Vol. 42, No. 3
INDUSTRIAL AND ENGINEERING CHEMISTRY Boller, E. R., U. 9. Patent 2,097,509 (Nov. 2, 1937). Campbell, K. S., and Sands, J. E., Ibid., 2,462,803 (Feb. 22, 1949). Carroll, S. J., Ibid., 1,631,468(June 7, 1927). Cuppery, M . E., I b i d . , 2,212,152 (Aug. 20, 1940). Daly, A. J., Ibid., 1,941,664 (Jan. 2, 1934). Dreyfnss, C., Ibid., 1,907,521(May 9, 1933). Eichengrun, A., I b i d . , 1,985,771 (Dec. 25, 1934). Fischer, E. K., Ibid., 2,461,538 (Feb. 15, 1949). Ford, F. M., and Hall, W.P., Ibid., 2,482,755, 2,482,756 (Scpt. 27, 1949). Gay-Lussac, J. L., Ann. (,him. phys., 18, 211 (1821). Gulledge, H. C., and Seidel, G . R . , Isn. ESG. C m k f . , 42, 440 (1950). Hopkinson, H., U. S.Patent 2,250,483 (July 29, 1941) ; 2,343,186 (Feb. 29,1944). Jones, G., Juda, W., and 6011, S., Ibid., 2,452,054, 2,452,055 (Oct. 26,1948). Leatherman, E. W., I b i d . , 2,463,983 (March 8,1949). Lindsav. W. G., Ibid., 1,133,385 (March 30, 1915). Little, k. W., “Flameproofing Textile Fabrics,” A.C.S. Monograph 104, New York, Reinhold Publishing Corp., 1947. McLean, A., and Marrian. S.F., U. S. Patent 2,470,042 (May 10,1949).
(19) Perkin, W. H., Ibid., 844,042 (Feb. 12, 1907). (20) Pollak, F. F., Ibid., 2,418,525 (April 8 , 1947). (21) I b i d . , 2,421,218 (May 27,1947). (22) Pollnk, F. F., and Fassel, J., Ibid., 2,464,342 (March 15, 1940). (23) Ramsbottom, J. E., and Snoad, A. W., “Fireproofing of Fabrics,” Fabrics Co-ordinating Research Comni., Dept. Sci. and Ind. Research (Gr. Brit.), First Report, 1925; Second Report, 1930; Third Report, 1947. (24) Rosser, C. -M., U. S.Patent 2,305,035 (Der. 15, 1942). (25) Ruhrchemie A,-G., Brit. Patent 486,766 (June 7, 1938). (26) Triggs, W., I b i d . , 476,043 (Oct. 31, 1936). (27) Truhlar, J., and Pantsios, A., U. S.Patent 2,461,302 (Feb. 8, 1949). (28) Van Tuyle, R., Am. Dl/estu$Reptr., 32,297 (July 5, 1943), (29) White, C. B., U. S. Patent 2,427,997 (Sept. 23, 1947). (30) Whitehead, W., I b i d . , 2,032,605 (March 3, 1936). (31) Woodruff, J. A , , Ibid., 2,454,245 (Nov. 16, 1948). (32) York Research Corp. of Conn., Stamford, Conn., Reports I and 11, “Textile Flameproofing Compounds,” distrihuted by Am. Hotel hssoc., 221 West 57th St., New York, X . Y. (33) Zelger, G. E., U. S. Patent 1,586,775(Nov. 8, 1932). RECEIVED September 26, 1949. N.R.C. Project Q.M.C. 28, Dermrtment of Chemical
Engineering, Columbia University, Kew York, N. Y.
DURABLY FLAME-RETARDING CELLULOSIC M A T E R I A L S HUGH C. GULLEDGE AND GEORGE R. SEIDEL Pigments Department, E. I. du Pont de Nemours & Company, Inc., Wilmington, Del. This paper describes a new method for durably flameretarding cellulosic materials such as cotton and viscose. The chemical employed is based on an aqueous titaniumantimony complex known as Erifon flame retardant which, after a two-step process, appears to combine chemically with the cellulose molecule. Methods and problems of
application and propertirs of a variety of treated fabrics are discussed, and limitations as to durability, dyeing, and fields of application are pointed out. Technical aid is necessary before an individual mill can satisfactorily apply this process; several mills are now equipped to operate on a commercial scale.
