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A-YdLI'TICAL EDI TIO-Y
side tubes with stopcocks lead froin this tube to the reaction flasks. Reference is frequently made in the literature to the fact that it is desirable to add the nitric acid slowly. With these tubes the acid may be allowed to drip as s l o ~ d y as desired. Actually, the acid is most efficient v-lien it is added just at the cliarring point of the organic material. T h e most effective of several lubricants tried on the stopcocks was graphite. The reservoir containing nitric acid (C) is placed so that the acid runs by gravity to the stopcocks after the siphoning action has been established. The E reservoir may be an ordinary acid b o t t l e on a ring-stand s u p port. A pos=.ible modification would be a pear-shaped reservoir, suspended from a net, with a glass delivery tube sealed t o t h e & "3 bottom. This m u l d E obviate the annoyance of occasionally having Figure 3-Detail of Figure 2 t o s t a r t t h e siphon again, but would introduce an additional danger of breakage. The acid is delivered to this reservoir by pressure
1-01. 2 ,
KO.
1
from a much larger storage reservoir not shown in the diagram. Kjeldahl flasks ( D ) of 800 cc. capacity, reduced to a convenient length (in t'his case 28 cm.), are used. The lips should not be re-formed, as this causes them to catch on the edge of the holes in the outlet cylinder. By making a slight depression (D,Figure 3) it is possible to insert the mouth of the flask further into the cylinder, thus increasing the efficiency of fume disposal. The gas is delivered froin the intake (E) to horizontal Bunsen burners, bent as indicated. This effects a great saving in the height of the apparatus. The valves of the burners are also out far enough to allow convenient access. Iron support rods ( F , Figure 3) for the glass tube ( B ) , not shown in Figure 2, are used. An asbestos curtain (G, Figure 3) reduces the amount of heat reflected from the upper row of burners against the stopcocks on the acid delivery tube, not shown in Figure 2. This arrangement permits the use of a double tier of apparatus. The lower tier may be devoted t o the actual oxidation, and the upper tier to the final expulsion of nitrogen oxides and the destruction of the nitrosyl-sulfuric acid. The long-neck glass wash bottle described is very convenient for adding water to the flasks in position. The stream should be directed against the wall of the flask rather than directly into the acid. The addition of a small amount of ammonia will aid in completing this reaction. This apparat'us is distinctly more efficient in the disposal of fumes, consumption of reagents, and saying of time than the simple equipment first described. Literature Cited (1) Barnes, IXD.ENG. CXEX., 21, 172 (1929). (2) Barnes and ?rIurray,Ibid.,21, 1140 (19291. (3) Barnes and Murray, I b i d . , Anal. Ed., 2, 29 (1930).
A Convenient Arrangement for a Titration Table' J. W. Stillman and T. L. Bartleson E. I.
DU
Pow
DE
SEXOCRS & C O U P ~ VnYr~~ ~ ~ i v c r DEL ou.
HEN standardized solutions for volumetric analysis are used regularly in considerable amount, it is advisable to make up large quantities a t a time. For convenience the bottle containing the standard solution should be connected to the buret in some form of a closed system. One common method is to place the stock bottle on a shelf above the laboratory table, the buret being filled by gravity flow. This arrangement has several disadvantages, chief of which are that if a leak develops in any part of the line connecting the bottle and the buret the whole solution may run out, and that when several solutions are maintained the row of bottles and connecting tubes makes a clumsy appearance. The accompanying figure shows a convenient arrangement which presents a neat appearance. A is a 20- or 40-liter bottle which is set on the floor below the table. In one hole of the stopper is inserted a soda-lime tube through which air enters as the solution is used. Through a second hole runs a glass tube reaching to the bottom of the bottle and connecting with the three-way stopcock of the buret. The buret is mounted on a special rod, B. This rod is hollow and has two clamps (A. H. Thomas Co., catalog number 3236) welded on in the positions shown in the figure. The rod is 1 Received September 30, 1929. Contribution 21 from the Experimental Station of E I . du Pout de Nemours & Company.
t h r e a d e d for several' inches a t the lower end and by means of two nuts is clamped to the wooden table top, C. The working suiface of the table. D. is of white T'itrolite, and it is not desirable to put any pressure on this material. A t the p o i n t where the rod passes through the table a thin, loose collar, similar to those used in plum bi n g pr a ct i ce where faucets are attached to porcelain, is used. Both ends of the rod are finished for rubber-tube connections. A t the top an i n v e r t e d U - sh a p e d glass tube makes the connection between the
1) -4 I
E
January 15, 1930
ISDL-STRIAL d S D ESGIL%ERISG CHEMISTRY
top of the rod and the top of the buret. At the bottom the rod is connected by means of rubber tubing to a tee. From one branch of the tee tubing runs to a valve on the vacuum line, E. The handle for operating the valve is placed on the front of the table. The other branch of the tee is connected through the trap bottles, F and G, to the open glass tube, H, which just projects through a rubber stopper set in the top of the table. The trap bottles are filled with soda lime t o filter the air which enters at H. T o fill the buret, the vacuum is turned on and the stopcock
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of the buret is set to connect with the stock bottle. By placing a finger on the open end of the tube, H, the flow of the solution into the buret can be controlled. S n y number of these units can be combined to provide for the standard solutions which are in regular use. The only parts of the apparatus visible above the table are the burets, supporting rods, and short lengths of glass tubing attached to the bottoms of the burets. A nickel-plated finish for the rods and clamps is satisfactory in the laboratory. T h e burets can be removed easily for cleaning or calibrating.
