September 15,1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE 11. REPRODUCIBILITY OF METHOD ALLOY
1 1 1
1
1 1
1 1 2 3
4
AVERAGE AVERAGE DETERMI- APPARENT CORRECTED NATIONS CALCIUM ClLCIUM
1 1 1 1
1
1 1
1 8 8 8
% 0.0177 0,0189 0.0174 0.0187 0.0177 0.0177 0.0193 0.0177 0.0271 0.0406 0.0620
% 0.0197 0.0209 0.0194 0.0207 0.0197 0.0197 0.0213 0.0197 0.0291 0.0419
....
AVERAQE DEVIATION FROM MEAN
%
-0.0004 $0.0008 -0.0007 $0.0006 -0.0004 -0.0004 $0.0012 -0.0004 1 0 .0003 10.0004 10.0006
315
We are indebted to J. D. Struthers of this laboratory for performing most of the experimental work reported. LITERATURE CITED (1) Hahn and Weiler, 2. anal. Chem., 70, 1 (1927). (2) Shaw, Whitternore, and Westby, IND.ENQ.Cmix., Anal. Ed., 2,401 (1930). RECEIVED June 13, 1933. Presented before the Division of Physical and Inorganic Chemistry at the 86th meeting of the American Chemical Society, Washington, D. C.,March 26 to 31, 1933.
Silicon Tetrafluoride Volatilization W. D. ARMSTRONG, Laboratory of
Physiological Chemistry, University of Minnesota, Minneapolis, Minn.
H E volatilization of siliA highly simplijied apparatus, without gasand their connecting tubes. An scrubbing devices, for the quantitative evolution all-glass apparatus with only a con tetrafluoride as a trap a t -35" c. b e t w e e n the step in the determinaand collection of silicon tetrafluoride gives good digestion flask and the receiver Of fluorine has reached its results since the apparatus can be thoroughly also to give complete reh i g h e s t state of development dried and possesses no dead spaces* BY tempera- covery of fluorine under various in the t h o r o u g h s t u d i e s o f lure control, the loss of fluorine caused by hyconditions of p r o c e d u r e , A and Jacob (6) Reynolds, ROSS, and Shuey (6). These writers, drolysis of the tetrafluoride is usually prevented w h i t e , frost-like s u b l i m a t e and, should hydrolysis occur, the Juorine-conformed in the top of the trap and together with Adolph (1) and in the bends of the connecting Wagner and Ross (8)' adetaining products can be driven into the receiver tubes when scrubbers were used, quate reviews of the subject. Treadwell and Koch (7), wagner by the application of heat to the delivery tube. in spite of all p r e c a u t i o n s to eliminate water from the appaand Ross, and Casares (4) have reported the quantitative recovery of fluorine. However, ratus. This material may have been the same as the "strange Reynolds, Ross, and Jacob recovered from calcium fluoride deposit" first mentioned by Treadwell and Koch (7) in conan average of only 93.5 per cent of the calculated fluorine. nection with their gasometric method for measuring silicon Furthermore, the results of Shuey with sodium fluoride varied tetrafluoride. They, however, observed it only when working from $9.77 to 100.36 per cent and averaged 95.72 per cent. below atmospheric pressure. It seems likely that this deposit Willard and Winter (Q),using a modification of the Casares was silicic acid and hydrofluosilicic acid produced by the hyprocedure, obtained good recovery with inorganic fluorides drolysis of silicon tetrafluoride by water retained on the glass but found low results on the determination of fluorine added walls or formed in the reaction bulb. The rinsings of the trap and tubes were acid in reaction, and after several deterto feed ash. Previous workers, except Casares and others who have minations a white solid accumulated in the apparatus a t the employed a gasometric technic, have found it necessary to points where the original deposit collected. This substance was insoluble in water scrub the silicon tetrabut dissolved in boiling fluoride before it enalkali apd was therefore tered the receiver, in probably s i l i c i c acid. order to remove subI n an all-glass apparastances, chiefly acids, tus designed to collect which interfered with the analysis of the res i l i c o n tetrafluoride c e i v e r c o n t e n t s for quantitatively f r o m fluorine. Various so d i u m silicofluoride decomposed by heat a types of wash bottles similar deposit was obcontaining sulfuric acid served, and the results or s u l f u r i c acid plus of the titration