OST papers dealing with the chemistry of titanium begin by pointing out that this element is the ninth most abundant in the earth’s crust, exceeded by oxygen, silicon, iron, calcium, sodium, potassium, and magnesium and trailed b y such familiar elements as sulfur, phosphorus, copper, zinc, and lead. In spite of its abundance, most of the world’s industrial processing of titanium compounds is carried out in the United States and in 1946 amounted to only 125,000 tons per year in terms of titanium content. Table I compares the abundance and consumption of titanium xith more common though less abundant elements. Practically all the titanium has been produced in the form of pigment titanium dioxide, although recently the production of metallic titanium has been started on a limited commercial scale. Although titanium is abundant and relatively cheap and certain fundamentals of titanium chemistry have been known for years, this branch of chemistry is unfamiliar to the average chemist and relatively unexplored by the fen- chemists specializing in this field. It has been recognized for many years that organic compounds containing hydroxyl groups !\-ill react with titanium compounds. Thornton states ( 4 ) :
be, is closely connected with the hydroxyl group, since it is exhibited by glycolic and not by aretic acid.
It has long been known that certain metallic elements, which normally form insoluble hydroxides, carbonates, phosphates, etc., with appropriate reagents, fail to do so when certain organic substances-e.g., citric acid, tartaric acid, dextrin, sucrose, glucose, lactose, etc.-are present in sufficient quantity.. , . Confining our attention then to the organic acids, we may generalize by saying that this property, whatever its mechanism may
It has now been firmly established that titanium forms stable and definite compounds with many organic molecules containing hydroxyl groups. But most titanium compounds readily hydrolyze and form a precipitate of titanium hydroxide according t o the reaction: Ti(0R)I
+ 41120 +Ti(OH), + 4ROH STRUCTURE
Besides its four primary valences, titanium also has two sccondary valences, which add up to a coordination number of six This permits ring formation 01’ a chelated structure. Whero chelates can be formed with titanium, the resulting conipounds
Abundance and Consumption of Common Elements Abundance in Tons Consumed Element Earth’s Crust, ( 1 ) in 1946 (6) Ti 0 63 125,000
Table I.
P
0.13
Mn
0.10 0.052
S
CI CU
Zn Ph
0.048 0.010 O.OO{ 0.002
1,130,000 829,000 4,094,000 1,166,000 1,135,000 988,000 950,000
441
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1950
are water-stable-for example, in the case of glycolic acid (hydroxyacetic acid) such a chelated structure with titanium is probable and titanium glycolate is water-stable. On the other hand, acetic acid cannot form a chelate with titanium and therefore titanium acetate is readily hydrolyzed. The chelated structure for titanium glycolate may be pictured as follows:
CI
O ‘H
No such ring structure can he written for titanium acetate.
The authors have studied this chemistry for a number of years, striving t o understand it better and, if possible, find a practical application for its use. Because cellulose contains three hydroxyl groups for each glucose unit, reaction between titanium and cellulose should occur. Actually it was found that titanyl sulfate (TiOS04) reacts with gel cellophane in the proportion of approximately i mole of titanium per glucose unit. The resulting film is translucent and brittle, but can be plasticized with glycerol. The combination of titanium with the glucoside unit may be:
Titanated cotton and viscose are durable t o dry cleaning - and laundering. Titanated cotton and viscose have fair mildew-resistant properties. It is known that the esterification of cotton improves mildew resistance. Titanium shows no evidence of combining chemically with fabrics that have no free hydroxyl groups. Because titanyl salts will readily hydrolyze, excess acid is necessary to maintain aqueous stability. Concentrated solutions of titanyl salts require less free acid than dilute solutions. For most practical concentrations, the pH approaches zero. The greater the titanyl ion concentration, the better the swelling. The anion is also of importance. Much of the authors’ early work was confined to the sulfate of titanium, because it is readily available and easy to handle. A comparison of common organic and inorganic acids showed that titanyl chloride was the best swelling agent and combined most readily with cellulose. This raises the question of acid degradation of cellulose. Of course, this is a time-temperature relationship and, a t elevated temperatures, tendering will occcur in a matter of seconds. At room temperature, however, no tendering occurs in 15 minutes, and with heavier fabrics protected against evaporation (which otherwise would result in local overconcentration) no tendering is noted after an hour. Theoretically, a chemical reaction between titanium and cellulose should proceed almost instantaneously, and perhaps does. In practice, however, some time must be allowed for penetration, and the heavier the fabric and tighter the weave, the more time is required. With plush, where the pile is loose and each thread is separate from its neighbor, little or no time lag is required. Heavy, densely woven flat goods may require 15 minutes. That penetration and not reaction rate is the governing factor is indicated by the fact that certain wetting agents are very effective and thorough scouring of a fabric reduces the necessary time lag. Once it had been decided that titanium reacts with cellulose or a t least is held by strong secondary bonds, the next step was to find a practical application. It had been early noted that titanated cotton burned less readily than untreated fabric, but the degree of flame retardancy was far from practical. Other workers have noted that tin oxide will inhibit flaming, and the use of antimony oxide with chlorinated paraffin is well known. To this list of inorganic compounds may be added tungsten, aluminum, zinc, iron, etc. Their observed effectiveness was reported in 1947 by Ramsbottom ($), who shewed that deposition of insoluble inorganic compounds precipitated within a fabric by a two-step process is relatively ineffective as compared to watersoluble salts such as ammonium phosphate and zinc chloride.