Physical Methods of Separating Constant-Boiling Mixtures' Arthur A. Sunier and Charles Rosenblum U K I V E R S I T Y OF
ROCHESTER, ROCHESTER, h-. Y .
The physical methods of separating constant-boiling separating constant-boiling mixtures are reviewed. Examples of industrial applimany solutions of liquids mixtures has been of great cations are given wherever possible, although emphasis cannot be separated into commercial importance. The is placed upon general principles involved in the propure components merely b y superiority of absolute alcocedures. Engineering detail is omitted, the theoretical distillation. I n a binary syshol over the azeotrope conbasis being stressed. Certain possibilities are sugtem, for example, only one taining 4.43 per cent water as gested which have as yet had no trial. of the constituents can be a solvent for certain nitrocelThe methods are divided into two classes, according obtained in a pure condition. luloses has interested industo the existence of mass or vapor pressure differences I n addition there is formed a trial chemists. The use of between components. Among the first group are iiiixture of constant boiling absolute alcohol mixed with atmolysis, non-equilibrium evaporation, thermal difpoint and of definite composihydrocarbons as a low-temfusion, and centrifuging. The second division depends tion depending only on the p e r a t u r e m o t o r fuel h a s upon reduction of pressure, formation of three-compressure. T h i s property further directed attention to ponent systems by addition of a liquid or solid, or the b y v i r t u e of w h i c h c e r the problem and has resulted production of solid phases. The use of silica gels is t a i n liquid mixtures distil in numerous patents involvmentioned. a t a constant temperature ing both physical and chemiunder a constant Dressure cal methods of setmation. without change in composition is called "azeotropisni." The use of some chemical reaction to remove a n undesiraThere are t n o classes of constant-boiling mixtures, de- ble component from a liquid system has been a common pending on whether the mixture boils above or below the practice for centuries. For example, quicklime was known boiling point of either pure constituent. Their properties as a dehydrant of ethyl alcohol as early as t'he tenth century can readily be seen with the aid of a composition-boiling (26). Howel-er, it is not the immediate purpose to review point diagram. Consider a t constant pressure mixtures the problem from the chemical standpoint. 'The works of of components -4 and B having boiling points t d and le, Patart, (%), Pique (26, E), hlariller (17, 18), and Cooley (5), respectively. Figure 1 shows the variation with temperature on the prepa1,ation of absolute alcohol, from the constantof the composition of the liquid and vapor phases. It is boiling mixture of greatest industrial import'arice have disevident that during distillation both phases approach a cussed quite fully the chemical methods of separation. I n state of constant composition. Obviously, regardless of this paper only methods based on well-defined physical nhich component is in excess, the difference between the principles are to be considered. Certain lines of attack composition of liquid and vapor in equilibrium decreases which have not yet' been imestigatetl but ~ ~ h i seem c h t'o be until a t c the composition of the liquid phase is identical valid will be suggested. For simplicity only binary systems with that of the vapor. Therefore continued fractionation will be discussed, since the theory of ternary systems is not produces no further change in composition. The mixture yet very well developed. Any process which pernianently of composition c and boiling point t , is the maximum azeo- changes the equilibrium concentration of a.n azeotrope, trope. Figure 2 shows similar curves involving a minimum thereby allowing separation by fractionation, will be conconstant-boiling mixture. sidered a solution to the problem in hand. Approximately two thousand cases of azeotropism are Classification of Methods known. Examples of the first kind of azeotropism are the systems: nitric acid-water, halogen acid-water, formic acidThe physical methods of separating constant-boiling mixwater, and chloroform-ethyl acetate. Typical minimum tures fall into two general classes. Certain of these depend azeotropes are: ethyl alcohol-water, ethyl alcohol-carbon on differences in mass of the components. Abmolysis, nontetrachloride, methanol-chloroform, acetonecarbon disulequilibrium eyaporation, and thermal diffusion are examples fide, and ethyl alcohol-water-benzene. More detailed in- of this division. Centrifuging has also been suggested ( $ 2 ) . formation concerning this phenomenon is given b y Young Other met'hods involving vapor-pressure relations have (41) and Lecat (14, 15). found greater commercial application. Among these are Aside from its purely scientific interest, the problem of variation of pressure and addition of a third component, ' Received M a y 10, 1929 either a liquid t o form other azeotropes or a sohd which will
T I S well known that