of the silver sulfate or c h r o m i u m trioxide receiver contents f o r have been used t o hydrofluosilicic a c i d a b s o r b hydrochloric were low. The washings of the connecting acid, sulfur d i o x i d e , tube of the apparatus and oxides of nitrogen. Some o b s e r v a t i o n s D required an additional a m o u n t of standard made by this writer inalkali sufficient to give dicate that these wash a quantitative recovery bottles cause a loss of f l u o r i n e chiefly o n of fluorine f r o m t h e a c c o u n t of the diffid e c o m p o s e d silicoFIGURE1. SILICON TETRAFLUORIDE EVOLUTION APPARATUS fluoride. culty of drying them
T
316
ANALYTICAL EDITION
Vol. 5 , No. 5
nJ
FIGURE 2. ASSEMBLEDAPPARATUS
I n order to overcome these difficulties a highly simplified apparatus for the evolution and collection of silicon tetrafluoride was devised. The layer of water adsorbed on the glass can be removed by playing a flame over the partially assembled apparatus. A procedure was developed which usually prevented the formation of the white deposit and a method was found b y which the fluorine, should the deposit form, can be driven into the receiver. This simplified apparatus required the development of the colorimetric method described in the previous paper (9)for the analysis of the receiver contents, since it allows substances which interfere with other fluorine analytical procedures to enter the receiver.
APPARATUSAND METHOD The construction of the evolution apparatus is illustrated in Figure 1 in which B and C indicate ground glass joints and D is the adapter. In the assembled apparatus (Figure 2) A is a rubber tube carrying compressed air. The air-drying train consists of the Mulligan wash bottle, D, charged with concentrated sulfuric acid; the four 25 X 200 mm. tubes, E , containing calcium chloride; the tube, F , of the same size loosely filled with phosphorus pentoxide and glass beads; and tube G, which contains glass wool. H and M are rubber tubes and L is the receiver made from a 25 X 200 mm. test tube, 0 is a mercury-filled pressure regulating device, and P is a trap, the outlet tube of which is connected to a water pump. The apparatus is supported in such manner that the flask, K , can be shaken. Powdered glass for use as a source of silicon is best prepared by finely pulverizing clean microscope slides. The product should be thoroughly dried and stored in a desiccator. Ordinary concentrated sulfuric acid is satisfactory and its use, instead of acids containing excess sulfur trioxide, reduces the possibility of the formation of the difficultly volatile fluorosulfuric acid and lessens the amount of acid collected in the receiver. The procedure to be used in the evolution and collection of the silicon tetrafluoride follows: Thoroughly dry in an oven that portion of the apparatus shown in Figure 1 and mix in the bowl of the flask the sample and 2 grams of powdered glass. If the sample is larger than a gram, use 3 grams of glass. Assemble the apparatus as shown in Figure 2, except for the adapter and receiver. Connect the air line with glass tube B, and during a 30-minute period blow air through the ap aratus at such a rate that a steady stream of bubbles forms ine!t Mulligan wash bottle. From time to time heat the evolution apparatus with a flame, beginning a t the end
attached to H. This operation removes the moist air from the ap aratus and the water adsorbed on the glass walls. Near the en: of this period place 20 cc. of water in the receiver and insert the adapter in it as shown in Figure 2. Connect the adapter to the apparatus and change from air ressure t o suction. Regulate the rate of air flow by means o?screw clamp C, until one bubble per second forms in the receiver, and continue this rate during the remainder of the evolution procedure. Again flame the apparatus, including the ground joint on the adapter. Introduce into the digestion flask, through funnel J , 20 cc. of concentrated sulfuric acid, leaving a little acid in the funnel to serve as a seal. Mix the contents of the flask and heat it, by means of a araffin bath, a t 140' to 150" C. for 1.5 hours and at 175" C. &r an additional 1.5 t o 2.0 hours. At intervals of