“---
Table 11.
Minimum Quantities Required t o Prevent Flame Propagation Water Soluble, % Ammonium phosphate Zino chloride
The dotted lines indicate where coordinate bonds may attach, although this is entirely postulated. In the case of the abovementioned titanated cellophane, there may be colloidal deposition so small that i t cannot be detected. Electron microscopy, electron diffraction, and x-rays fail to detect titanium, even though it is present in large amount. On the other hand, coordinate bonding would be expected only slightly to modify the crystalline structure of cellulose. Several lines of indirect evidence indicate that bonding does occur between cellulose and titanium: Titanium can be added to gel cellophane, corresponding to 1 mole of titanium per glucose molecule. Titanium compounds will not react with cellulose acetate; the ester has satisfied available hydroxyl groups. Titanium compounds insolubilize polyvinyl alcohol.
Water Insoluble, % Ferric oxide
12 12 19
St,niinic oxide
20 ~.
Lead monoxide Manganese dioxide Ferric chromate Antimony oxychloride Lead chromate Zinc stannate Tin tungstate Aluminum stannate Antimonous oxide
21 22 24 30 37
~~
40
50 54
79
Ramsbottom has reported numerous other inorganic substances which were considered flame retardants, but now states that in previous tests, which showed some of the substances to be good fireproofers, the fabrics after impregnation were probably not thoroughly washed t o remove soluble salts.
INDUSTRIAL AND ENGINEERING CHEMISTRY
442
The combination of titanium with other metal salts was the next step. Some combinations showed a degree of flanieretardancy surpassing that of titanium alone. Of the many tried, however, antimony trichloride with titanyl chloride proved to be the most effective-an altogether unexpected but promising result-and this combination has been developed and is sold under the trademark Erifon flame retardant. Antimony oxide alone is ineffective; it is a t the bottom of Ramsbottom's list. Yet the impregnation of cotton or rayon with titanyl chloride plus antimony trichloride follomd by neutralization with an alkali-such BS 15% sodium carbonate-results in a durably flameretarded fabric. Such treated fabrics are still flame retardant after 100 household launderings. With such strong affinity, we assume some such structure as: \
\
,
~
H
~
'\,
O 51- ,OH -0-Sb.
/'
'OH
/OH
'OH
v--/
Ho
At ignition temperatures, gascs arc released which smother the flame. This is true, at least in part', of halides and animonium compounds. Flame-retardant cheiiiicals melt a t ignition temperatures and coat the fiber with 'a nonflammable protective coating. Conipounds of boron may retard finminability of textiles by suck behavior. The mechanism ( 2 ) which seems best to explain the action of titanium and antimony is that this combination alters the product,s of pyrolysis, resulting in more charred residue and less volatile tars. As a matter of fact, t'his theor may best explain the action of most flame-retardant agents. as noted above, coordinate bonding or other chemical linkages stabilize cellulose a t ignition temperatures so that larger fragments are held together, this should result in a carbon skeleton which is less flammable than smaller, volatile organic fragments would be. This explanation of the effectiveness of titanium and antimony as a flame retardant for cellulosc is by no means clear-cut. 13y this theory, titanium should he an excellent flame-retardant agent, because it is this element which reacts with the cellulosc molecule. Actually, titanium alone is not as effective as :L combination of titanium and antimony, which imparts a practical degree of flame retardancv, not destroyed by laundering and dry cleaning. On the oth& hand, chemicals which are effective fiame retardants, and for which no chemical linkage with cellulose is ordinarily assumed, equally increase the char and decrease the tar of treated cotton. This is demonstrated by the data in Table 111, which compares thc products liberated by burning cotton treated with the agents listed. Other treating agent,: were tested, but theseedata are sufficient to illustrate tho effect of typical flame retardants.
