IVALKER AA-D IVHITMAN O X RAPID ALVALYSI.5 OF BABBITT IZIETAL. ignition this carbonizes instantly and serves to retain the decrepitated particles thrown off in the early part of the ignition. The paste is completely burned away some time before the end of the operation. I n certain cases the crucible containing the coke is more or less attacked, and i t is well, therefore, to use a small boat easily made of thin platinum foil, fitting closely into the larger crucible and high enough to contain the sample. A few of the results obtained in this investigation will suffice to show the difference between the two methods of ignition. -4 one-gram sample of coke lost in seven minutes’ ignition, as in the standard method, with crucible cover, 2.96 per cent. volatile matter. The same sample, when given another seven minutes’ ignition in the same way, lost 1 . 9 7 per cent. additional. Using the same Bunsen flame, a one-gram sample of the same coke, ignited for seven minutes in the double crucible, lost 1 . 2 0 per cent. and, on giving i t an additional seven minutes, the loss was only 0 . 1 2 per cent. To show that all the volatile matter is not driven off by the Bunsen flame alone, the following results, among many similar ones, are given. A one-gram sample of another coke yielded 1 . 5 1 per cent. volatile matter by seven minutes’ ignition over the Bunsen flame in the double crucible. The sample was again heated for three and one-half minutes over the blast lamp and sustained a further loss of 0 . 7 3 per cent. volatile matter. On igniting again for three and one-half minutes over the blast lamp there was no further loss. I t is not necessary to insist on the importance of a fairly accurate determination of volatile matter, for it is not only of value in itself but is essential to the correct determination of fixed carbon.
[COXTRIBUTION FROM THE CONTRACTS LABORATORY, BUREAUO F CHEMISTRY. PUBLISHED BY PERMISSION OF THE SECRETARY O F AGRICULTURE.]
RAPID ANALYSIS OF BABBITT METAL. By PERCY H . WALKER AND H. A. WHITMAN. Received May 21. 1909.
Methods for the analysis of alloys of lead, tin, antimony and copper, which are based upon the separation of lead and copper from antimony and tin by the use of alkaline sulphide solutions, are all exceedingly tedious, though with the necessary care, skill and patience, i t must be admitted that a method based upon this principle gives results
519
of greater accuracy than any of the more rapid methods. This method is, however, so tedious that it can seldom be used in a commercial laboratory, and when i t is used the chances of loss are so great that frequently the whole analysis must be recomnienced after spending several days on the tedious separation. The more rapid methods which are often based upon the separation of antimony and tin by treatment of the alloy with nitric acid are open to the serious objection that one portion of the alloy is used for several determinations and the errors in separation appear again in the determination of the individual metals. It is highly desirable that we have a method using a separate portion of the alloy for each determination, and that the metal to be determined in each case be dissolved before it is determined. Except for the method of separating copper (and even here Fresenius’ gives a similar method of separating copper from nickel), there is no new method suggested in the scheme we present. The details of the various determinations have, however, been studied and sources of error in the determination of lead and copper are pointed out, so that by following the method as described and applying the proper correction as accurate results can be obtained as by the alkaline sulphide process in a far shorter time and with much less labor. THE METHOD. Cofi+er.--Weigh I gram of the alloy into a 2 5 0 cc. beaker, add 2 0 cc. hydrochloric acid and 5 cc. water, heat and complete solution by adding nitric acid in small amounts; with most alloys solution can be effected in a very few minutes and without adding more than I or 2 cc. of nitric acid. Evaporate off the acid on a steam bath. It is not necessary to carry to complete dryness, but practically all the acid should be driven off and the residue should be pasty. Add 2 5 cc. of a solution made of 2 0 0 grams tartaric acid, 260 grams of potassium hydroxide, the whole being made up to 500 cc. with water. Heat on the steam bath until solution is completed, add 2 5 cc. water, boil, add 2 5 cc. of a 0 . 2 per cent. invert sugar solution, boil for two minutes, filter through asbestos, wash the precipitate of Cu,O with water, dissolve in nitric acid, catching the copper solution in a zoo cc. flask, and determine copper by any good volumetric method. We have found that equally good results can be obtained by following Low’s iodide “Quantitative Analysis,”
Vol. 1, p. 684.
T H E JOC'R,VAL OF I S D U S T R I A L A S D E,VGI,VEERI,VG C H E M I S T R Y .
