SEPTEMBER, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE11. WAX-COATED TINPLATE CANS Can Size
Quart
0.5gal.
Quart
O5gal.
Grams Can of Wax No, Coating5
-Test of Iron in Varnish,b Months 1 2 3 4 5 6 7 8 9 1 Containing 5 Pounds of Regular Bleached Shellac Varnish 43 6,8 44 6 . 1 0 0 0 0 0 0 0 0 x 45 7 . 7 0 0 0 0 0 0 0 0 0 46 N . C . 0 0 O + + + + + + + t 47 4.8 0 0 0 0 0 0 0 0 x 48 5 0 0 0 0 0 0 0 0 O x 49 6 . 1 0 0 0 0 0 0 0 0 0 5 0 N . C . O O O O + f + + f + Containing 5 Pounds of French Varnish 0 0 0 0 0 0 0 0 0 51 4.8 52 5 . 0 0 0 0 0 0 0 0 0 0 53 6.1 0 0 0 0 0 0 0 0 5 4 N . C . O O O O + x $ + + $ 55 4.3 0 0 0 0 0 0 0 0 0
,
5 .6 7 0 0 0 0 0 N.C. 0 0 0 0 0 N.C. = not coated with wax. 0 = negative test for iron: x = trace of iron present; 56 57 58
b
0 0
0 0
0 0
0 1 1 x 0
0 0
0 0 0 +
x 0
0 0
0
0
+ 0
0
0
0
0
0
0
+ = positive test for iron.
Cans were also coated by being sprayed with either the molten wax or a solution of it in a suitable hydrocarbon solvent. These methods gave some trouble because of the difficulty of obtaining uniform, smooth, adherent coatings, but this was c ~ ~ r e c t eby d Passing the coated cans through a dryer maintained slightly above 70" c.7 the melting ternPerature of the wax. Cans coated in this mmner Protected
0
-
t
the shellac varnish equally as well as those coated by the flushing method. It was not considered practical or advisable to coat the flat terne-plate sheet with wax before fabrication into cans, since the coating would be too easily damaged during the manufacturing process. Soldering would also destroy the wax film. The cost of the wax used in coating the different sized cans was small, as Table I11 shows. These costs were based upon a price of 10 cents per pound for the wax. A low application cost for coating these cans will obviously depend upon a quantity demand for this type of container. Other products besides shellac varnish could probably be packaged to advantage in this type of coated can. Waxlined containers for beer are already commonly used. Double protection of the varnish is as-. sured by applying the wax to terne-plated containers. The extra protective coating can be applied as well to lithographed cans. - -
Acknowledgment The authors wish to thank those connected with the American Can Company for their cooperation in making this a complete study of the problem, and to express their appreciation to the Quaker Chemical Company and to the many can manufacturers who kindly supplied samples of their products and gave many helpful suggestions.
FOR LINING CANS TABLE111. COSTOF WAXREQUIRED
Size of Can Pint Quart 0 . 5 Gal. 1 Gal.
Av. Wt. of Wax, Grams 3 4
7
12
cost, Cent 0.066 0.088 0.155 0.286
1181
Literature Cited (1) De Sylva, O., thesis, Polytechnic Inat. of Brooklyn, 1932. (2) Verman, L. C., and Bhattacharya, R., London Shellac Research Bur., Tech. Paper 8 (1936).
PRESENTED before t h e Division of Paint and Varnish Chemistry a t the 96th Meeting of the American Chemical Society, Milwaukee, Wis.
SEPARATION PROCESSES Fractionation of Partially Miscible Liquids' MERLE RANDALL AND BRUCE LONGTIN University of Caliiornia, Berkeley, Calif.
The distillation of binary mixtures of the minimum boiling and the eutectic vaporization types is discussed. A design method is given for a particular type of equipment for such a distillation. The design method may easily be generalized to other types of equipment.
l-
N PREVIOUS papers (3, 4) general methods of analysis
of separation processes were presented. These methods are free from the restrictions of the usual simplifying assumptions. I n this paper an important application of these methods is discussed.