about 10 minutes during the evolution procedure, mix the contents of the digestion flask by shaking. If the white sublimate should form in the delivery tube, play a flame over the tube, beginning with the end near the digestion flask, until the material is entirely forced into the adapter. At the end of the y c e d u r e attach pinchcocks N and I , open the stopcock on unnel J , and disassemble the apparatus. Rinse the adapter, includin the silicic acid collected on its lower end, and the contents of the receiver into a flask, dilute the solution to about 200 cc., heat to boiling for 5 minutes, and add a few drops of phenolphthalein. Convert the fluorine combined as hydrofluosilicic acid in the solution to sodium fluoride by adding approximately 0.1 N sodium hydroxide until the alkaline color of the indicator persists on further boiling. Cool the solution in the stoppered flask and determine its fluorine content by the colorimetric method described in the previous paper (9). In a blank determination, 1.3 CC. of 0.1 N sulfuric acid collected in the receiver-an amount of sulfate which is without influence on this method. It is probable that the receiver contents could be analyzed by thorium nitrate titration procedure developed by Willard and Winter (9) or as modified by this writer (3). TABLE I. ANALYSIS OF SODIUM FLUORIDE No. SAMPLE F SOUQET
TIMEAND TEMPERATURE TION PERIOD
EVOLU-
F FOUND F RECOVERED
%
Gram 0.0860 0.1182
Gram 0.0389 0.0534
Gram 0.0390 0.0535
100.25 100.18
3 hrs. at 175' 1.5 hrs at 140;;f3;9 2.5 hrs. at
7 8 9 10
0.0639 0.0488 0.0841 0.0986 0.1100 0,0984 0.0882 0.0957
0.0289 0,0220 0.0380 0.0446 0.0498 0.0445 0.0399 0.0432
0.0290 0.0217 0,0380 0.0445 0.0500 0.0445 0.0400 0.0432
100.34 98.63 100.00 99.77 100.40 100.00 100.25 100.00
11 12
0.0867 0.1226
0.0392 0.0554
0.0392 0.0555
100.00 100.18
Same Same Same Same Same Same Same 1 hr. at 140-150°, 1.5hrs. at 175' Same Same
Average
100.00
1 2
I 1 0
3 4 5 6
The results presented in Table I were obtained by analyzing "Baker's c. P. Analyzed Sodium Fluoride," the same
September 15, 1933
INDUSTRIAL AND ENGINEERING
material being used in the preparation of the standard fluorine solution required in the colorimetric procedure. DISCUSSION The white sublimate collected several times in the delivery tube in analysis No. 1 and once in No. 2 in the first 1.5-hour period when the temperature was inadvertently allowed to rise considerably over 150' C. I n both determinations the substance 'il" successfully driven into the adapter by flaming the tube. I n analyses 3 to 9, inclusive, very little, if any, of the material was collected; nevertheless, the tube was flamed. I n analyses 10 to 12, inclusive, the sublimate did not form and the tube was not heated. It thus appears that the formation of this substance can be prevented by maintaining the temperature of the digestion flask a t less than 150' C. for the first 1.5 hours of the evolution procedure and that the material can be driven into the receiver as described. It is possible that the appearance of the sublimate during the first period at temperatures above approximately 150" C. may be due to the liberation of water from sulfuric acid or its hydrate. That the substance does not accumulate during the second period in which the digestion flask is heated to 175" C. may be due to the silicon tetrafluoride having already been completely evolved. The results given in Table I1 were obtained by analyzing for fluorine in the presence of certain impurities. The standard fluorine solution m-as prepared from synthesized sodium fluoride whose purity was checked by conversion to sodium sulfate. I n analyses Nos. 4 to 7 , inclusive, water collected in the delivery tube during the preliminary drying period probably because the so-called tricalcium phosphate
CHEMISTRY
317
was a t least partially hydroxy-apatite, which was dehydrated by the heat. The drying period and the flaming of the tube were continued until the water was entirely expelled from the apparatus and no more collected. The white sublimate collected a t least once in each of these determinations and was driven into the adapter as already described. TABLE11. ANALYSISOF IMPURE FLUORIDES NO.