E,
__
~
~~
Table 111.
Again, this assumption has not been proved or disproved, but current studias are under way in an attempt to establish the validity of such a structure. FLAME-RETARDANT ACTION
A few words about the theory of flame-retardant action. Several mechanism have been proposed to explain the effectivcness of chemicals that retard the flammability of combustible fabrics. Of the theories listed beloPi, it is probable that a ronibination of effects is involved in any particular flame-retardant treatment. The first t n o have been advanced but not too seriously advocated.
The heat conductivity of the fabric is increased by the treating agent, so t h a t heat is rapidly carried away to such an extent that the flaming temperature cannot be maintained. The treating agent is endothermic near combustion temperatures and thus reduces the temperature of the fabric below the point where flaming proceeds.
Figure 1.
Vol. 42, No. 3
("4)zHl'Oa
Effect of Typical Flame Retardants
(Id%)
Borax-boric acid (13%)
TfLniI> C 5 50 3 50 ROO
a50
1120
%
("ioL
Char
%
%
30 45
22 7 5 1
39 47
I,
40
'1 8
Tar,
41
Ti/Sb (10%)
500 350
i7 37 49
Control
,500 350
12
s
12 5
54 42
33 35 37 29 33
1
ii
7
0
c,
The technique used for obtaining these results is bricily described because it differs fi.om the method employed by some others. A portion of a vertical borosilicate glass tube is heated to the indicated temperature by a surrounding furnace, and nitrogen gas is swept through continuously from top to bottom. When all is in readiness, the sample is dropped from the cool upper portion of the tube into the hot. area. KOoxygen is present, and the nitrogen sweeps the products of pyrolysis through glass wool which t,raps the tars. Water is collected in a desiccator tube arid carbon dioxide in a lime tower. The charred residue is weighed
Standard Textile Equipment
March 1950
INDUSTRIAL AND ENGINEERING CHEMISTRY
443
For the most p u t , flame-retardant agents, effective in amounts of less than 20 to 25%, have been halides and soluble salts of ammonia, phosphorus, and boron. Of these four, only phosphates are readily insolubilized, but insoluble inorganic phosphates are ineffective flame retardants-calcium phosphate, for example, is not effective. Attempts have been made to coat these soluble salts with resins or polymers or to include in the coating composition halides such as chlorinated paraffin. The complex of titanium and antimony is one of the few examples of an insoluble inorganic treatment which confers practical and lasting flame retardancy upon cotton and rayon. FLAMMABILITY AND AFTERGLOW
Flammability is a term usually reserved for the actual flaming of a fabric; many chemicals are effective in preventing this kind of combustion, particularly after the source of ignition has been removed. Actually, in most cases, treated fabrics tested in the vertical position will suffer a conical-shaped burned spot at the point of contact with the igniting flame and flaming will spread no further. However, many flame-retardant chemicals actually promote the flameless, incandescent combustion of fabrics, known as afterglow-for example, ferric oxide and stannic oxide will promote afterglow, even though they are among the better flame retardants. Untreated cotton fabrics also have a tendency to afterglow after the igniting flame has been removed. In many cases, afterglow is restricted to the above-mentioned charred area-the conical-shaped spot burned by the igniting flame. In many tests, this is considered satisfactory and some specifications do not even mention the time of afterglow, if it is confined to the initial charred area. In such ernes, the total length of burned cloth consumed by both flaming and afterglow is usually specified and must be less than a certain number of inches. The lighter the fabric, the longer the burn may be. Other specifications require that the afterglow be less than a specified number of seconds. The actual requirement may be dictated by the psychological effect upon the consumer, who expects a treated fabric not to burn by any mechanism, fast or slow. For some uses afterglow is unimportant and can be ignored, although its absence is probably desirable-other things being equal. Generally speaking, however, it is relatively easy to flame-retard heavy fabrics and difficult to prevent afterglow. Light fabrics are more difficult to treat for flame retardancy, but oftentimes require no additional chemical to control afterglow. The analogy seems to be that it is easier to flameproof a log than excelsior; no analogy is offered for afterglow. .4ctually, the theory of afterglow is none too satisfactory. Heavy fabrics seem t o generate and hold so much heat