The molal heat content vs. mole fraction diagram for a twocomponent system which forms two partially miscible liquid phases a t the boiling point deviates widely from the conditions necessary for the application of the McCabe and Thiele methods of graphical analysis. Gay (1) gave a design method for a particular restricted case of distillation of such mixtures. This paper presents the introduction to a general analysis of all such separation processes.
Phase Diagrams for Partially Miscible Liquids The temperature 8s. composition diagram for vaporization of partially miscible liquids is quite familiar. As the upper portion of Figure 1 shows, it is analogous to the melting point diagram for partially miscible solids, which form a eutectic mixture (2). The analysis of the case that the eutectic temperature lies between the two boiling points will be treated in a later paper. 1 This is the aixth paper in this series. The first five appeared in September, October, November, 1938, and in February and July, 1939. respectively.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1182
The molal heat content vs. mole fraction diagram is not so well known. If we recognize that each liquid mixture, as well as each single liquid, must have a heat of vaporization, and that there is a heat of transition between the two liquid phases, it becomes obvious that the diagram must take the general form of the lower part of Figure 1. From the phase diagrams of Figure l it is apparent that the composition of a vapor is always nearer the eutectic value than that of the equilibrium liquid. I n so far as the vapor is concerned, the situation is that of a system having a minimum boiling mixture.
T
I
1
N=O
N=l
FIGURE 1. (Above) TEMPERATURE us. MOLEFRACTION AND (below) HEAT CONTENT vs. DIAGRAMOF MOLE FRACTION A PAIROF LIQUIDS,PARTIALLY MISCIBLEAT THE BOILINQ POINT
Simple Enriching Section Let us consider an
adiabatic simple column section (3) in which the reflux ratio is less than unity. For such a section the net flow point lies above the vapor curve. As Figure 2 shows, the graphical construction2does not differ from that for an ordinary pair of components so long as none of the liquid streams has a composition within the region of two liquid phases. However, since each vapor rising from a plate is nearer the eutectic composition (point J ) than the liquid flowing down from the plate, the vapor issuing at the top of the column is, in general, nearer to the eutectic composition than the vapor entering the bottom of the section. & Consider the case in which the liquid a t some point in the column section has its composition in the region of two liquid 2 The right-hand diagram of Figure 2 shows a n unusual state of operation of a simple enriching section. I n this case the liquid entering the top of the section is richer in more volatile (i. e., eutectic) component t h a n t h e vapor leaving the column. This condition may obtain with the use of top equipment of a type not yet discussed.
I
I
mu+1.
LV+IK
“”+‘ I
I n the case of a simple stripping section (in which the reflux ratio is greater than unity), the net flow point lies below the liquid curves, The same cases and same behavior arise, with one exception, I n the stripping section if L, lies in the region between I and K,and L,+1 does not, then the whole section, both above and below the vth level, must function in a retrograde fashion.
vu
!
