INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1933
(3) Cheneveau, C., and Audubert, R., Compt. Tend., 168,553, 684 (1919). (4) Gans, Ann. P h y s i k , 37, 881 (1912). ( 5 ) Gans, Ibid., 47, 270 (1915). (6) Gehlhoff, G., Kalsing, H., and Thomas, hl., 2. tech. P h y s i k , 12, 323-44 (1931). (7) Hampton, W. M., J . Sac. Glass Tech., 16,401 (1932). (8) Kitaigorodsky, I., and Kurovskaja, S. I., Ibitl., 16, 210-18 (1932). (9) Lax, C., Pirani, M., and Schonborn, H., Licht zind L u m p e , 17, 173-6,209-12 (1928). (10) Mie, Gustav, Ann. P h y s i k , 25,337 (1908).
(11) (12) (13) (14)
(15) (16) (17) (18) (19)
833
Morey, G. W., IND. EXG.CHEM.,25, 74% (1933). Kacken, S . ,Juhrb. Miner,, 2, 133-64 (1915). Rayleigh, P h i l . Mug., 47, 375 (1899). Rayleigh, Proc. Roy. Sac. (London), 90A,219 (1914). Ryde, J. W., and Cooper, B. S., Ibid., 131A,451-75 (1931). Ryde, J. W., and Y-ates, D. E., J. Sac. Glass Tech., 10, 274-94 (1926). Schuster, A , , Astrophys. J . , 21, 1 (1905). Tammann, G . , "Kristallisieren und Schmelzen," L e i p i g , 1903. Zachariasen, IT. H., J . Am. Chem. Sac., 54,3841 (193%:.
RECEIVED April 8, 1933.
Chemical Analysis of Glass G. E. F. LUNDELL,Bureau of Standards, Washington, D. C.
C
HEMICAL analyses of glass differ from those of metallurgical materials in that they have always been restricted to production rather than purchase. In other words, glass is sold on physical rather than on chemical requirements, and the needs for analyses are those connected with the control of manufacturing operations, investigations of glasses (ancient and modern), or researches. This is probably just as well, for one can imagine the perturbation of the glass manufacturer if consumers should start investigating the arsenic content of bottles and glasses or the lead content of cut-glass bowls, as they do with sulfur and phosphorus in steels.
EARLY ANALYSES When chemical analyses of glass were first made, and this was not so long ago, the glass analyst's problem was not different from a type of analysis with which he was already familiar-namely, the analysis of rocks-for the earlier glasses were of the soda-lime-silica type. As for the methods of analyses, these were not very different from those we now use, except that the analysts worked under greater difficulties. Some typical analyses are shown in Tables I to 111. TABLE
I. WEISSESGLAS(1)
ROHREN LEICHTBENEDIQ FLUSBIQER B ~ E M E N FEUCH-ROHRENALS DAS QEI EMOURS "AUBBERORTIQKEIT "IN VOLLE W ~ H N L I C H W u"SEHR DENTLICH W E I M Q E R RdHREN WEI0SE WEISS" SCHON" ANZIEHT" QEZOQEN" G~as"
Kieselerde (SiOz)
0.720 Kalk (CaO) 0.064 Kali (Kz0) Natron NazO) 0:iiO Bittererie ( M ~ o ) . Alaunerde (Ah03, TiOz e t c ) 0.026 Eisenokyd iFezOs) 0.011 Blanganoxyd (MnO) .
..
Bloioxvd _ I - . (PbO) -
.....
__-
0 991
Silire (SiOz) Chaux (CaO) Alumine, oxydes de fer et de manganese (41203, Fez&, MnO) Soude et potasse (NazO KzOL
+
(In . .Der cent) 6i.4 66.7 66.0 2.7 5.8 7.2
Kieselsaure (SiOz) Thonerde (A1203, TiOz, etc.) Kalkerde (CaO) Magnesia (MgO) Kali (KzO) Natron (NazO)
71.23
69.4 6.4
69.4 7.1
2.8
3.0
5.4
4.5
2.9
2.8
24.7
23.8
24.5
16.7
21.3
20.7
100.0 100.0
100.0
100.0
100.0
- - - - - 100.0
TABLE111.