during afterglow that the adjacent area is charred and thus likely to continue the afterglow. Undoubtedly, many oxides, such as ferric and stannic, act as catalysts to promote this incandescent combustion. The authors have found that afterglow of titanium-antimony treated fabrics can be controlled by the use of silica padded onto the fabric as sodium silicate and precipitated by the application of the acidic titanyl chloride-antimony chloride complex. The actual application of the flame-retardant chemical Erifon requires standard textile equipment ~ t 9shown in Figure 1. Because this flame retardant contains several per cent of exems hydrochloric acid, the padder pan should be rubber lined; the padder rolls should also be rubber covered and all bearings protected against s lashing. The J box can be of wood or rubbercovered steel; ifother means of lag ing the fabric are used, such as skying rolls, these, too, shouird be rubber covered. All operations are carried out a t room temperature, The padder should give the best impregnation and expression possible. This usually means hydraulic pressure, for it is important to drive the solution into the center of tightly twisted yarns and closely woven fabrics. For reasons of economy, it is also important to obtain as low a wet pickup &R possible. Certain
Figure 2.
Flame Resistance of Treated Fabrics
Both fabrics are 6-ounce herringbone twill. The igniting flame was applied a t the 30-second mark and in 8 seconds the untreated fabric Zeft) began to flame. After 19 seconds t h e flaming of untreated abric was severe. In 28 seconds t h e treated piece was intact except for a charred spot; the untreated fabric was in full flame.
i
INDUSTRIAL AND ENGINEERING CHEMISTRY
444
Table IV. Effect of Outdoor Exposure at Miami, Fla. (Nov. 19, 1947,t o Sept. 5 , 1948. Fabric, 12.29-ounce duck) After Char Warp Flame, Length, Treatment Exposure Break Sec. Inches Erifon Zelen. None 181 0.2 2.6 Vat O.D. No. 7 .. 0.2 2.9 Stored 291 days 124,694 grain cal. per sei. cm. 1291 d a m ) 152 0.2 3.4
+
’ -
--.-
29
..
agents compatible with Erifon may aid in the impregnation of difficultly wetting fabrics. The J box probably allows for diffusion of the titanyl chlorideantimony chloride complex into the fabric. In the case of plush, where the pile is raised and every thread is more or less free of its neighbor, very little lag is necessary; a minute is enough. With heavier tightly woven fabrics, 15 minutes are required to reach equi1ibr)ium. The authors have found no cases requiring more than 15 minutes, although longer times, within reason, cause no deleterious effects. Nevertheless, 15 minutes should be an abDolute maximum lag time, for the sake of safe operating practice. Thorough, uniform, and instantaneous neutralization is of extreme importance. For this reason a small neutralizing tank in front of the main range allows for constant flow of 15% soda ash and frequent turnover of the tank’s contents. There must be no folds in the fabrics, as these will be apparent in the finished fabric. A spray should be considered optional and used only where its value has been demonstrated for a particular fabric. If neutralization is not rapid and complete, the partially neutralized flame retardant will leach in the solution resulting from incomplete neutralization. Some hydrous oxides are formed, and as much as possible of these should be carried away a t this first step, so as not t o result in chalkiness of the finished fabric. The subsequent boxes in the neutralizing range complcte the neutralization, the number of boxes depending upon the particular fabric being processed. To obtain complete neutralization, a sample of cloth removed from the range should be alkaline and remain somewhat above pH 7.0 for about 10 minutes. If, by diffusion, the fabric gradually becomes acidic, longer contact with soda ash in the range is necessary. Figure 1 shows water in the last box. This is not a washing step but merely to reduce the alkaline concentration on the fabric. Where continuous handling is provided, the fabric might well go directly to the washer. If, on the other hand, fewer boxes of soda ash are required than the four pictured, one or more of these might also be flowed with water. The next step, washing, is also important, although it poses no particular problem with fabrics that can be rope washed. In these cases, the treated cloth is fed into a slack rope washer with a nip and washed until all excess precipitate is removed. Soap, a synthetic detergent, or a mixture of these can be used; a little soda ash is sometimes added with the soap. Fabrics that cannot be rope washed are difficult to handle. A certain amount of precipitate