phases. The phase point may, for instance, be LU(Figure 2). The liquid a t this point in the column consists of the two liquid phases, I and K , in the proportions of Z K moles of I moles of K phase. If the vapor rising through phase to the column a t this same interplate level is represented by the point Vu (it may come from equilibrium with a liquid which is not in the two-phase region), then we may determine the net flow point, D, from the reflux ratio a t this level. The vapor rising from the plate above the vth interlevel must come from equilibrium with liquid Lu. The only vapor which can be in equilibrium with either liquid I or liquid K , or both, is the “eutectic” vapor, J. Hence VU+^ lies a t point J. Liquid Lu+l must be represented by a point on line There are two cases which may arise, depending on ~ between I and K,or it lies the position of D. Either L P +lies outside of I T on the opposite side from VU. If L ~ lies + ~between I and K , then the liquid stream consists of I and K phases in the proportion moles of I phase of and moles of K phase. Vapor VU+Zcoming from equilibrium with liquid Lu+ can be only the vapor represented by point J . This serves to locate Lu+z as coinciding with L1+ v , and so on. As we proceed to higher levels in the column, we find that all of the vapor streams N=O N=l above VU have the comFIGURE 3. SIMPLECOLUMN SECTION WITH Two LIQUID position J , and all the PHASES(RETROGRADEENliquid streams have the RICHMENT IN TOPPART) same composition, Lu+l. The d a t e s above the vth level do not accomplish any useful purpose. In this case it is not possible to enrich any mixture beyond the two-phase region. The behavior is almost exactly that of a minimum boiling mixture. When Lu+l lies outside of J K , the stepwise construction may proceed regularly, as Figure 3 shows. However, it is readily seen that the upper portion of the column section is functioning in a retrograde manner. The difference in composition of liquid L u + zfed in a t the top and vapor Vu+l received is greater than the equilibrium separation. If the column section is equipped with either a total or a partial condenser returning reflux, it cannot possibly exhibit retrograde action. The line through the D point which represents the material balance a t the condenser must be vertical (4, and hence the construction must always fall in the first case. I n a n ordinary enriching section equipped with a condenser for returning reflux, it is impossible to carry enrichment across the region of two liquid phases, just as it is impossible to cross the composition of a minimum boiling point.
Simple Stripping Section
H
I
VOL. 31, NO. 9
I
LI y NIO N=l FIGURE 2. FLOWAND DESIGN DIAGRAMS FOR A SINGLB ENRICHING SECTION
Ordinary Continuous Rectification We may combine the above two units into the design for a n ordinary continuous rectification column with intermediate
SEPTEMBER, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
feed. The design for such a column (Figure 4)indicates that the top product will more or less approach the J (eutectic) composition, no matter what the composition of the feed may be. The composition of the bottom product will depend on whether the feed composition lies to the right or to the left of the eutectic point, and will lie on the same side of the eutectic. In no case will the composition at any level cross over the region of two liquid phases. If we attempt to accomplish such a result by increasing the number of plates in the top section, we succeed only in reaching the state in which at some plate in the section the liquid breaks into two phases. And on every plate above that level there are two liquid phases in such proportions that the gross composition of the liquid has a value equal to that of its equilibrium vapor, represented by point J.
1183
senting the vapors delivered a t the tops of the two columns. These vapors are used to heat the feed (the feed is used to condense the vapors) and produce a liquid mixture near the boiling point. This liquid constitutes the contents of the separating tank. It is the sum of the two vapors and the feed. The point representing it must lie a t the center of gravity of the three points, V,, V,’, and F’, and hence somewhere within the triangle defined by them.
Separation into Two Pure Components In order to obtain more or less complete separation of such a mixture into the two components, it is necessary to devise some special means of crossing the region of two liquid phases. The existence of an equilibrium separation between the two liquid phases offers a solution of the problem. If a t any point in the column we obtain a stream consisting of two liquid phases, we may remove that stream and separate the two phases. The compositions of the two phases, a t least at the boiling points, will lie on opposite sides of the eutectic vapor composition. From one phase we can prepare eutectic mixture and one pure component, and from the other, eutectic mixture and the other pure component. There are a number of possible schemes bv which this mav be accomplished. Witk;out attempting to correlate the design with any existing apparatus, we shall discuss several cases. Two COLUMNSWITH F E E DT O S E P A R A T O R TANK. The apparatus consists of two separate distilling towers, each with its own vaporizer. The vapors from the top of each tower are mixed together with the feed liquid, to obtain a nearly boiling I I mixture consisting of two N=O N=l liquid phases. The two FIGURE4. CONTINUOUS