J a n . , 1917
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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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relatives. T h e ferrous silicates are green, t h e ferric, yellow. Copper glasses, when t h e batch contains a n oxidizing agent, are blue a n d here again t h e color is t h e same as t h a t imparted t o a dilute aqueous solution b y t h e cupric ion. T h e color imparted t o glass by cobalt oxide is practically identical with t h a t produced by a n excess of concentrated HC1 in aqueous CoClz solution where t h e complex CoC14 is supposed t o form. The color of vitreous manganese solutions resembles t h a t of aqueous solutions. Similarity in valence was recently shown by Scholesl in his article on “Trivalent Manganese in Glass.’’ In opal and alabaster glasses we encounter another striking parallel t o conditions in aqueous solutions. Opalescence is largely due t o finely divided alumina of colloidal size. Just as electrolytes will precipitate such colloids from aqueous solutions, so NaCl or NazSOl or other chlorides or sulfates will precipitate this colloid from vitreous solution. As a result, a glass which is opalescent without t h e addition of one of these salts becomes a n alabaster glass if t h e y are added, through t h e precipitation of t h e colloid b y t h e salt. The light t h e n transmitted is white. When t h e sulfate ion is present t h e color is more intense t h a n with t h e chloride ion. Effects resembling t h e Liesegang layers have been obtained in opal glasses t o which COO a n d selenium were added. T h e alternating s t r a t a are blue a n d white when t h e glass gathered from t h e pot is allowed t o cool without reheating. CONCLUSION
The d a t a presented seem t o indicate clearly t h a t much might be accomplished b y studying vitreous solutions, in part a t least, on t h e basis of similar phenomena observed in aqueous solutions of some of their constituents. T h e writer hopes t o a d d evidence through researches which are under way and planned. SCHOOL OF CHEMISTRY UNIVERSITY O F PITTSBURGH PITTSBURGH
CHEMICAL COMPOSITION vs. ELECTRICAL CONDUCTIVITY2 By COLING.FINK
Some years ago, while still a t t h e university, I carried out a number of experiments on t h e electrothermic production of ultramarine. Powdered mixtures of sodium sulfide, china clay a n d carbon were interposed between carbon electrodes in a closed crucible furnace. I observed a t t h e time t h a t in order t o keep t h e electrical resistance a n d t h e temperature of t h e charge fairly low so as t o avoid decomposition of t h e ultramarine as soon as i t was formed, i t was necessary t o use very finely divided carbon, such as lampblack. With charges made u p of powdered coke which was coarse compared t o t h e lampblack, I could THISJOURNAL, 7 (1915), 1037. Presented at the 53rd Meeting of the American Chemical Society, New York City, September 25 to 30, 1916. 1
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not get a n y appreciable current t o pass between t h e carbon electrodes u p t o potentials of 2 jo volts. Subsequently, I have found repeatedly t h a t t h e electrical conductivity of mixtures of finely divided substances is a function of t h e relative size of t h e components. E X P E RI h.1 E NT A L
A series of tests was made in order t o get values of a more quantitative nature. Two substances were selected, t h e physical properties of the one as divergent as possible from those of t h e other: a black metal powder, tungsten, and a white insulator powder, thoria. The advantages in this selection are manifold; both tungsten and thoria will stand very high temperatures and can therefore be made practically moisture-proof. I t is a well known fact t h a t in all high-resistance tests adsorbed moisture is a very disturbing factor. Metals such as copper and silver were not serviceable since they cannot be heated to high temperatures without partial -qaporization, which though slight was sufficient to cover the surface of t h e insulator granules with a highly conductive film. Other factors that decided our selection in favor of tungsten a n d thoria were: ( r ) high state of purity; ( 2 ) availability of both in extremely fine powdered form (readily sifted through 2 j o mesh gauze); (3) constancy and stability under ordinary atmospheric conditions; (4) sharp distinction in color; ( 5 ) high specific gravities (which reduced t h e tendency t o dust). All mixtures here recorded were made up of equal weights of tungsten a n d thoria. As regards t h e size of the particles, as stated above, t h e mixtures would pass readily through silk having 2 5 0 meshes t o t h e inch. The holes in this silk are about 0.001 in. in diameter. All attempts t o segregate particles of a well-defined size by such methods as suspending water, organic liquids or air, were frustrated o n account of t h e persistent tendency of t h e very fine particles t o form agglomerates. We finally resorted t o t h e familiar “ t a p test.” This gave us fairly good comparative values of t h e fineness of t h e various powders used. T e n grams of t h e powder or powder mixture were filled into a I O cc. glass graduate a n d tapped t o constant volume; usually, after 7 minutes no further decrease in volume could be detected. The ultimate volume in cc. divided by I O gave us t h e relative volume (vr) as recorded in Table I. It can easily be demonstrated t h a t t h e values for ZJ, are a function of t h e density a n d mean particle size. At first there seemed t o .be a serious objection t o t h e t a p test, namely this, t h a t a powder composed of, say, equal parts of coarse and fine particles would give t h e same figure for vr as a second powder whose particle size was a mean between t h e two limiting sizes of t h e first powder. This objection t o t h e t a p test was automatically set aside since in t h e ordinary preparation of metal or oxide powders in single small lots b y far t h e greater majority of particles are approximately of t h e same size. This tendency t o f o r m a ‘Lstandard”size is a universal phenomenon, t h e dimensions of a n y particular standard