70.9 7.9
BEWARRTE
GLASER(6)
(In per cent) (Fenster Glaser) 71.03 71.92" 73.35a 72.68"
72.66"
1.70 16.39 0.20
2.98 15.62 0.15
0.85 13.65 0.16
0.73 11.91 0.71
1.06 12.76 0.26
0.95 15.20 0.25
10.78
10.76
13.42
13.12
13.24
10.94
....
....
....
....
....
I . . .
Summa 100.30 100.54 100.00 100.00 100.00 100.00 5.2:l: 4.4:l: 4.0:l: 4.2:l: 4.8:l: 5.3:l: SiOz:CaO.KzO 0.9 0.6 0.88 0.9 M g 0 ' Nag0 0.6 0.6 Kieselsaure als Rest (Analyse mittelst Flussaure)
0.015 0,010 0.010
0.012
0 993
0 991
SAMPLING The glass analyst does not meet with the difficulties that attend the sampling of fabricated products such as irons, steels, brasses, and bronzes, for he works with a homogeneous product. There is, however, one source of error that should receive consideration-namely, the change that takes place in samples of glass during grinding, sieving, and storage.
0.734 0.042 0.172
...
0.686 0.110 0.069 0.081 0.021
0,004 0.003 0.002
0.012 0,002 0.001
0 981
0 982
... -
TABLE 11. COMPOSITION DE VERRES(4)
0.692 0.076 0.158 0,030 0.020
0.717 0.103 0.127 0.025
... -
It is also interesting t o speculate how a glass containing over one per cent of iron oxide could have been sehr weiss. One can commend one feature in Table 11-results are rounded off to tenths. It is apparent that the analyst had a comparatively easy time, for but three determinations were made of each glass, either soude et potasse or d i c e having been obtained by difference. In Table I11 Thonerde refers no doubt to RzOZ, and it is interesting to note that in the complete analyses in columns 1 and 2 the analyst was able to obtain well over 100 per cent, even though the analysis did not include probable constituents such as water, carbon dioxide, chlorine, sulfur trioxide, and oxides of arsenic.
Glass is sold on physical rather than chemical requirements, and the needs for analyses are those connected with control of manufacturing operations, duplication of glasses, and researches. The methods of analysis that are employed are not oery different f r o m those used in early days, although the developments of new types of glasses and the adoption of revolutionary methods of manufacture have necessitated certain changes. The glass analyst is not subjected to the crosschecking that is the lot of the analysts who are engaged in the analysis of metallurgical materials. More exacting demands will no doubt be made in the future, not only with regard to speed, completeness, and accuracy of analyses, but also to determinations of constituents that occur in exceedingly small amounts and to the states in which some of the constituents occur.
...
...
0,005
... ... ~-
0.010
In Table I the decimal method of expressing results has one advantage, a t least-in starting from the decimal point, the analyst mas ashamed to attach more than three figures.
854
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 25, No. 8
TABLE IV. FIRSTANALYSESOF SODA-LIME GLASS ( I n per cent) Si02
General av. Av. deviations from general av. Results outside av. deviations Av. of results within av. deviations Most probable value.
NazO
CaO
73.46 73.68 73.71 73.77 73.79 73.94 73.97 74.00 74.07 7 4 . 0Q4 74.09 74.21 74.52 75.39
13.25 15.28 15.97 16.63O 16.81 16.84 16.84 17.00 17.02 17.10 17.13 17.27 17.33 17.83
4.49 4.53 4.65" 4.65 4.71 4.71 4.73 4.75 4.76 4.77 4.83 4.84 4.92 5.09
hlg0 3.04 3.06 3.07 3.23n 3.26 3.35 3.35 3.36 3.36 3.37 3.39 3.39 3.48 3.50
0.078 0.223 0.24 0.26 0.28 0.285 0.32a .O.35 0.35 0.38 0.44 0.60 0.63
...