phases are separated, and RECTIFICATION OF A PARone phase is sent as reTIALLY MISCIBLE LIQUIDPAIR flux to each of the two Right, feed and end products towers. The flow chart outside two-liquid-phase range; and design diagram for left, top portion of enriching section with two liquid phases. this process are shown in Figure 5. The two towers behave individually as simple stripping sections. The addition which we have made to the usual stripping tower flow chart is the separating tank and the flow of streams through it, by which the two towers are interconnected. The over-all material balance of the process requires that the feed, F’ (the actual feed, F , plus the heat “fed” to the condensers) be the sum of the net flows, D and D‘, in the two towers, since the feed splits into these two net flows. Hence the points D , F’, and D‘ in Figure 5 lie on a straight line. The proportions of the two products, Lb and Lb‘,are indicated by the proportions into which the line DF’D‘ is divided. Suppose that we have carried out the stepwise constructions for the two stripping sections, using points D and D’ as net flow points, and have obtained points V , and V,’ as repre0
-
I=I
1=1
Hebt
I
N=I FIGURE 5 . FLOW AND DESIGN DIAGRAM FOR Two COLUMNS WITH FEED TO SEPARATOR TANK N=O
+ +
The point (8‘’ V , V,’) represents this sum for a case in which the two vapor streams contain about equal numbers of moles and the feed stream contains four times as many moles as either vapor stream. Actually it represents two liquid phases, L ,and L8‘,which lie a t the ends of the tie line on which it lies, and which represent the compositions of the two liquid phases returned as reflux. Liquid L, is returned to the column from which vapor V, was obtained. Streams L, and V , together define the net flow into the column, and hence these two points lie on a straight line through D. Similarly L,’ and Vt’ must lie on a straight line through D’. This completes the graphical construction. M I N I M U MB O I L I N G POINT JUST ABOVE A CRITICAL MIXING TEMPERATURE. A case which is very close to that just considered, although not common, is useful in obtaining a clearer picture of the graphical problem. This is the case in which the critical mixing temperature comes somewhat below the temperature of the b o i l i n g p o i n t , and the system possesses a miniFIGURE 6. DESIGNDIAGRAM mum boiling point, FOR Two COLUMNS WITH FEED The phase diagram for TO SEPARATOR TANK(CRITICAL MIXING POINTBELOW such a system is shown in MINIMUM BOILING POINT) Figure 6 . The chief difference between this and the previous system is that there is no region of three coexistent phases. The phase diagram typified by the lower part of Figure 1 may be considered as a special case in which the “dome” representing two liquid phases moves up into contact with the liquid-vapor area. I n an ordinary distillation of such a mixture there will be no formation of two liquid phases within the column section and none of the peculiar behavior made possible by the region of
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1184
ble to attain the desired stripping. As a previous paper (6) indicated, a n infinite number of plates is required to produce a sepa-
VOL. 31, NO. 9
occur when the tie line is just tangent to the curve bounding the region of two liquid phases. I n this case we merely draw the common tangent to the caustic curve and the two-liquidphase boundary. For the case shown, Lt, Lt’, the points of tangency do not lie a t the ends of an equilibrium tie line. If one of the column sections is operating a t maximum reflux, the liquid fed to it is of the composition represented by one of the points of tangency to the liquid-liquid curve. The liquid fed to the other column must come from equilibrium with that fed to the first and hence cannot be represented by the other point of tangency. Hence both columns cannot operate a t maximum reflux simultaneously except in unusual cases. However they may both operate very close to maximum reflux at the same time, since we see from Figure 8 that a v~ shift of the rays DV, slightand D’V,’ will bring intersections L, and Lt’ to the H ends of the same tie line. I n the case first discussed, in w h i c h t h r e e phases may coexist, it may happen that thereis no tie line tangent to the liquid-liquid curves (Figure 9). In this case the I tie lines J I and J K deP =O N=l fine the maximum reflux. FIGURE 9. CASE OF MAXIThe D point cannot lie MUM REPLUX WHEN No TIE above these extended tie LINES ARE TANGENT TO lines. LIQUID-LIQUID CURVES
Preheating of the Feed point. When D falls at this point, it will be just possible with an infinite number of plates t o obtain a bottom product of the desired
bT/ Mt
porizer ping section feeding with onevaof t h e two saturated liquid phases. This point locates the condition of maximum reflux for one of the
I n a case of either maximum or less than maximum reflux, point F’ representing the feed is determined by the graphical construction and the composition of the feed. It may happen that the temperature a t which the feed is received is such that its molal heat content is not that required by the graphical construction in order to give the desired products. If we fed the column with the liquid a t the temperature a t which it is received, the process would not operate as desired. Hence, if the feed as received has the heat content represented by F , it may be necessary to preheat the feed to the temperature required at point F’.
