Jan., 1917
T H E J O U R N A L OF IA’DUSTRIAL A N D ENGINEERING C H E M I S T R Y
same phosphoric acid solution, if all were volatilized a n d precipitated, would amount t o 0 . 7 5 per cent. Since t h e amounts of hydrofluoric a n d sulfuric acids found even in Solution A form only a comparatively small p a r t of t h a t which would be present in t h e phosphoric acid if all were volatilized a n d precipitated, i t is evident t h a t under t h e conditions of t h e precipitation t h e greater part of t h e hydrofluoric a n d sulfuric acids pass thr,ough t h e apparatus in t h e form of gas a n d are therefore not acted upon by the precipitator. The acid collected when t h e fum-es were passed through t h e baffle tower contained in suspension a slight amount of insoluble material consisting mostly of volatilized silica, b u t when this was removed by filtering, or by decantation on settling, t h e acid obtained was then perfectly transparent. When t h e baffle tower was cut out, t h e acid collected naturally contained a larger amount of suspended matter with a consequent small increase of bases in solution and was somewhat colored, due, no doubt, t o carbonaceous matter carried over with t h e current of air. By operating t h e furnace continuously a n d by reducing t h e amount of heat radiated, i t should be possible t o pass t h e fumes from t h e furnace through a n efficient baffle tower and yet make t h e precipitation a t temperatures above 100’. Judging from t h e results already obtained, t h e acid collected under these conditions should be of sufficient purity for use in those industries where a relatively pure acid is required. T o prevent contamination of t h e acid in its preparation t h e precipitator must be made of stoneware or porcelain and all metal must be avoided in all parts of t h e equipment t h a t come in contact with t h e fumes. I n t h e manufacture of phosphoric acid for use in fertilizers these special precautions for collecting pure acid would of course be unnecessary. s u M JI A R Y An investigation on a semi-commercial scale has been made of t h e use of t h e Cottrell precipitator in recovering t h e phosphAric acid evolved in t h e volatilization method of treating phosphate rock by ignition with coke a n d silica in a n electric furnace. A current of air which was passed over t h e charge in t h e furnace served t h e double purpose of oxidizing t h e fumes of phosphorus t o phosphorus pentoxide a n d of carrying t h e latter t o t h e precipitator. I n one series of experiments t h e fumes from t h e furnace before entering t h e precipitator were passed through a tower provided with baffle plates which had t h e effect of cooling down t h e gases t o about ordinary temperature. I n a second series of experiments the tower was cut out a n d t h e fumes passed almost directly into t h e precipitator a t a temperature above 100’. I n each case t h e phosphorus pentoxide, which takes up water from t h e current of air passing through t h e furnace a n d also from t h e moisture driven off from t h e charge, is precipitated in t h e form of a solution of phosphoric acid. When t h e precipitation is made a t temperatures of about IOO’, or above, t h e concentration of t h e acid is greater t h a n t h a t collected
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a t a lower temperature, b u t b y reducing t h e flow of air through t h e furnace, acid of high concentration may also be obtained with low temperature precipitation. T h e advantages of this method of collecting t h e phosphoric acid over t h e scrubbing tower method now in use are as follows: I-The equipment required is simple in construction a n d automatic in operation. 2-The simplicity of t h e construction of t h e precipitating pipes decreases t h e difficulties arising from t h e corrosire action of t h e phosphoric and hydrofluoric acids evolved from t h e phosphate rock. 3-In this way there may be recovered phosphoric acid of a high degree of purity suited for direct use without further purification in those industries where a relatively pure acid is required. 4-A more concentrated acid can be obtained in this way t h a n is possible t o prepare directly by a n y other commercial process, and when this acid is used in t h e preparation of concentrated fertilizers, such as mono-ammonium phosphate, a dry product may be obtained directly without t h e necessity of evaporating solutions, or of drying t h e resultant product. This is t h e first time t h a t t h e Cottrell precipitator has been used for t h e precipitation of a product which has been purposely volatilized with a view t o its recovery in this way. BUREAUOF SOILS IJ. S. DCPARTMEKT O F AGRICULTURE WASHINGTON, D. C.
EMULSIONS AND SUSPENSIONS WITH MOLTEN METALS’
,
By H. Vi. GILLETT?