0.069 0.07 0.07 0.08 0.10
74.05 0.30 5 73.99
16.59 0.76 3 16.90
4.74 0.11 4 4.74
3.30 0.12 5 3.34
0.34 0.11 4 0.43
0.065 0.01 4 0.065
The extent of these changes can be illustrated by experience here with the Bureau of Standards standard sample of sodalime glass. This glass showed, as was expected, no loss on ignition when a solid piece was dried a t 110" and then ignited a t approximately 1000" C. A second piece showed a loss of 0.16 per cent upon ignition after it had been ground to a fine powder in an agate mortar and dried a t 110' C. After storage for several months, similar treatments revealed that the loss on ignition had climbed to 0.83 per cent. In terms of silica, the analyst would have reported 74.0 per cent on the solid piece, 73.9 on the recently ground sample, and 73.4 on the stored sample. Such changes are, of course, caused by the fixation of water and carbon dioxide, and are to be expected in fired ceramic products. So far as analyses are concerned, they are of moment because (1) results obtained in analyses of powdered glass, do not truly represent the composition of the glass in the tank or in the uncrushed state, (2) they cause discrepancies in results reported by different analysts, and (3) they cause such changes in standard samples during storage that all results must be calculated to a loss-on-ignition rather than a dried-at-100" C. basis.
METHODSOF ANALYSIS As already stated, methods for the determination of the principal constituents of glass have not changed radically in the last hundred years. Determinations are still being made by (1) fusing with sodium carbonate, (2) evaporating the acidified melt for silica, (3) precipitating with ammonium hydroxide for iron and alumina, (4) precipitating with ammonium oxalate for calcium, and finally ( 5 ) precipitating with ammonium phosphate for magnesium. Occasionally, as in olden times, silica is determined by difference, after the remaining constituents haTe been determined in a solution obtained by volatilizing the silica with hydrofluoric and sulfuric acids. Alkalies are still gathered as the chlorides, and sodium is reported by difference after potassium has been precipitated and weighed as the chloroplatinate. Certain modifications of the old methods which have been developed, and a few new procedures which are beginning to be used to some extent, deserve special mention. Taking them in order they are: (1) Improvements have been made in methods of breaking up the sample, such as adding a minimum amount of sodium carbonate and fluxing a t its softening point (875' C.) ( 2 ) thereby insuring better decomposition and a t the same time introducing less alkali salt. Ammonium chloride has been added t o the old calcium carbonate flux, thus aiding the extraction of the alkalies. The production of a pure and reasonably priced perchloric acid has given us another high-boiling acid to use in conjunction with hydrofluoric in decomposing samples of glass which are to be used in
i11203
LO66 01
Fez03
K?O
0.03 0.05 0.057 0.06 0.062 Q.064" 0.064 0,068
0.03 0.040 0.04 0.05 0.05 0.06 0 13 0 60 4.10
0.068
SOa
IGNITIOI
0.42 0.10 3 0.43
0.27 0.05 5 0.26
..
.. .. 0.57 0.79 1 0.13
determinations of the sulfate ion, or which contain constituents, such as lead, which form insoluble salts with other acids. (2) In determinations of silica, double evaporations are required for reasonably accurate determinations of silica; even so, some escapes and must, in the most accurate work, be recovered by special treatment of the precipitate obtained with ammonium hydroxide. Double treatments are desirable in practically all of the old determinations. The advent of perchloric acid has also given another medium in which silicic acid can be dehydrated. The common use of boric oxide has necessitated changes in umpire determinations of both silica and alumina. (3) The determination of alumina remains essentially as it always has been; it is usually determined by difference because there is no selective method for its determination. The advent of 8-hydroxyquinoline has opened up possibilities which will be discussed later. (4) Methods of determination for iron have changed radically in execution but not in principle. The substitution of potentiometric titrations for the older processes is an advance that has yielded the increased accuracy that has been demanded in determinations of this element, and a t the same time has eliminated troublesome operations such as the destruction of stannous chloride by mercuric chloride. ( 5 ) Calcium is still determined by the oxalate method, although we have learned that it is not necessary first to separate iron and aluminum if we are not interested in these elements, or if we wish to shorten the time required for the complete analysis of a glass. I n other words, the oxalate may be precipitated a t a pH of 4 to 5 instead of in alkaline solution as of yore. (6) Many still determine magnesium by the ancient phosphate method. This is far from perfect, with such drawbacks as the need for prior removal of most of the other elements, the slowness of precipitation, and the difficulty of ignition. As for improvements in the method, r e have learned that the volatile reagent diammonium phosphate is superior t o fixed reagents such as disodium phosphate, that the phosphate must be reprecipitated if accurate results are to be obtained, and that it is not necessary to remove elements such as iron and aluminum if they are bound in complex ions by the use of reagents such as citrates or tartrates. By far the most important advance in the determination of magnesium is the discovery of the %hydroxyquinoline method. ( 7 ) Of the ordinary elements in glass, we have still to consider the alkalies. As already stated, the use of the calcium carbonate-ammonium chloride flux has simplified the breaking up of glass and the extraction of the alkalies. From this point, many still determine potassium by the chloroplatinate method and sodium by difference, as was
August, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
done more than a hundred years ago. We now have, however, some desirable new methods a t our disposal. The handy reagent, perchloric acid, which has already been mentioned in connection with the decomposition of glass and the determination of silica, serves still another useful purpose-determinations of potassium, in which the element is precipitated as the insoluble perchlorate instead of the chloroplatinate. As for sodium, we have in the triple acetate reagent a long desired precipitation method for its direct determination. Unfortunately the method has the drawback that the precipitate is so voluminous that only small amounts of sodium can be handled. (8) Space will not permit a discussion of methods for the determination of the less commonly considered components (such as compounds of sulfur, chlorine, arsenic, titanium, and zirconium) of soda-lime-silica glasses, the special components of glasses such as borosilicate, flint, or crown, or the small amounts of added coloring or color-correcting compounds. It is, however, desirable to call attention to 8-hydroxyquinoline. It would seem a t first glance that this reagent would find but limited application in analysis, for it reacts with a large number of elements in feebly acid or alkaline solutions. Although it is not a very selective reagent, it does possess some very desirable characteristics. Its general precipitating power and the fact that it is a volatile reagent find good use in removing the ordinary elements from solutions in which determinations of alkalies are to be made. For example, recent work a t the Bureau of Standards indicates that one can obtain the alkalies as the sulfates by (1) volatilizing silica by the customary treatment with hydrofluoric and sulfuric acids, (2) adding, in succession, ammonium hydroxide, ammonium oxalate, and 8-hydroxyquinoline, (3) filtering, and (4) evaporating the filtrate and igniting to expel ammonium salts and organic matter. A second useful application follows because S-hydroxyquinoline precipitates magnesium quantitatively in the filtrate that is left after separating calcium as the oxalate, and the precipitate can be dried and weighed, or dissolved in acid and titrated, thus affording a much needed titration method for magnesium. It has been found a t the Bureau of Standards that calcium oxalate does not react with 8hydroxyquinoline, and that oxalic acid does not interfere in titrations of it. It is therefore unnecessary to go through the extra step of filtration and washing of calcium oxalate if determinations of magnesium albne are desired or rapid determinations are needed.
855
filtrate by reducing the acidity so that from 3 to 5 ml. of 10 per cent acetic acid is present. The zinc in turn can be separated from aluminum by dissolving the precipitate in dilute hydrochloric acid and reprecipitating in a solution containing 3 grams of sodium tartrate and 15 ml. of a 10 per cent solution of sodium hydroxide per 100 ml., after which the aluminum can be reprecipitated by rendering the sodium hydroxide filtrate acid with acetic acid. Finally, the filtrate obtained in the precipitation of aluminum and zinc can be rendered faintly acid and treated with ammonium oxalate to obtain calcium, after which the new filtrate can be rendered alkaline to precipitate the magnesium as minolate. - I
ACCURACY OF RESULTS OBTAIKED As for the accuracy of the results that are obtained in present day methods of analysis, it should be remembered that every result that is reported for a constituent of a glass is a matter of opinion rather than fact, and that therefore the true result can never be known. How difficult it may be to choose even a most probable value can be illustrated by the data shown in Tables IV and V. Here the analysts were trying to do good work and were no doubt making good enough analyses for the control of manufacturing operations; in such work it may not matter whether results are in error, so long as the error is constant. In other words, a precise method may be as good for the purpose as an accurate one. A contributing factor to any present inaccuracies in analyses of glass is the fact that the glass analyst is not subjected to the constant checking by consumers that is the lot of analysts of materials that are sold under chemical requirements. Glass analysts, like other analysts, are careless in reporting results, and thereby cause false impressions as to their powers. They should therefore determine the limitations of the methods of analysis which they use, and round off the results of analyses to a figure for which they are willing to vouch. For example, in the analysis of glass, analysts do well to obtain results for silica that are accurate to 0.1 per cent. So why report to the second or third decimal place? If the glass technologist needs such accuracy, this must be achieved by changing methods of analysis and not by tacking on figures.