L /
-0
k?
,-- -- ----
j f’--
tF
Feed
actly the same Of FIGURE 8. COR’STRUCTION FOR condition holds for the MAXIMUM REFLUX USING THE other column, the posiCAUSTICCURVES tion being determined by the intersection of the tie lines with the vertical line representing the desired composition of the other product. CAusTrc CURVES. The actual calculation of the condition of maximum reflux can best be done with the help of the equilibrium caustic curves (Figure 8). These curves are constructed from equilibrium data in the manner indicated in a previous paper ( 5 ) . The equilibrium tie lines must be tangent to the caustic curve. We draw in the vertical line representing the composition of desired product. Then we lay a straight edge tangent to the caustic curve and, keeping it tangent, move it about until the position has been located a t which it passes through the two-liquid-phase area and cuts the vertical line in the highest point. Ordinarily this will
Condensation of Vapors Point F representing the actual heat content of the feed may lie too high, so that if we carried out the process unaltered, we would be operating above the maximum reflux ratio permissible for the desired separation. It then becomes necessary either to precool the liquid feed or to partially condense the vapors before mixing them with the feed. Of the two procedures, the latter is the most practical. That condensation of the vapors will serve the desired purpose is apparent from Figure 10. If vapors Vs and Vs’ received from the two columns are cooled, we obtain streams Vt+l and Vt+l’, which may be either partially condensed or actually cooled below their boiling point, entering the separator tank. The flow chart around the separator tank is shown a t the left of Figure 10. Streams Vt+1and L, determine a net flow which differs from the net flow into the top of the column only in the heat removed, and not in composition or net amount. This net flow, therefore, has the same composition as D and is represented by a point on straight line L,Vt+l-namely, point D t + l in
-
SEPTEMBER, 1939
1
INDUSTRIAL AND ENGINEERING CHEMISTRY -
F I
t
Heat
1185
I
vides a tremendous saving of heat. That is, without reheating, one would need to supply a t least the amount per mole represented by the distance from D,+l and Dtcl‘ to the vaporization curve, as against the much smaller values with reheating. But this is not true. I n the reheating we must supply heat per mole of liquid equal to the dis-
H
t
E :O N=l FIGURE10. FLOW AND DESIGNDIAGRAM FOR CONDENSATION OF VAPORS FEDTO SEPARATOR TANK
Heat
+ *
F
Heat
1
Figure 10. Similarly, the two streams Lt’ and VS+~‘ determine the net flow point Dt+l’. The material and heat balance of the separator tank gives I.. s o N: I the feed, F , as the sum of the net flows D,+l and D ; f l r . It is not the sum of D and D‘, but differs from this sum by the FIGURE11. FLOWAND DESIGNDIAGRAM FOR CASE OF amount of heat removed in the condensers. It is now the REHEATING LIQUIDS FROM THE SEPARATOR sum of streams F, V;+1, and Vt+1’ that determines the gross composition of the combined liquid streams leaving the sepatances Lt+lLt and Lt+l’L;’, respectively. But from the gerator. ometry of the center-of-gravity property, the numbers of The completed diagram of Figure 10 shows that condensamoles in the two streams and Dt+l are just inversely protion of the vapors produces an effect equivalent to precooling portional to the distances and Dt+,Dt, so that the total the feed. I n order to obtain the desired products efficiently, heat used in reheating is just equal to the difference between it may have been determined that the reflux ratios in the two the total amounts needed a t the still with and without reheatcolumns must be those associated with the net