The object of this paper, which is written a t Prof. Bancroft’s request, is not t o present any new information, b u t t o suggest a line of thought. I n t h e refining of aluminum chips t o ingot a loss of 30 per cent of t h e metallic content is common a n d a 1 5 per cent loss represents very good practice. I n a study3 of these losses i t was found t h a t t h e cause for t h e high loss is not primarily t h e ease of oxidation of aluminum, but the failure of t h e globules t o coalesce; t h a t is, t h e loss is not due t o oxidation in the furnace unless abnormally oxidizing conditions obtain there, and is not preventable b y retorting, vacuum furnaces, electric furnaces, etc. Commercia1 aluminum chips from t h e machine shops of t h e automobile manufacturers contain about 2 0 or 30 per cent of t h e total weight t h a t will pass a ao-mesh sieve a n d are about 0.00j in. thick. There is usually not less t h a n 3 per cent and sometimes ~j per cent of cutting oil or compound and usually not less t h a n j per cent and sometimes I j per cent of very fine dirt, such as floor sweepings mixed with t h e chips. If one tries to melt down aluminum chips in t h e way brass chips would be melted, t h e larger a n d thicker 1 Presented a t the 53rd Meeting of the American Chemical Society, New York City, September 25 to 30, 1916. 9 Published by the permission of the Director of the Bureau of Mines. H. W.Gillett and G. hl. James, “Melting Aluminum Chips,” Bureau of Mines, Bull. 108 (1916).
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
chips melt down t o fairly large globules t h a t succeed in breaking throtigh the skin of dross, getting into true metallic contact with each other and coalescing into a pool of metal t h a t can be poured satisfactorily. But the tiny droplets formed by the melting of the smaller chips are so microscopic in size and so infinitely light in weight t h a t they cannot break through t h e honeycomb of oxide and dross about them. So, instead of going down where they are wanted, they remain in the dross. I n order t h a t as many of t h e medium sized drops as possible may not be too viscous t o flow down, t h e temperature is raised far above the melting point. When the very hot dross, which is dry and powdery, is skimmed off and reaches t h e air, t h e tiny entangled globules burn up a t once, with a thermit-like behavior. The pool of coalesced metal, even in the open air, takes on a thin coat of oxide which then protects it from further oxidation. So while oxidation (and nitridation as well) is the ultimate cause of t h e loss, this oxidation would not t a k e place save for t h e very finely divided physical state of t h e metal. f. Two methods serve t o reduce the loss by promoting coalescence, and both are in commercial use, though t h e details of t h e methods appear t o be known only b y a few refiners. One is the “puddling” process where t h e chips are melted in an open iron pot, small amounts being added a t a time, and each addition being thoroughly stirred and pushed into t h e main mass, t h e temperature being very carefully kept only just above t h e melting point, so t h a t t h e mass is pasty, b u t not truly fluid. By the constant working over of t h e mass, the tiny globules are squeezed together with enough force t o break the entangling film and bring them into metallic contact. Finally, after t h e mass of metal surrounds t h e particles of dirt a n d oxide instead of the honeycomb of dirt surrounding the globules, i. e., t h e disperse phase of t h e emulsion-using this term loosely t o include suspensions also-has been reversed, and the mass is heated up so t h a t t h e dross will rise. The other method is t o mix large amounts of NaCl with the chips, as a menstruum to dilute or soak up t h e envelope phase of dirt, preferably using with t h e NaCl a small amount (say 1 5 parts to 85 parts of NaC1) of some fluoride, such as CaF2, t o dissolve t h e little AlZO3 present and heating without much stirring. This method also breaks up t h e emulsion and t h e tiny globules settle satisfactorily. Of course t h e best method is one of prevention, t h a t is, collecting t h e chips without contamination by dirt. Removing the dirt by washing and screening is possible, b u t troublesome and expensive. There are many other cases where a molten metal or alloy forms a n emulsion or suspension with a solid, a liquid or a gas. “Floured” or “sickened” mercury, where globules of mercury refuse t o coalesce when coated with talc, graphite, grease, etc., is one, and dirty molten sodium, another example of a liquid and a solid. Blue powder is a n interesting example, and t h e problem of
Vol. 9, No.
