November, 1928
ISDL-STRIAL A.VD EAVGIiVEER1SGCHE-VISTR Y
beakers for 10- and 15-minute periods, respectively. The chlorinated wood samples were given the usual sulfurous acid treatment, were extracted with 2 per cent sodium sulfite solution, and the yield of chlorinated residue was determined as previously described. Yields of 78.4 and 65.2 per cent, respectively, were obtained. These two yield points, while they are not shown in the graph because the procedure for moistening the sawdust, through which the points were obtained, is different from that usually followed in the analytical method, would fall fairly close to the yield curve in Figure 1 indicating that thorough and uniform penetration of the wood is necessary in order to secure maximum action of the chlorine gas. The results of the investigation make it clearly apparent that the amount and the uniformity of distribution of the moisture in the sample are of great importance in the chlorination of wood. The apparent discrepancies of the first chlorinations are thus explained. Incidentally, upon repeating the large-scale experiments just described. using %gram quantities in which the wood was chlorinated by forcing chlorine gas up through the moist material contained in a Jena (fritted-glass-bottom) crucible, it was found that a yield of 66.8 per cent was obtained after one 10-minute chlorination period. This fact shows that more efficient chlorination takes place when the sample is
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chlorinated in this manner than ensues when the sawdust is chlorinated in a beaker. Summary
L4study of the chemistry of the Cross and Revan ce!.lulose determination method has shown that for spruce wood the reaction involved follows the same general course taken by the reactions occurring with the ordinary pulping reagents, but that both higher yields and greater delignification result. The experiments show that, for spruce wood, lower yields of cellulose are obtained from the oven-dried residues than froni the original wood, that lignin is not completely removed, even after a number of protracted chlorinations, and that some of the pentosans in the cellulose are removed during the first and each succeeding chlorination, while the pentosans not iii the cellulose are destroyed very rapidly during the process of cellulose isolation. The fact that the pentosans in the cellulose do not increase in the various steps of the chlorination process indicates that furfural-yielding bodies are not formed by the decomposition of cellulose during chlorination. To secure maximum reactivity, the sample of spruce to be chlorinated should contain a quantity of water at least equal to its own weight, evenly distributed through the wood. Presumably, the yield of chlorinated residue may be controlled by the amount of moisture in the sample.
Inaccuracies in Determination of Acidity of Raw Rubber by Water Extraction’ A. D. Cummings and H. E. Simmons UIVIVERSITY OF B ~ R O N AKRON, , OHIO
URIKG the course of an investigation on ultra-accelerators the basic rubber-sulfur-zinc oxide mix used for curing experiments showed a maximum tensile of 126.5 kg. per sq. cm. A mix of rubber 100, sulfur 10, with no zinc oxide, showed a tensile of less than 84.5 kg. per sq. cm. This was so low that it seemed desirable to investigate further. The first hypothesis was that the increase in tensile brought about by zinc oxide was due, not only to the reenforcing effect of the pigment, but also to the neutralization of excess acid in the smoked sheet. To determine the water-soluble acids in rubber a common method has been to extract the rubber with hot water in much the same manner as the conventional acetone extraction, This was done with the rubber in question, but failure to obtain consistent values for acid numbers led to a critical examination of the method and the conclusion that hydrolysis of esters in the rubber by the hot water can take place. The result is a very high value for water-soluble acids. To avoid all trouble, it is best to employ the procedure used by Van Rossem and Dekker* where the rubber is first extracted with acetone and the acetone extract then digested with water a t low temperature to determine water-soluble acids.
D
Experimental
Three sampies of the smoked sheet mere extracted for 8 hours with hot water and then for 8 hours with acetone. The acid numbers3 obtained are shown in Table I. 1 Presented under the title “Determination of Acidity of Raw Rubber by Water Extraction” before the Division of Rubber Chemistry a t the 75th Meeting of the American Chemical Society, St. Louis, Mo., April 16 to 19, 1928. 2 IND. ENQ.CHEH., 18, 1152 (1926). 8 Whitby and Winn, J . SOC.Chem. I n d . , 42, 336T (1923); Whitby, Trans. I n s f . Rubber I n d . , 1, 12 (1925); Whitby and Greenberg, IND. ENG. CHEW.. 18, 1168 (1926).
Table I-Acid Water extract Acetone extract
Numbers of Water and Acetone Extracts SAMPLEI SAMPLEI1 SAMPLE111 291 ( M ) 130 ( M ) 273 ( M ) 292 ( N ) 292 (1x7) 289 ( N )
These results indicated an unusually high acid content of the rubber. However, the one low value (130) caused suspicion. The three samples having been extracted a t the same time, there seemed to.be no explanation for this failure to get check results. T o test the method, a specimen of first latex crepe was selected and water extraction of samples cut from this was carried out. The acid numbers varied from 50 to 175 on six samples. From this it appeared that something more than simple extraction of water-soluble acids was taking place. In the hope of finding plausible explanation for this condition the procedure outlined by Van Rossem and Dekker was carried out. I n this process the rubber is first extracted with acetone; water-soluble acids are then determined by water extraction of this acetone extract on a water bath until further extraction shows no increase in acidity. Table 11-Acid Numbers by Van Rossem and Dekker’s Method A B-Total acid number of acetone extract A-Water-soluble free fatty acids (water extraction of acetone extract a t temperature of water bath) B-Liquid and solid free fatty acids (acetone-soluble only) S S - 1 S m o k e d sheet used in mixes giving low tensile S S - 2 S m o k e d sheet known to give good tensile properties in a rubbersulfur mix ACETONE ACETONE EXTRACT EXTRACT AFTER A BOILED16 BOILEDWITH HOURS WITH WATER. WATER A + B A B 8 hours 6 hours ss-1 342 53a 289a more SS-1 (extract air - dried 1 month) 273 60 187 ss-2 248 42 ( X ) 206 64 33 Water extraction first Acetone extraction (16 hours) following ss-2 . 489 399c 238b Compare values ( M )Table I. b Compare values ( N ) Table I . c Compare value ( X ) above.