flow points, ing. I n other words, there is exactly no saving. The only D and D‘. With condensation we may achieve these reflux difference due to reheating lies in the way the steps are conratios with the feed a t a temperature corresponding to point structed. F . To obtain this result without condensation, we must preIt is apparent that in this case condensation of the vapors cool the feed to a temperature corresponding to point F‘. may be desirable. The analysis may be treated in the same REHEATINQ OF LIQUIDS. I n this process both columns are way by the use of net flow points Dt+l and Dt+l’ now deteroperating as stripping sections and hence deliver product a t mined by the point pairs (Lt+l, Vt+J and (Lt+l’, Vt+l’). the greatest rate when the reflux ratio is large. It is desirable The chief advantage which may accrue from reheating the to operate them a t as large a reflux ratio as possible. Particuliquids is as a means of utilization of the heat of condensation larly in the case that the system does not give three coexistent of vapors through the use of heat exchangers. phases it may be possible to increase the limiting reflux ratio considerably by reheating the liquids from the separator before returning them to the columns. Optimum Location of Feed Stream Let us consider a case in which both liquids are reheated to The process which we have so far considered is Darticularlv their boiling points, while the vapors are condensed only by suited to the tieatment i f addition of the feed. We feed materials whose commay graphically represent positions lie in the region of t h e material and heat two liquid phases. When balances around the sepathe feed composition lies rator by the device (that outside this region, it may we used for condensation) be desirable to enter the of net flow points Dt+l and feed elsewhere than in the Dt+1’ for the streams lying separator tank. By so dobetween the heaters and the ing we lose the advantage seDarator tank. The reof direct heating of the feed sulting diagram is obviously by c o n d e n s a t i o n of the that of Figure 11. vapors, but we may accomSince the distance from plish practically the same points Dt and Dt’ to the F result with a heat exchanger. liquid vaporization curve The design diagram for measures the amount of this case is shown in Figheat that must be supplied ure 12. Starting from the to the still pots per mole of bottom of the column in each product withdrawn, 1 I I Heat Heat N=O N=l which the feed is introduced, Figure 11 would seem to it proceeds just as for an show a t first sight that FIGURE12. Two COLUMNS AND SEPARATOR TANK (FEED ordinary continuous rectiSTREAM IN SIDEOF ONE OF THE COLUMNS) preheating the liquids pro-
m
-
f
4%
1186
INDUSTRIAL AND ENGINEERING CHEMISTRY
fication column, including the feed plate construction, until the top of the tower is reached. At this point vapor Vt is condensed (as Vt+l),is mixed with condensate Vt+,’ from the other column, and splits into two phases, Lt and Lt’. Point X , the sum of and Vt+l’, is also the sum of Lt and Lt’. From here the construction proceeds as before. Many of the behaviors which we have found for the column with feed a t the separator tank have their analogies in this process. They may easily be studied by the procedures already used.
VOL. 31, NO. 9
Clerical assistance of the Works Progress Administration is gratefully acknowledged (0.P. No. 665-08-3-144). Bruce Longtin, the junior author, is the Shell Research Fellow in Chemistry at the University of California.
Literature Cited (1) Gay, “Distillation et Rectification,”Paris, Bailliere et Fils, 1936. (2) Randall and Avila, unpublished data. (3) Randall and Longtin, IND.ENQ.CHIM.,30, 1063 (1938). (4) Ibid., 30,1188 (1938). (5) Ibid., 30, 1311 (1938).