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melting it is quite analogous t o t h a t of aluminum chips. Roeberl distinguishes between ‘(physical” blue powder, or “zinc snow,” which consists of particles of zinc uncoated by foreign materials, and which coalesces on melting, and “chemical” blue powder, in which each particle is coated with a skin of ZnO and probably a little SiOz. The methods of separating t h e phases in this case are, distilling the volatile zinc away from t h e non-volatile impurjties, heating under pressure, t o break up the enveloping skin, as in t h e old hlontefiore system, or dissolving off the skin by the process of ‘Bleecker,2 who adds t h e blue powder t o an electrolytic bath of fused ZnCln kept above t h e melting point of zinc. The ZnClz has some solvent action on t h e coating and t h e particles migrate t o the cathode and coalesce. Another case where a small amount of a solid phase distributed through, or emulsified with a p o l t e n metal, is in defective fusible boiler plugs, where Burgess and Mericaa find t h a t a network of oxides may prevent t h e plug from blowing out although t h e metal of t h e plug is fully molten. Entangled oxides, t h e bane of t h e foundryman in steel, brass, bronze, and aluminum, are, in a sense a t least, emulsions of a solid phase with t h e liquid metal which are not broken up, b u t freeze into place and result in unsound castings. Here one either reduces the oxide chemically or attempts t o collect it in a slag by means of some flux. The retention of metal b y slag in reduction and refining processes is a case of a n emulsion of two liquids. I n t h e Pattison process we have another case where t h e breaking of the emulsion is essential. Metal fog in the electrolysis of fused salts is still another example. Richards* has recently brought this out in t h e cases of strontium and cerium. The emulsion of a gas in a metal gives rise t o a problem no less serious t o t h e foundryman t h a n t h a t of a solid or a liquid with t h e molten metal, for if t h e emulsion is not broken, we have blowholes and porous castings. Sometimes it is desirable t o maintain a n emulsion or suspension of a metal with another phase. Examples of a suspension of some solid with a liquid metal (or, more strictly, of a solid with a plastic mixture of solid eutectic and liquid metal) are t h e “near alloys” of Friedrich6 where such materials as cobalt silicate are mixed with a n alloy of goSn IOCU kept within the eutectic range. Here ,the cobalt silicate is probably t h e disperse phase. But there are useful cases where t h e metal is t h e disperse phase within a solid. I n sherardizing, zinc dust coated with enough oxide t o prevent coalescence is a necessity. I n calorizing, aluminum oxide is mixed with the aluminum powder for E. F. Roeber. Met. & Chem. Enp.. 10 (1912), 451. W. F. Bleecker, “The Electrolytic Method for the Reduction of Blue Powder,” Trans. A m . Electrochem. Soc., 2 1 (1912). 359. 8 G. K. Burgess and F. D. Merica. “An Investigation of Fusible Tin Boiler Plugs,” Trans. A m . Inst. Metals, 9 (1915). advance copy, 3 Pp. 4 J. W. Richards, “The Metallurgy of the Rarer Metals,” Met. & Ckem. Eng., 16 (1916), 26; THIS JOURNAL, 8 (1916), 736. ’ I K.Friedrich, “Near Alloys,” Met. €9Chem. Eng., 8 (1910), 191. 1 2
J a n . , 1917
T H E JOURiTilL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
t h e same purpose. Here a n “emulsion” of solid metal a n d solid oxide, if t h e process is run below t h e melting point of t h e metal, is required t o prevent t h e welding together of clean metal surfaces below t h e fusion point of the metal, or one of liquid metal a n d solid oxide t o prevent coalescence of t h e globules. if r u n above t h e fusion point. Emulsions of t w o liquid metals find a notable example in t h e mixture of half copper a n d half lead used for packing bearings, brake bands, etc. Molten copper a n d lead, in equilibrium, form a ta-o-liquid layer system, being immiscible. Yet i t is possible, by t h e use of sulfur or nickel as a n emulsifying agent, t o produce a quite uniform mixture of t h e two metals, though i t is as ticklish a job as t h e foundryman often attempts. T o a lesser degree, t h e liquation of lead or of some other low melting, immiscible phase in brass a n d bronze casting, offers t h e same problem. Could we obtain stable emulsions of metals normally immiscible in t h e liquid state surely some of them, after solidification, would be industrially useful. Useful emulsions of gases with metals are hard t o find. Yet uniformly porous metals or alloys might be useful. Hannoverl has shown t h a t lead, made porous by a n indirect method, makes a storage battery of four times t h e capacity for t h e same weight as one with solid lead plates. The chemistry of colloids is proving of immense use t o industry. I t is right t h a t t h e colloid chemist