DECOMPOSITION CURVES OF SOME NITROCELLULOSES.
271
Zeisel's method. Found: 10.78 and 1 I . j o per cent. of Z,H,O. C a h latcd: 11.54per cent. of C,H,O. The ester forms an acetyl derivative, hut this and several other derivatives of iiiarrubiiri will be reported upon in my next paper. The results of the investigation so far show t h a t marruhiin is a lactone behaving like a 7-lactone in t h a t it easily takes up a molecule of water and changes 'io a hydroxy acid. The formulae of marrubiin. niarruhic acid and ethyl marrubate can therefore be written as follows:
FHzSOz- CO , CzoH,O,(OH) .COOH , I L-0 'The investigation is continued.
Cz,H,O,(OH) COO.C&&.
N O R T H W E S T E R N U N I V E R S I T Y S C H O O L OF P H A R M A C Y ,
CHICAGO.
DECOMPOSITION CURVES O F SOME NITROCELLULOSES OF AMERICAN MANUFACTURE.' BY OSWIN W. WILLCOX. Received Xoveniber I I , 1907.
In the course of a study of the test proposed by Obermuller2 for the stability of nitrocellulose, it was observed t h a t the rate of decomposition of a n ordinary collodion cotton during a given period of time depended on whether or not the gaseous products of decomposition had been allowed to remain in contact with the sample during previous periods. As the Obermuller apparatus is perhaps the most accurate and convenient ireans yet devised for following quantitatively the progress of the decomposition of a nitrocellulose a t temperatures below its ignition point, some of the results obtained are deemed of interest. Obcm?uller's test is essentially as follows: A weighed quantity of the nitrocellulose t o be tested is placed in a glass tube, which is then evacuated by means of a good air pump. When the air has been removed as much as possible, the tube is plunged into a bath previously brought to a standard temperature, which is maintained constant throughout thc duration of the test. The nitrocellulose in the tube immediately begins to decoinpose and t o give off gaseous products; the tube being in connection with a mercury manometer, the rate a t which the products of decomposition are evolved is measured by the increase of pressure shown hj. the manometer. This rate will naturallv be greater for nitrocellulosc of poor stability and less for nitrocellulose of good stability. M'orking a t a standard temperature of 140' C., and with a tube which, with its connections, had a ~-01uineof 37 cc., Oberniuller
' Published
by permission of the Honorable the Secretary of Wa.r. Mittheilung atis dem Berliner Bezirksvarein des Vereins deutscher Chemiker, October I I , I 904.
oswm w.
272
WILLCOX.
found that one gram of a stable nitrocelluloscx does not cause in one hour a greater increase of pressurc than I O O inw. of inercur!-. The apparatus employed is diagrammatically shown in Figs. I and 2 , which are copied from Oberinullcr's paller. 'I'hc decomposition tubc
c Figs.
I
and
2.
is of glass and of about 1 2 cc. capacity; the top of 2 is ground t o fit the larger end of T, b y means of which it is connected to the rnanonieter M. Behind the manorcter is a scale S. By means of the side tube K the drcon:position tube can be put in communication with the air pump. 1. is a glass bottle, on either side of which is R glass stopcock (H and H'). The lower part of the nianonetcr is connected with the mercury reseri.oir G. The bath, I,, which may consist of a saturated solution of calcium chloride, or, better, of oil, such as is used in the cylinders of locomotives, serves t o heat the tube 2. The shect-iron case K, which is provided with a window of heavy glass, semcs to protect t h e operator from possible explosions. In Fig. 2 is shown an enlarged sketch of the tube Z and its connections. G is a glass rod sealed by its upper end to 1';the object of this rod is to hold the nitrocellulose in place in the lower end of 2. X is a mark I cm. under the cap. The method of procedure adopted in this study is as follows: Exactly 2 granis of the nitroccllulose previously dried by heating for I hour at 100' were placed in the decomposition tube 2 ; any nitrocellulose 2 (Fig.