CORRESPONDENCE Deposition of Gold on Fabrics AND ENGINEERING CHEMSIR: The reference in INDUSTRIAL [31,5 (1939)l to my process for the deposition of films of pure gold a t the ordinary temperature on a variety of surfaces, including those of glass, silica, porcelain, metals, plastics, textiles, etc., which was discussed by Ernst A. Hauser [31, 650 (1939)l is inaccurate. The inaccuracy first appeared in an article in the New York Times of August 29, 1938, in which an account is given of my presidential address on “Recent Advances in the Chemistry of Gold” to the Chemistry Section of the British Association for the Advancement of Science. My address was followed by a demonstration on the “Production of Gold Films by Chemical Methods” treated historically, as far as this could be done in an hour and a half. Gold films produced by chemical methods were probably first used for the decoration of pottery and porcelain, and this was effectively demonstrated by H. V. Thompson. Such a method involving high temperatures restricts the type of surface to which the film can be applied; but it is of interest that Faraday also prepared gold films on glass surfaces by gently heating the dry residue obtained by evaporating aqueous solutions of hydrochloroauric acid. Mann (3) recently described the trialkyl phosphineaurous and trialkyl arsineaurous halides, which have the general formula: RsP(As) -P AU - X where R = alkyl and X = halogen ISTRY
Certain of the phosphorus compounds especially are readily volatile, and when their vapors are heated, preferably under reduced pressure, they yield gold films which are deposited on the glass wall of the containing vessel. Mann illustrated this process of producing gold films which is similar to their production by heating the interesting dialkyl acetylacetone gold compounds (2) having the general formula: 0-C(CHa) O=C(CHs)
At the demonstration it was pointed out that the production of gold films a t the ordinary temperature was probably first carried out by a Monsieur Sage who is referred to by Mrs. Fulhame in her book “An Essay on Combustion with a View t o a New Art of Dyeing and Painting Wherein the Phlogistic and Antiphlogistic Hypotheses are Proved Erroneous.” (The author presented a copy to the Royal Society of London on January 28, 1795.) Mrs. Fulhame’s work is based on that of Monsieur Sage who showed that hydrochloroauric acid is reduced by
phosphorus; she clearly describes methods by which the gold film can be deposited on silk and other surfaces, Mrs. Fulhame’s results are not only of great interest in themselves but have the added importance of being the basis of experiments carried out by Faraday in 1856 on the production of gold films with a view to the examination of their optical and other properties, For the production of his gold films Faraday also used phosphorus as the reducing agent of hydrochloroauric acid in what he described in his diary on April 21, 1856, as “this long and as yet nearly fruitless set of experiments on gold.” Other methods for the production of gold films a t ordinary or slightly elevated temperatures, which depend on the use of reducing agents (for example, hydrazine), have also been described. The basis of the new method ( 1 ) for the production of flms of pure gold at the ordinary temperature and depositing them on various types of surfaces is to allow certain classes of organic gold compounds to decompose spontaneously when dissolved in a suitable solvent in the presence of alkali. Among the gold compounds which may be used are those of the type: R X R R where R = alkyl,aryl, and X
=
X R halogen
In the actual demonstration it was possible to show the deposition of the gold film only on various glass surfaces, but specimens of the deposition on a variety of surfaces, including textiles, were on exhibition. The statement that trialkylphosphine aurous halide is the gold compound used in the new process for the production of flms of pure gold and their deposition on a variety of surfaces is an error for which I am not responsible since I did not see the original newspaper report before it appeared in print. This error has been repeated many times in the popular press. It has caused considerable confusion. Perhaps the wide circulation of INDUSTRIAL AND ENGINEERING CHEMISTRY may prevent the error from being perpetuated.
Literature Cited (1) Gibson, U. S. Patent (pending); British Patent, 497,240 (1938). (2) Gibson and Simonsen, J . Chem. SOC.,1930, 2531; Brain and Gibson. Ibid., 1939, 762. (3) Mann, Wells, and Purdie, Ibid., 1937, 1828.
C.8.GIBSON
GUY’SHOSPITAL MEDICAL SCHOOL UNIVB~RSITY OF LONDON LONDON S. E. 1, ENQLAND June 2, 1939