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IiYD UST R I A L AND EXGINEERIKG CHEMISTRY
Colored solutions were titrated electrometrically. Some titrations were made with alcoholic potassium hydroxide standardized against pure stearic acid. Water solutions were referred to sodium carbonate as ultimate standard. All solutions were cross-checked to eliminate possible errors. I n all cases duplicate acid numbers checked satisfactorily within the limits of experimental error. The average results are shown in Table 11. This shows that boiling the acetone extract with water increases the acid number. It seemed as if a similar effect ought to be noted on very long heating with water on the steam bath. On testing this, the results in Table I11 were obtained. of Long Heating with Water ACID&-UMBER Water extraction of acetone extract SS-1 53 Extracted 12 hours on boiling water bath 53 Residue from C boiled with water 6 hours 97 Table 111-Effect
A
C
D
Discussion
The value A in Table I1 for SS-1 should agree with -11in Table I, as both are supposed to be measures of water-soluble acids only. Value B (Table 11,SS-1) agrees with X (Table I) as it should, because both measure acetone-soluble acids only. I n the case of SS-2 in Table 11, the value A(42) should equal the values (489, 399) obtained by direct water extraction if nothing is happening except simple extraction. To determine whether a similar effect could be noted in extracting an acetone extract with water, several acetone extracts were boiled with water as indicated. I n every case the acid numbers increase with time of boiling. However. as Table I11 shows,
1’01. 20, KO. 11
the water must be near the boiling point, for no effect on the acidity was noted by heating a fresh acetone extract with water for 12 hours on a water bath, but the residue from this water extraction gave an increase in acid number of 97 when boiled with water. Conclusion
From the results obtained it is concluded that the boiling water hydrolyzes some of the esters in the acetone extract. I n the case of direct extraction of the rubber with water. hydrolysis of esters must take place in the rubber, forming Tvater-soluble acids; or else, although the esters are practically insoluble in the water, it extracts a little ester each time the extraction thimble empties (Bailey-Walker apparatus), carrying the ester down to be hydrolyzed in the boiling water below. Temperature and time of heating play a prominent part. The temperature must be close to the boiling point and the acidity increases progressively with time of heating. The fact that temperature is so important in producing this effect accounts for the erratic values obtained by direct water extraction. On the electric hot plates used water did not always boil steadily, and that contained in the thimble might vary considerably in temperature, much of the time not being hot enough to hydrolyze or extract any ester. Therefore, to avoid any difficulty in the determination of water-soluble acids in rubber, extract first with acetone. then digest this extract with water on a boiling water bath until no increase in acidity of the water extract is obtained. This is a part of the procedure developed a t the Netherlands Government Institute by T7an Rossem and Dekker.
Heating Value of Coal in Nickel-Lined Bombs’ A. E. Stoppel and E. P. Harding UNIVERSXTY
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OF
MINNBSOTA, hfINNEAPOLIS,
T IS generally known that the nitric and sulfuric acids formed during the combustion of coal in an oxygenbomb calorimeter having a nickel !ining do not appear entirely as such in the bomb washings, but partially or completely attack the lining and appear either wholly or in part as nickel nitrate and nickel sulfate a t the completion of the determination. Thus, when the washings are titrated, too little acid is found, and the thermal correction for acidity is likewise too low when the usual methods for making the correction are applied as in the case of a non-corrosive bomb lining. Furthermore, unless some correction is made for the corrosive effect of the acids upon the lining, another source of error is introduced. Olin and Wilkinsz showed that the sum of these two errors, if neglected, may lead to heating values which are over 2 per cent too high for coals containing about 4 per cent of sulfur. Later, a study of the corrosion on monel-metal bombs was made by Geniesse and Soop,3 who developed a correction to be applied to the observed heating value, based on the titration of the bomb washings for free acid, and the total sulfur in the coal. They showed that by making such a correction it was possible to reduce the error to less than 0.4 per cent in the case of monel-metal bombs, and suggested that a similar correction would be applicable for nickel-lined bombs. 1 2
3
Received April 12, 1928. Ckem. Mer. Eng., 26, 694 (1922) IND. E m . CHEM, 17, 1197 (1926).
MI”.
Proposed Method for Determining Corrosion in KickelLined Bombs
The writers have found it possible to determine the amount of corrosion in nickel-lined bombs with a sufficient accuracy for technical purposes by titrating the bomb washings with a standard sodium hydroxide solution, using two indicators, methyl red and phenolphthalein, both of which are available in any laboratory where the heating Talue of coal is determined by means of an oxygen bomb calorimeter. The bomb washings are boiled 2 or 3 minutes to remove carbon dioxide, after which methyl red indicator is added and the solution is titrated with 0.1 ATsodium hydroxide solution. This measures the total amount of free acid present. About 1 cc. of phenolphthalein is then added and the titration continued until the red color of the phenolphthalein shows through the yellow of the methyl red. This end point, however, disappears on boiling the solution. More alkali is added until the indicator is again colored, after which the solution is again boiled. The end point to be taken is the one a t which a rather strong red color is permanent after 2 or 3 minutes of brisk boiling. This may best be seen by allowing the greenish precipitate of nickel hydroxide to settle and observing the supernatant liquid. I n the case of large quantities of nickel sulfate or nitrate this may require five or six subsequent additions of alkali and boilings before a permanent end point is reached. After a little practice the titration can be made fairly rapidly. The reactions for