520
method,l or by Jamieson, 1,evy and Wells' thiocyanate and iodate method." The results are uniformly a little low. This error is not due to volumetric methods employed, both of which give exceedingly accurate results; but nearly 6 per cent. of the copper present is not precipitated as Cu,O. This loss is uniform for if we add 6 per cent. of the copper determined, the result will be the per cent. of copper in the alloy. The statement is frequently made that if a Babbitt metal is decomposed by nitric acid, evaporated to dryness, taken up with nitric acid and filtered, that copper can be determined in the filtrate with an error of not more than one or twotenths of I per cent. This is not the case, the error with an alloy containing j per cent. of copper will frequently be from 0.5-0.7 per cent. while by the method described above without correction the error will be less than 0.3 per cent., and by applying the correction this error is removed entirely. Lead.--.Dissolve 0.5-1 gram alloy in a 250 cc. beaker as in the determination of copper, when solution is complete, evaporate to dryness on the steam bath, add j cc. strong hydrochloric acid (with as much as IO per cent. Sb use I O cc. HCl), warm for a few minutes, remove from steam table, add, with stirring, 150 cc. 95 per cent. alcohol, let stand a t room temperature for 2 hours, filter on a Gooch crucible, wash with 95 per cent. alcohol, using about IOO cc. Suck as dry as possible, dry crucible in an air bath (one hour a t I o j O C . is sufficient, though the lead chloride can be heated a t 150' with perfect safety). Weigh as PbCl,, add 0.0085 gram to the weight of the precipitate and multiply by 0,74473, the product gives the weight of lead. The method of separating lead as chloride has been used by several authorities: G. W.Thompseparates as chloride and then determines as chromate. O l ~ e n separates ,~ and weighs as chloride. Neither of these authors, however, give methods which can give correct results, for the soluhility of lead chloride in mixtures of alcohol and hydrochloric acid seems to have been overlooked by both.5 This may cause errors of several A m . C h m . SOC.,24, 1082 (1902). Ibid., 3 0 , 760 (1908). 3 Stillman, " Engineering Chemistry." 3rd E d . , p . 401. 4 " Quantitative Analysis." p . 136. 5 I n Thompson's original article, which was published in /. SOC. Chew. I d , 15, 179-182 (1896). he states t h a t b y using as he does potassium chloride along with hydrochloric acid the amount of lead left in after precipitating as chloride with alcohol amounted t o 0.3 per I/.
2
Aug., 1909
per cent. if the conditions are not made uniform and allowance made for the lead chloride dissolved. The amount of acid present is also of importance. If a large amount of hydrochloric acid is present the liquid will dissolve more lead chloride; if too little acid is present there is danger of precipitating oxychlorides of antimony or tin. We have found, however, that the above proportions of acid and alcohol will cause no precipitation of metals other than lead and will dissolve an amount of lead equal to the correction applied. This holds true for alloys high in lead and for alloys high in tin. ,4ntirnony is best determined by W. H . Low's method' which we have slightly modified as follows: To I gram alloy in a 4 j o cc. Erlenmeyer flask, add 10-1j cc. strong sulphuric acid, and heat on hot plate until alloy is thoroughly decomposed. This is generally accomplished in about 30 minutes from the time fumes of SO, begin to be given off. Cool, add zoo cc. water and 2 0 cc. strong hydrochloric acid, boil to make sure that all SO, is driven off, cool and titrate rapidly with potassium permanganate which has been standardized against metallic antimony. The true end-point is when a pink color shows after agitating the liquid, though this pink will very soon disappear. The only change we make in the Low method of procedure is to add somewhat less hydrochloric acid. The results are sufficiently accurate for commercial purposes, but the tendency is to get results 0.30.4 per cent. high. Tiii is also worked by W. H. Low's method, except that we have found it more satisfactory to use a separate portion of the alloy and reduce with steel turnings instead of with metallic antimony. Treat from 0.2-1 gram of alloy (do not use an amount of alloy containing more than 0 . 2 gram tin) in a 4jo cc. Erlenmeyer flask with IO1 5 cc. strong sulphuric acid, heat on the hot plate until the alloy is thoroughly decomposed, cool, add 2 0 0 cc. water, 30 cc. strong hydrochloric acid, and about I gram of steel turnings, heat and when reduction appears complete, but before the last particles of steel have dissolved, place a two-hole rubber stopper in the neck of the Erlenmeyer flask-one hole of the stopper should carry a tube reaching below the surface of the liquid, the other hole should carry the short arm of a bent tube, cent. when he was working with solder, and i n a private communication since this was written, Dr. Thompson tells us t h a t he makes an allowance for t h e lead chloride dissolved. He, however. weighs his lead as chromate. 1 J , A m C h e m S o c . , 29, 66.