I)
273
DECOMPOSITION CURVES O F SOME NITROCELLWLOSES.
adhering t o the walls of the tube were swept down by means of a small wad of pure dry absorbent cotton, which was allowed t o remain in the tube during the heating. The tube was then fitted in place and evacuated as conipletely a s possible, usually down t o a n internal pressure of less than j mm. of mercury. The bath having been brought t o 140’ the positions of the mercury in both limbs of the manometer were noted, all stopcocks were closed and the tube lowered into the bath up t o the mark X, the time being noted a t the same instant. Exactly I j ri-inutes from the time of immersing the tube, the surface of the mercury in t h e left limb of the manometer was brought back t o its original position and the rise of the mercury in the right limb was noted; and this was repeated a t intervals of Ij niinutes until four such readings had been taken. The accumulated gases were now pumped out’ and a vacuum maintained in the tube for I j niinutes. At exactly 7 5 minutes from the time of beginning all stopcocks were again closed and the gaseous products of decomposition allowed t o accuniulate for a period of 15 minutes. The pressure developed during these 1.j minutes was read, the tube again kept vacuous for I j minutes, and EO on alternately for j hours from the tinie of beginning. For convenience in discussion, the whole t i n of heating n a y be regarded as divided into periods of I j minutes each. During the first four periods the gases were allowed t o accumulate in the tube and t o exert pressure; after the first hour the gases were being continually withdrawn during the odd periods, whereas they were allowed to accumulate during the even periods. The procedure followed during the first hour will be referred to as “test with increasing initial pressure,” and t h a t followed after the first hour as “test with constant initial pressure.” All readings of pressure are given as millimeters of mercury per gram of substance. The data obtained are tabulated .in Table I. TABLEI. No. of
sample,
Pressure i n nim. of mercury per period of 15 minutes. Test with increasing initial pressure. Test with constant initial pressure, I
1st. 2920
3831 3883 3863 3607 3608 3609
2nd.
3rd.
20.3 23.9 28.7 18.7 23.4 27.7 1 8 . 6 22.2 27.8 21.0 29.5 35.0 2 1 . 9 24.5 28.7 19.2 20.9 24.6 1 8 . 1 22.2 25.8
4th.
6th.
8th.
10th.
12th.
14th.
16th.
18th.
20th.
32.9 33.0 32.0 42.7 34.2 29.1 25.8
27.8 27.7 27.6 38.0 31.5 25.5
28.6 28.7 28.2 39.7 33.5 27.0
30.6 30.6 30.3 41.8 34.1 28.1 28.5
31.0 31.3 30.6 43.3 34.5 29.1 28.3
33.5 33.7 32.2 45.7 36.7 29.7 29.5
33.0 32.7 32.5 45.7 36.2 31 7 29 7
33.5 34.5 33.0 47.0 39.0 31.5
3a.o 34.5 33.5 47.5 38.0 32.5 32.0
29.4 26
I
32.0
The samples of nitrocellulose here reported on represent the product of the principal factories of the United States. They are “decanitrocelluloses” of about 12.60 per cent. nitration and 99 per cent. solubility in ether alcohol.
274
OSWIN W. WILLCOX.
The figures at the top of the columns in Table I are the numbers of the periods, of I5 minutes each, during which the gases were allowed to accumulate (it will he remembered t h a t a vacuum was maintained in the tube during the odd periods). The results are also plotted in the accompanying curves. An examination of the figures given in Table
Pig.
J.
DECOMPOSITION CURVES OF SOME NITROCELLULOSES.
27.5
,:i,, ". I .
I will show that the course of the decomposition in "t& with incrcasing initial pressure" and in "test with constant initial prcssurc" iollows different laws. In the case of sample KO. 3831, for example, t h e quarter hourly increase of pressure in the first period is 1S.7 nini., in tlic sccond 23.4 mm., in the third 27.7 mni., and in the fourth 33.0 nun., a n average constant difierence of about 4.5 nini. Hy the aid of this law of increase it may bc calculated t h a t during the sixth period tlic increase of pressure would be 42 mm., ii the gases were allowed t o accumulate in the tube without interruption. The calculated rate for the sixth period was found by experiment to be the actual rate under the condition named. I f , however, a vacuuiii be nxintained in the tuhc during the fifth period, then the increase of pressure during the sixth period is not 42 miii., but only 27.7 nini., a ditkrencc of 14.3 mni. The difference in the rates of increase oi pi-cssurc under the two conditions uicasures the catalytic effect of the presence of the p s e o u s products o i decomposition on the speed of the reactions of deconiposition. I t may be noted t h a t while reii.oval of the gases lowers the "decomposition prcssure" of the heated nitrocellulose it is not restored to the original ixluc; the initial deco:i:position pressure gradually rises with the time of heating.'
' At the Same time the heated nitrocellulose is being transformed into a modification soluble in absolute alcohol. A separate report, with quantitative data, nil1 be made on this subject in the future.
276
OSWlN W. WILLCOX.
The results reported in Table I were obtained by working a t a constant voluinc of 30 cc. I t is obvious that as the volunie of the tube and its accessories determines the concentration of the gaseous products of decomposition, the rate of increase of pressure will vary with this volume. To deduce the volutne relations of the test a number of esper-
1%
.