remains on the fabric and this persists in the finished fabric, appearing as chalk and adversely affecting the appearance. In extreme cases, the hand is also harshened. There are several possible solutions to this problem and work is now under way to find a practical answer. After scouring, the fabric is handled in the normal fashion. It is desirable to apply vat dyes before Erifon flame retardant. Direct dyes are, in general, applied after the flame-retardant treatment, although with certain direct dyes on certain fabrics, dyeing beforehand may be preferable. Some dyes are seriously affected by Erifon, others only slightly. Dyeing is a separate problem with each new application, but to date this has not been found a stumbling block. PROPERTIES OF TREATED FABRICS
Tensile strength is not reduced initially or on aging, by treatment with this flame retardant. Such a broad statement has some exceptions, but the authors have found very few cases where tensile strength was reduced as much as lo%, balanced by cases where tensile strength was increased by as much as 10%. Generally speaking, hand is not adversely affected. Actually, in the case of pile fabrics, the hand is significantly improved with Erifon flame retardant and the proper finishing agents. A
Vol. 42, No. 3
fuller pile results with better scroop and a more wool-like crunch. There is even some indication of improved crush resistance for pile fabrics. I n the case of flat fabrics, the desired hand is directly proportional to the thoroughness of scour. Softening agents can be used according to normal mill practice. The effect of laundering and dry cleaning on titanyl chlorideantimony chloride treated fabrics is a very complicated matter. For example, after one hundred “normal” household launderings, an 8-ounce herringbone twill would not flame when a match was applied to a strip held in the vertical position (Figure 2). By a normal household laundering is meant 15 minutes a t 140” F., with o.5y0soap or synthetic detergent and three 5-minute rinses a t 140”, 120”, 100” F. The flame retardancy of this same fabric was destroyed by five launderings with o.5Y0 soap, 0.5 ounce of sodium hydroxide per gallon, and m-ater a t 210’ F., followed by six rinses and finally a sour with 0.25% fluoride sour. This is a severe but practical laundering procedure for heavily soiled work clothes. This is one of the niost important arid challenging problems that are being tackled in the laboratory at t,he present t,ime. From a practical viewpoint, full-strengt,h Erifon gives maximum durability and maximum cost. Some fabrics do not need a full-strength solution in order to meet the requirements for their expected use. A happy balance between economy and performance must be struck, and this can be determined only by experimentation and an appraisal of the facts pert,inent to any given situation. Erifon flame retardant, properly applied, is not removed by dry cleaning, although there are conceivable exceptions even to this statement. Again, each case must be checked, for this is a new treatment, and where flammability is concerned every precaution must be t,aken. Treated fabric has been evaluatcd outdoors and in accelerated weathering machines. Results show t’hatthis new treatment does not adversely affect tensile strength on exposure to artificial or actual sunlight. In general, dye fading is poorer with treated fabrics than with the control. This means t’hat dyes least affected by this treatment must be selected; practice has demonstrated that this can be done successfully. Erifon treated fabrics are not toxic and do not cause dermatitis. Precautions must be taken in the mill in handling this flame retardant, because it is an acidic aqueous solution. Gloves and acidproof goggles must be worn. After contact, the skin should be rinsed Tyith copious amounts of water. ACKNOWLEDGMENT
The experimental work here reported is the result of many workers. The authors are part,icularly indebted to their coworkers, E. R. Marshall, W. W7.Riches, and b’. L. Dills. Advice and data were also contributed by P. E. Rouse, J. H. Balthis, F. K. Signaigo of the Chemical Department, and J . R.Raslam. LITERATURE CITED
(1) Clark and Washington, U. S. Geol. Survey, Proftwional Paper 127 (1924).
(2) Little, R. W.,“Flameproofing Textile Fabrics,” AM. CHEaf. Soc. Monograph 194, New York, Reinhold Publishing Corp.,
1947.
(3) Ramsbottom, J. E., “Flameproofing of Textiles,” Dept. Sci. Ind. Research, Great Britain, London, H.M. Stationery Office,
1947. (4) Thornton, TV. H., “Titanium,” AM.CHEM.SOC. Monograph, New York, Chemical Catalog Co., 1927. (5) U. S. Bur. IMines, “Minerals Yearbook,” 1946. RECEIVED September 26, 1949
END OF SYMPOSIUM