WALKER A,YD WHITAVAzV0.V R A P I D AiVAL Y S I S OF BABBITT ;\iTETAL. the long arm of which reaches nearly to the bottom of a 100 cc. Erlenmeyer flask containing a solution of sodium bicarbonate. This small Erlenmeyer is held on the bent tube by a cork which has a notch cut in i t to act as a vent. Through the tube reaching below the surface of the liquid in the large Erlenmeyer pass a current of carbon dioxide, heat to boiling until all steel is dissolved, continue passing CO, and cool as quickly as possible; loosen stopper hut let current of CO, continue, add cautiously some starch solution and titrate with AT/I O iodine. I t is necessary to absolutely exclude air and to standardize the iodine solution with pure tin. Results are accurate. To test the copper method, amounts of copper, tin, antimony, and lead were weighed out in the proportions of about 4 copper, 13 lead, 8 antimony, and 75 tin, the copper being weighed accurately each time and the copper determined in the mixture as described. The followiiig results were obtained. Weight of mixed metal. Grams.
Copper taken. Gram.
Copper by titration. Gram.
1 1
0.0446 0.0446 0.0446 0.0863 0.0849 0.0407 0.0407
0.0417 0.0422 0.0418 0.0799 0.0803 0,0376 0.0382
1 2 2 1 1
Copper calculated b y taking 106 per cent. of copper by titration. Gram. 0,0442 0.0447 0.0443 0.0847 0.0851 0.0399 0.0405
An alloy, No. 4873, containing 4.66 per cent copper was then taken and the foliowing results obtained : Weight of alloy taken. Grams. 2 2 2 2 2 1
1 1 2 2
Per cent. copper b y titration. 4.35 4.34 4.49 4.42 4.43 4.40 4.37 4.35 4.43 4.39
Per cent. copper h r taking 106 per cent. of copper by titration. 4.61 4.60 4.T5 4.68 4.69 4.66 4.63 4.61 4.70 4.65
Alverage by proposed method, 4.66. Alloy No. 4873 had been previausly analyzed by the alkaline sulphide method with the following results on copper: 4,60, 4.98, 4.37 and 4.68, giving an average of 4.66, the same as by the propose,d method. Xot only are the determinations carried out by our method much more rapidly than by the alkaline sulphide method, but the individual determinaJ tions agree better among themfselves.
52
=
To test the lead method a similar method was followed, the metals being taken in about the same proportion as for testing the copper determination. Varying amounts of strong hydrochloric acid were used and the following results obtained: (0)
ib)
Weight of mixed metals. Grams. 2 2 1 1
(C)
HydroWeight chloric acid of lead. used. Gram. cc. 0.2865 10 0.2819 10 0.1418 5 0.1416 15 0,1472 25 0 1489 10
1
1
(4 \Veight PbC12 found. Gram. 0,3649 0.3603 0,1978 n.1818 0.1777
0.1917
(e)
ti)
Weight of PbC12 0.0085 g. Gram.
Per cent. Pb from
+
(e).
13.60 13.73 15.36 14.17 13.87 14.91
0.3734 0.3688 0.2063 0.1903 0.1862 0.2002
These results indicate that better results are obtained when using I gram of alloy than when using 2 grams and also indicate that as much a s I j cc. of strong hydrochloric acid could be used without changing the results materially. The method was then used in determining lead in two alloys with the following results: (a) (b) Weisht H r d r o of chloric alloy acid taken. used. Alloy. Gram. cc. 4874 1 5 3 4874 1 4874 1 10 10 4874 1 4874 1 15 15 4874 1
(dl (e) (C) Weight IVei gh t of of PbC12 Per cent. PbClz found. .t 0.0085 g. lead Grams from ( d ) . Gram. 0.9924 1.0009 74.57 0.9940 1.0025 74.69 0.9833 0.9918 73.81 0.9942 74.07 0.9857 0.9815 0.9900 73.73 0.9800 0.9885 73.63 [PbCl? stood 0.1683 18 hrs. be0.1768 13.17 0.1761 13.12 fore filter0.1676 [ ing.
'
4873 4873
1
5
1
5
4873 4873
1 1
5
5
0.1661 '0.1636
4873 4873 4873
1
3 2 1
0.1706 0.1689 0.1705
1
1
{
0.1791 0,1774 0.1790
13.34 13.22 13 . 3 3
i
PbCI, stood 2 minutesbefore filtering.