CaFP MATERIAL ANALYZED SAMPLEF SOUQHT F FOUND F RECOVERED GTam
Y"
0.1028 0.0474 (1.11-149 0.0483 0.0443 0.0599 0.0593 0.0396
0.0474 0.0484 0.0442
100 IO0
0,0330
0.0329
Gram
CaFz CaFs
a
Cram
,I
100.20 99.77 100,33 99.82
0.0601
0.0592 0,0399
100.75
99.76
Bureau of Standards Sample No. 79. CPFZcontent 94.83 i 0.25%.
LITERATURE CITED (1) Adolph, W. H., J . Am. Chem. SOC., 37,2500-15 (1915). (2) Armstrong, W. D., IND. ENG.CHEM.,Anal. Ed., 5, 300 (1933). (3) Armstrong, W. D., J . Am. Chem. Soc., 55, 1741-2 (1933). (4) Casares, J., Anales soc. espafi. fts. qutm (technica), 27, 290-301 (1929). ( 5 ) Reynolds, D. S., Ross, W. H., and Jacob, K. D., J . Assoc. Oficial Agr. Chem., 11, 225-36 (1928). (6) Shuey, G. A.,Ibid, 14,126-32 (1931). (7) Treadwell, F. P., and Koch, A. A,, 2. anal. Chem., 43, 469-506 (1904). ( 8 ) Wagner, C. R., and Ross, W. H., I N D .E N G .CHEM.,9, 1116-23 (1917). (9) Willard, H. H., and Winter, 0. B., Ibid., Anal. E d . , 5, 7-10 (1933). RECEIVED May 29, 1933
Adsorption of Alcohol by Fibrous Materials' R. T. MEASE,Textile Section, Bureau of Standards, Washington, D. C.
T
HL4T textile fibers adsorb water and hold it rather tenaciously is common knowledge, but it does not appear to be generally recognized that other liquids may be adsorbed and held in considerable amounts even a t elevated temperatures. ilnalytical procedures sometimes call for the quantitative extraction of specimens placed in paper thimbles. The amount of extracted material is then obtained from the weights of the dried thimble before and after extraction. I n some methods for the analysis of textiles and the purification of fibers, the final operation is to rinse or extract the specimen with alcohol or other solvent to remove nonfibrous materials and expedite drying. The purpose of this note is to call attention to the fact that fibrous materials in the form of paper extraction thimbles, cotton, wool, silk, and rayon adsorb alcohol and hold an appreciable amount of it, even when dried to constant weight a t temperatures considerably above the boiling point of alcohol. The adsorption of alcohol by silk has previously been noted and just recently a study was made of the retention of polyalcohols by cellulose (I,2 ) . The cotton, wool, silk, and rayon used in these experiments were carefully freed from nonfibrous materials by appropriate methods. Whatman extraction thimbles and a commercial weighted silk cloth were also used. Specimens were dried to constant weight in an air bath a t 105" to 110" C. and then immersed in freshly distilled absolute ethyl alcohol 1
a t 70" C. for 15 minutes, removed, and again dried to constant weight. The increase in weight, expressed as a percentage of the weight of the oven-dried specimen-that is, the amount of alcohol adsorbed-is recorded in the table. FIBER
% Cellulose : Viscose rayon Cotton Whatman extraction thimble
2.8
1.8
0.9
1.8
0.7 1.8
When specimens containing alcohol were rinsed with boiling or even warm water, centrifuged, and dried, they returned to their original weight. When treated again with alcohol a t any temperature and dried they increased in weight and on rinsing with water and drying returned to within 0.1 per cent of their original weight. Similar experiments with diethyl ether, chloroform, carbon tetrachloride, trichloroethylene and Stoddard solvent (used in dry-cleaning) in place of alcohol did not result in an increase in weight of any of the fibers. LITERATURE CITED (1) Anonymous, Bur. Standards, Tech. News Bull. 165, 4 (January, 1931). (2) Shutt, Richard S., and Mack, Edward, J r . , IND,ENG.CHEX., 25, 687-91 (1933).
Publication approved by the Director of the Bureau of Standards of the
U. S.Department of Commerce.
ALCOHOL ADSORBED
RECEIVED June 22, 1933.