FUTURE TRENDS OF CHEMICAL ANALYSISOF GLASS As for analyses of glass in the future, it is probable that there will be a demand for greater completeness, including the elements that may be present in extremely small amounts.
TABLEv.
FIRST
Si02 64.74 65.1 65.16 65.36" 65.37 65.41 66.26
...
PbO 16.79 17.00 17.1 17.24 17.30 17.38 1 7 . 50a 17.51
8.05 8.19 8.38" 8.40 8.41 8.61 8.73
5.62 5.64 5.68 5.73a 5.78 6.07 7.20
1.39 1.4 1.40 1.41" 1.42 1.49 1.52 1.55
0.04 0.15 0,201 0.22" 0.22 0.24 0.243 0.29
0.014 0.03 0.07 0.20~ 0.21 0.21 0.23 0.4
0.12 0.156 0.178 0.18 0.181a 0.235 0.297 0.3
0.02 0.029" 0.032 0.04 0.05 0.053 0.06 0.09
0.04 0.044 0.047 0,0485 0,049 0.051 0.057 0.067
65.34 65.28 2
17.23 17.25 4
8.39 8.40 4
5.96 5.75
1.45 1.42 3
0.20 0.21
0.17 0.19 3
0.21 0.19 3
0.047 0.047 3
0.05 0,048 3
ANALYSESOF LE.4D-BARIUM GLASS (In per cent)
General av. Av. of results within av. deviations Results outside av. deviations a M o s t probable value.
Kz0
..
The different uses to which the reagent can be put are also illustrated by the following outline of interesting separations that have been described by Granger ( 3 ) . I n this series of treatments, iron is first precipitated and separated from aluminum and elements such as zinc by treating with 8-hydroxyquinoline in 100 ml. of solution containing 25 per cent of acetic acid and 4 grams of sodium acetate, and filtering. Aluminum and zinc can then be precipitated in the
..
1
2
There will also undoubtedly be a demand for determinations of the states in which some of the constituents occur-for example, the relative proportions of the oxides of iron, manganese, arsenic, or just what compounds of selenium are present in ruby glass. I n some of this work we shall probably have to make a greater use of physical aids such as spectroscopic and x-ray methods. We shall also have again to modify the methods of analysis
856
I N D U S T R I ,4L A N D E N G I N E E R I N G C H E M I S T R Y
or devise more selective methods to take care of new combinations such as were needed when glasses containing fluorine and boron became common. I n line with needs for cutting down the time required for determinations, there will be a gradual substitution of unit methods of analysis for the old continuing methods. In other words, instead of determining silica, alumina, iron oxide, lime, and magnesia on the one sample with its attendant delays, we will come more and more to the taking of separate samples for each determination, or of dividing solutions and carrying determinations through simultaneously. Thus, we will determine silica in one sample, sodium and potassium, or either one singly in another sample, iron in a third, and a t the same time carry along other samples in which silica is volatilized a t the start, and the solutions used for lime alone or for iron and aluminum. In the last case the filtrate which is obtained may well be divided for simultaneous determinations of lime and magnesia, or the whole solution used for either one alone. Separate samples will also, of course, be used for minor as well as special constituents.