should deal with t h e system water, benzene, soap a t room temperatures a t t h e s t a r t , for seldom is much gained by attacking t h e more complicated problems before t h e simple ones are solved. Yet when he has flocculated a n d peptized. frothed a n d floated, long enough t o bring some semblance of order out of chaos a n d t o get some working hypotheses on t h e mechanism and causes of emulsions and suspensions, he may find i t of use for t h e clarification of t h e present somewhat emulsified theories, as well as of practiral value, if he will remember t h a t there are other systems t h a n water a n d oil and other temperatures t h a n o t o 100’ C. Molten metals a n d alloys, from mercury to tungsten, also offer their problems of colloid chemistry. And when t h e colloid chemist shall have solved only a few of t h e problems waiting for him in t h a t field, t h e foundrymen a n d metallurgists, a t least, will rise up a n d call him blessed. MORSEHAIL NEW Y O R K
ITHACA,
SIMILARITY OF VITREOUS AND AQUEOUS SOLUTIONS* I3y ALEXANDER SILVERMAN Received September 29, 1916
T h e striking similarity of properties of vitreous a n d aqueous solution, both as t o appearance a n d behavior, has led t h e writer t o refer t o t h e m frequently in lectures on glass. They are collected here as an introduction t o a series of papers, covering researclfes on individual cases, which will appear from time t o time. 1 H. I. Hannover, “The Production of Porous Metals,” Me1 & Chem. E n g . , 10 (1912), 509. * Presented at the 53rd Meeting of the American Chemical Society, New York-City, September 25 to 30, 1916.
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Zsigmondy, in his work on “Colloids and t h e Ultramicroscope,” calls attention t o t h e size and properties of small particles in solutions. When gold is introduced into t h e batch as element or in compounds, t h e melt results in a yellow vitreous solution resembling aqueous solutions of t h e chloride. When t h e glass is reheated t h e unstable compound breaks up and t h e red colloid results. This again resembles t h e aqueous solution in appearance. If reheated a number of times t h e glass mass becomes brown by reflected light a n d blue by transmitted light, just as t h e oxalic acid reduction of a n aqueous chloride solution yields a brown precipitate and blue supernatant liquid. T h a t t h e particles are of colloidal size is evident from t h e researches on glass b y Siedentopf a n d Zsigmondy. 1 Copper is introduced into t h e batch as CUSO or CuO or as a cupric salt. Reducing agents are added. T h e resulting glass resembles aqueous solutions of cuprous salts in appearance. On reheating, t h e glass turns red and with continuous heating and greater reduction i t assumes a liver-color. As in gold solutions t h e red color is due t o t h e colloid; t h e liver or red-brown mass consists of t h e coarser precipitate.2 Selenium enters t h e batch as element, sodium selenite or sodium selenate, together with a reducing agent. The resulting vitreous solution is black while hot and changes t o a colorless, yellow, red, or dark mass on cooling, depending upon t h e quantity of selenium present. When t h e colorless or light solution is heated i t again turns dark and if t h e correct amount of selenium is present becomes red on cooling. Fenaroli3 has shown t h a t t h e red solution consists of polyselenides resembling t h e polysulfides in sulfur-amber glasses. The writer examined some selenium ruby glasses for colloids while t h e Fenaroli experiments r e r e under n-ay, because of t h e similarity of behavior of gold, copper and selenium glasses on heat treatment, but found no obstruction t o t h e passage of light rays in t h e ultramicroscope. X peculiar fluorescence or bloom on t h e surface of t h e glass prior t o reheating was attributed t o partial reduction of zinc compound, as t h e glasses were high in zinc. This cloud, which Fenaroli subsequently examined ultramicroscopically, proved t o be colloidal selenium compounds which in t h e presence of reducing agents or on reheating in a reducing flame formed polyselenides with t h e alkalies in t h e glass. -4s cadmium sulfide is introduced into t h e batch, there is a possibility also t h a t selenium may go into solution in t h e sulfide or sulfides formed from this b y other ingredients of t h e batch. One chromium boro-silicate glass which t h e writer prepared transmits green light through a single layer and dark red through a double thickness. The colors resemble those transmitted by aqueous solutions of chromic chloride, which in a single thickness of dilute solution is green and in a double thickness dark red. Vitreous solutions of iron also resemble their aqueous Annat. phys., 10, 33. Paal and Lenze, Ber., 39, 1550. 8 Sprechsaat, 46, 658; Chem.-Zentr., 36, 1149.
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