The two alloys used had been carefully analyzed by the alkaline sulphide method with a final weighing of lead as sulphate. No. 4874 gave 74.13 per cent., 74.71 per cent. and 74.44 per cent. lead, averaging j4.43 per cent. lead. KO.4873 gave 13.34 per cent., 13.28 per cent., 13.07 per cent. and 13.33 per cent. lead, averaging 13.26 per cent. lead. On alloy 4874 the results obtained by the chloride method, using I j cc. hydrochloric acid, aie somewhat low, and as I O cc. are enough it is best to use this amount. The last three determinations on alloy 4873 indicate that accurate results can be obtained by using even less than 5 cc. acid and filtering a t once.
522
T H E JOURiVAL OF INDUSTRIAL A N D EHGIAVEERING CHEMISTRY.
The methods for tin and antimony are in all essential respects well-known methods, but we have found in the laboratory that they yield good results as the following indicate: Antimony by alkaTin by alkaline line sulphide Anti- sulphide method method, with final mowwith final weigh- Tin-voluweighing as Sb& volumetric. iug as SnOs. metric. Alloy 17.28 17.76 7.82 7.98 4874 17.33 ,7,46 17.90 8.10 7.92
.... ....
..... .....
17.5,)
17.68
Antimony by alkaline sulpbide method, with final Alloy. weighing as SbzSa. 8.02 1 7.91 I 4873 7.91 8.03
....
.... .... .... .... ....
I
.... .... I .... J
8’28
....
....
.... ....
AntiTin by alkaline monyrulphide method voluwith final Tin--volumetric. weighing as SnOp metric. 8.45 73.98 73.87 8.38 74.03 75.47 1 .... ..... 74.33 1 .... ..... 74.42 } 74.16 73.31 I 74.98 I .... 73.51 J
....
....
..... ..... .....
We wish to express our thanks to Mr. F. W. Smither who made the analyses of the two samples of Babbitt metal by the alkaline sulphide method. He used the method described in N. W. Lord’s ‘ I Notes on Metallurgical Analysis, ’’ 2nd Ed. Also to Dr. H. C. McNeil for suggestions on the various methods tried. [CONTRIBUTION N O .
6
CHEMISTRY OF THE
Aug., 1909
ment of its most important phase, as well as the inaccessibility of Hausbrand’s’ and other pertinent articles,2 especially to American readers, justify the publication of the methods herein developed. In the separation by distillation of a binary mixture of miscible liquids, we have, in the terminology of the phase rule, a divariant system. Throughout this discussion we shall make the assumption that the pressure remains constant, inasmuch as most distillations are carried on under atmospheric pressure, and very closely approximate this condition. All our formulae will hold equally well whatever this constant pressure may be, whether below or above atmospheric, and it must also be mentioned that these formulae apply likewise to distillation a t constant temperature, the pressure being varied as may be necessary to maintain the equilibrium between the gaseous and liquid phases. If, now, this one external condition (pressure or temperature) imposed upon the system, be kept constant throughout, the effect is the same as reducing i t to a mono-variant one. The phase rule, then, tells us that, whichever of the remaining variables we may choose as the independent one, all others are functions
FROM THE RESEARCH LABORATORY OF APPLIED MASSACHUSRTTS INSTITUTE OF TECHNOLOGY.]
THE THEORY OF FRACTIONAL DISTILLATION. BY WARREN R . LEWlS. Received May 4, 1909.
The theory of the separation of a binary liquid mixture into its components coming up for discussion in a seminar conducted by the author in the Research Laboratory of Applied Chemistry of the Massachusetts Institute of Technology, i t was discovered that but very little work has been done on the subject, and that the results already obtained are incomplete and difficult of access. While qualitatively the phenomena are well understood, methods of calculation of the quantitative efficiency of separation by simple distillation have never been developed, and although separation by rectification has been ably treated mathematically by Hausbrand,’ still the developments in physical chemistry since the time of his publication enable us to grasp the concepts involved more clearly than was then possible, and thus to develop the formulae more simply, and to carry them somewhat further than he. The general importance of the subject, the entire absence of quantitative treat1 Hausbrand, “Rectificir- und Distilir-Apparate,” Julius Springer, Berlin, 1893.
of i t alone. Since our problem is the separation of a binary mixture into its components, we naturally choose the compositions of the liquid and the gas above it as our variables. A t constant pressure (or tcmperature) the composition of the gas in equilibrium with a given liquid mix-
’ Zeatschrijt jur S#zral‘usznd, 1884. 1885
1896