Vol. 25, No. 8
Finally, there will probably be needed more complete examinations of raw materials, for oftentimes these contain unsuspected impurities, as, for example, an eastern limestone which was the mysterious source of a constant small cobalt content of a certain glass. It is interesting to note what can be found in ceramic materials if a diligent search is made. For example, the Bureau of Standards’ standard samples of flint and plastic clays are perfectly normal products so far as we know, and yet they contain constituents such as titanium, zirconium, phosphorus, vanadium, chromium, manganese, copper, barium, and molybdenum. LITERATURE CITED (1) Berthier, P., Dinglers polytech. J., 39, 43 (1831); Ann. chim. phys., 1830,443. (2) Finn, A. N., and Klekotka, J. F., Bur. Standards J. Research, 4, 809 (1930). (3) Granger, A., Ceramique verrerie, No. 837, 137 (1932). (4) Peligot, E., Compt. rend., 83, 1132 (1876). ( 5 ) Weber, R., Ann. Physik, 242, 443 (1879).
RECEIVED April 10, 1933.
Refractories for the Manufacture of Glass FREDS. THOMPSOK AND HOBART M. KRANER,Corhart Refractories Company, Louisville, Ky.
R
EFRACTORIES m u s t The development of glassmaking is briefly c h a m b e r , heating t h e bottom traced, pointing out the status of the refractories and back of the Pots, and the not Only be resistant to the corrosive action of used and the part they played in this deuelopopenings g l a s s was in the w o front r k e d walls. out of the the glass batch, but they must merit* The chemical aspects Of the manufacture Agricola says regarding the be p h y s i c a l l y and chemically correct to prevent contamination of refractories and the chemical considerations refractories used: “These bricks in the use of these refractories are discussed. are made of a kind of clay that of the glass. Katurally, refractories have developed with the iuodern refractories and their application cannot easily be melted by fire or art of glass manufacture. The resolve into powder. This clay to th,e glass industry include discussion of: first furnaces (around 2000 B. c.) is cleaned of small stones and were of the puddling type. As flux flux Of crysta11ine beaten with rods. The bricks early as 1000 BIC. built-up furminerals, bonded with clay or other binders; are laid with the same kind of naces were in use. I n the height f l u x block manufacture by the electric foundry clays instead of lime. From the method; superstructure refractories f o r use same clay, the potters also make of the Roman Empire, colored and t r a n s p a r e n t glasses, intheir vessels in pots which they aboue glass contact line, including silica, fire cluding window glass, were aldry in the shade.,, ready being made, and covered clay, cyanite, I n d i a n sillimanite, electric Agricola further describes a pots were reported to have been refractories, andalusite, high-aluminous, and practice that is familar to us in use. others. (namely, that of preparing a pot The greatest a d v a n c eme n t for the furnace i n s t a l l a t i o n ) : from t h e n o n seems to have “Pots are first warmed by a slow taken place early in the sixteenth century when lead flint fire in the first urnace so that the vapors may evaporate and glass was discovered, giving the glass industry great impetus. then by a fiercer fire so that they become red in drying. iifterThe use of coal and what appears to be a rediscovery of the ward the glassmakers open the mouth of the furnace, and, seizvalue of covered pots were notable milestones in glass de- ing the pot with tongs, if they have not cracked and fallen to velopment. This seems to have been a necessity owing to pieces, quickly place them in the second furnace, and they fill them up with fragments of the heated vitreous mass or the reduction of lead. At this time the furnaces appear to have been made largely with glass.” I n 1699 Blancourt (3) related: “The material which serves of sandstone, known as firestone, and only the pots were made of clay. Agricola ( 1 ) in 1550 described the process of for building these furnaces are brick for the external parts and glassmaking in an interesting manner. The furnace was for the inner parts, a sort of ‘Fuller’s Earth’ which is gotten round and dome-shaped, and three levels of chambers high. frcm Belii.re near Forges and which is the only earth in The lowest chambers were for fuel, the next above held the France which has the property of not melting in this excessive pots, and in the upper level ware was often annealed, al- heat; and it is of this same earth that the pots are also made though frequently an entire separate furnace was provided which will hold the melted metal for a long time.” for annealing. Usually still another furnace for the preparaFor the next hundred years, furnace designs changed tion of cullet was used. Sometimes the cullet furnace was little. Sandstone bricks and blocks continued to be used supplanted by a calcar arch which was really an auxiliary for the construction of furnaces and the furnace shape seems fritting furnace attached to the main furnace. The flames to have gradually changed from round to oval and then to of the furnace described by Bgricola passed up into the pot rectangular. During this period factories were being erected a
