this heating period air, controlled by the needle valve, is bubbled slowly (about one bubble per second) through the mixture. As soon as the liquid has reached TO" C. the stream of hot air is stopped. Air cooled
-
TLMPLRAIURL DlGRfLS CCNT/C.QA OC
Figure 1
Air _L
Figure 2
The cork is removed and a capillary t h e introduced in such a manner that it reaches the bottom of the narrow portion of the flask. The oil-nitrobenzene solution is drawn off through the capillary tube by means of suction. A second portion of 20 cc. of nitrobenzene is added, and the foregoing procedure repeated. After the second separation the cork is again replaced and the short tube connected with the suction flask, exactly as in the drawing. The wax is heated to 135" C. by introducing hot air into the jacket. After this temperature has been reached suction is applied to the flask. -4large portion of the nitrobenzene remaining in the flask is immediately volatilized, causing a drop in temperature. The vapors are easily condensed in the suction flask, no cooling being necessary. The temperature of the wax is now brought up t o 150" C. and air, controlled by the needle valve, bubbled through it. The agitation a t this point is as vigorous as is possible without risking the loss of the wax. The air is allowed to bubble through for 15 minutes. The Capillary tube is first raised out of the wax, then the suction and heat are shut off and the cork is removed. The melting point of the wax may now be determined, in the flask, by introducing a suitable thermometer and noting the temperature every 30 seconds as the wax cools. The flask may, if desired, be removed from the jacket to determine the melting point. The solid wax on the thermometer is quantitatively returned to the flask, and the yield is de.% termined by weighing. If desired, the yield may be determined before taking the melting point. This requires a slightly longer time, since the flask must be allowed to cool before weighing and then reheated to determine the melting point. The temperatures given above for the removal of nitrobenzene have been found convenient when using a pump capable of about 50 mm. pressure. If such a pump is riot available, a weaker suction may be applied and the temperature of the wax raised somewhat higher. Indeed, the
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suction may be entirely omitted. I n this event, howerer, the air agitation must be accomplished by air pressure instead of air leakage. Fortunately, the odor of nitrobenzene is so strong that it indicates the presence of minute quantities. The absence of the characteristic odor in the wax is evidence that practically all the nitrobenzene has been removed. Results Typical results obtained on slack waxes are given in Table I. Table I SLACK WAX
YIELD
P e r cent 45.3 45.9 46.8
MELTING POINT
F.
O
c.
123.5 122.0 122.8
50.8 50.0 50.4
2
39.7 36.7
123.9 124.0
51.1 51.1
3
56.2 56.5
124.0 123.4
51.1 50.8
~
These yields check satisfactorily with those obtained in the plant sweating ovens. It is difficult to prepare a “known” slack wax. This was attempted, however, by mixing a finished wax with a sweat oil in known proportions. The results on this synthetic slack wax indicated that practically all the wax is recovered by the nitrobenzene method.
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Discussion Acetone did not prove to be so useful a solvent in this type of apparatus as nitrobenzene. The advantages of using nitrobenzene are evident from the following considerations. The wax obtained by means of nitrobenzene is compact and seems to retain very little of the solvent, while the wax separates from acetone in a flocculent state and tends to retain appreciable amounts of acetone. Inasmuch as the specific gravity of nitrobenzene is greater than that of the wax, the latter collects as a cake on the surface of the oil-nitrobenzene solution. I n the apparatus used, this cake forms just above the narrow portion of the flask with the clear oil in the constricted part, whence i t may be removed without loss of wax. Most of the wax clings to the side of the flask and does not fall down when the oil solution is drawn off. I n the case of acetone i t is impossible to separate the oil solution from the wax sharply by merely drawing off the supernatant liquor, because the wax is flocculent, very slow in settling, and does not form a compact layer. Attempts at filtration were not satisfactory. The greater solubility of the oil in nitrobenzene is advantageous in that smaller quantities are required for a given amount of the sample. Nitrobenzene is also preferable because its complete removal from the wax is quite definitely assured when the wax is free from all odor of nitrobenzene. Acknowledgment The authors are indebted to W. H. J. Xanthorpe for his assistance in the laboratory.
Detection and Determination of Nitrogen-Bearing Chemicals Added to Animal or Vegetable Nitrogenous Materials’ By H. C. Moore and Robert White ARMOUR FERTILIZER WORKS, CFIICAGO, ILL.
H E practice of adding such chemical forms of nitrogen as sulfate of ammonia and cyanamide to so-called nitrogenous tankage by unscrupulous manufacturers has reached the point where attention should be called to it. Since these chemicals can be bought as such for from $1.00 to $1.50 per unit less than the organic form in the tankage, the effect of this practice is obvious. The writers have found sulfate of ammonia in numerous lots of nitrogenous tankage, sometimes cyanamide, and sometimes both of these materials. Nitrate of soda or Leunasalpeter might also be present, although it would be of doubtful profit to the manufacturer, on account of the cost of the nitrate form of nitrogen, and because the usual method of determining the nitrogen present in organic materials is not so applied as to include the nitrate form. Urea, which is now comparatively cheap in Europe, might be added to foreign nitrogenous tankage for import to this country, and thus escape duty. It is not difficult to detect the presence of these various chemical forms of nitrogen, but until recently it has been difficult to determine accurately the quantities, especially
T
1 Presented before the Division of Fertilizer Chemistry a t the 72nd Meeting of the American Chemichl Society, Philadelphia, Pa , September 5 to 11, 1926.
when several are present in the same mixture. The methods of analysis given herein are not all new, but their application in the detection of the practice mentioned above may not be so well known. Mechanical Separation of Cyanamide and S u l f a t e of Ammonia The silver nitrate test for cyanamide usually fails to show this material when present in tankagc. But if some of the sample is mixed with an excess of carbon tetrachloride, a mechanical separation (due to gravi3,y) is made, when the heavy particles, including cyanamid(:, sulfate of ammonia, etc., will settle to the bottom of the container, while the tankage will float. If the portion which settles is tested with silver nitrate, cyanamide is easily detected. This mechanical test may conveniently be applied as follows: PIace 30 to 40 grams of the tankage, preferably ground to pass a 10-mesh sieve, in a beaker or casserrle and add about 200 cc. of carbon tetrachloride and stir. Afte allowing to settle a short time, the lighter floating material, aloug with most of the carbon tetrachloride, is transferred to another container and the heavier portion tested for sulfate of ammoria, cyanamide, etc. If the carbon tetrachloride-tankage mixture is mixed with a n approximately equal volume of turpentine, crystals of urea, if present, will appear floating or in partial suslmxion.
