NITROCELLULOSE AND CAMPHOR 131' J . B. NICHOLS
As part of my senior research in the autumn of 1922 I was asked by Professor Bancroft to determine, if possible, whether camphor peptized or dissolved the nitrocellulose known as pyroxyline. If the pyroxylin went into true solution, we could determine its molecular weight. If it did not, we had made a definite advance towards the theory of the formation of celluloid. The method employed consisted in determining whether small additions of nitrocellulose did or did not lower the freezing-point of camphor. A Beckmann thermometer was set for a range from 170' to 176'. The camphor was placed in a freezing-point tube equipped with the thermometer and a copper stirring rod; this tube was surrounded by a larger tube which gave air insulation from the bath of Crisco. As the result of several determinations, the melting-point of camphor was found to be 1 7 2 .'I or 175.5' when corrected for the error due to the emergent stem. The camphor did not have a sharp melting-point, however, and became slightly brownish after several heatings and coolings. This might be due either to pieces of cork falling into the camphor or to the copper stirring-rod, so both sources of error were eliminated. A glass stirring-rod was substituted for the copper one and the hole through the cork was protected by a short piece of glass tubing. Camphor sublimes so readily that it was found necessary to bring the level of the bath as near as possible t o the top of the tube. These changes eliminated the brownish discoloration. When pyroxylin was added, it apparently went into solution and the A quantity of bubbles was given off, freezing-point was lowered 6'4'. however, indicating the probable decomposition of the cellulose in molten camphor at 180'. The mixture solidified to a reddish-brown mass and had a sickening odor similar to that of acrolein. Another sample of camphor was melted and pyroxylin added; but the gas evolved was collected in a gassampling tube, the first IOO cc being discarded as chiefly air swept out of the freezing-point tube. The next IOO cc of gas were analyzed and were found to consist of carbon dioxide, carbon monoxide, nitric oxide, and nitrogen with no hydrocarbons and no hydrogen. This analysis agrees with that made by Pfyl and Rasenackl of the gases given off during the slow decomposition of nitrocellulose. It seems therefore safe to conclude that the gases come from the decomposition of the nitrocellulose and not from the camphor. If some substance could be added to the camphor which would lower its melting-point, it might prove possible to add nitrocellulose without decomposition, though that introduces the peculiarities of ternary mixtures. Monobrom-camphor seemed the best choice because it melts at 76' and does not Chem Zentr. (5) 13 IT, 763 (1909).
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boil until 274'. A preliminary run showed that pyroxylin has no effect on the melting-point of monobromcamphor. Since some pyroxylin seemed t,o dissolve, this showed that monobromcamphor peptizes nitrocellulose to some extent; but when more than two percent of nitrocellulose was added, the monobromcamphor peptized it with difficulty. The freezing-point curve for mixtures of camphor and monobromcaniphor was then determined and the eutectic was found to occur at 62.3' wit,h a composition of 15% camphor and 85% monobromcamphor. The data for the curve are given in Table I.
TABLE I 7oBromcamphor 0.
16.7 28.6 40.0 48.2 62.5 71.4
F.Pt. (corr.)
175.4' 157.0
142.4 127.3 114.9 91 . S 77.85
% Bromcamphor 83.3 84.0 84.7 85.5 87 . o 90.9 IO0 .o
F.Pt. (corr.)
84 .oo 63.I 5 62.5 62.3 63.7 67 .o 74.8
Since the volatilization of camphor from a mixture with monobromcaniphor would change the composition and the freezing-point, it was not safe to go above 100' and a water-bath was therefore substituted for the Crisco bath. To a mixture of 20 grams of monobromcamphor and 5 . 8 grams camphor, having a freezing-point of 7 I .2' there were added 0.2 grams of pyroxylin. A careful determination of the freezing-point gave a value of 70.8' or a lowering of 0.4'. Addition of 0.2 grams pyroxylin lowered the freezing-point another 0.4', to 70.4'. Another run was made, using a different mixture freezing at about 90', and approximately the sanie results were obtaind. These data seemed t o indicate that pyroxylin dissolves in melted camphor. Using 49800 as the cryoscopic constant for camphor, the molecular weight of the nitrocellulose came out about 4300, indicating a formula with n = 16.
It was possible, however, that this lowering of the freezing-point might be due t o moisture adsorbed by the nitrocellulose and it was calculated that this lowering of the freezing-point might be obtained if the pyroxylin contained 0.5% water. A couple of drops of water were added to a mixture of camphor and monobromcamphor freezing at 91 ,9O, and the freezing-point was lowered nearly two degrees. A one-gram sample of pyroxylin was therefore dried for a day in a vacuum deaiccator over sulphuric acid and was then reweighed. It was found to have lost the 0 . 0 0 5 grams of water which was supposed t o be present. To a mixture of 15 grams monobromcamphor and 6 grams camphor freezing a t 78.4', there were added 0.2 grams of thoroughly dried nitrocellulose. No lowering of the freezing-point could be detected and a further addition of 0.2 grams
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NITROCELLULOSE A N D CAMPHOR
77=
had also no effect. In order to check this, o . 2 grams of dried pyroxylin were added to another mixture freezing a t 9 1 .I O and no change of freezing-point could be detected. This proved conclusively that no true solution is formed and that camphor peptizes nitrocellulose. With the specially-dried pyroxylin, peptization took place almost immediately, while peptization was relatively slow with the pyroxylin containing traces of moisture. The addition of more than 7-8Yc pyroxylin (referred to camphor) rendered the mixture so viscous that no definite freezing-point could be determined. The general results of this work are:I . Pyroxylin decomposes when added to melted camphor, yiclding carbon dioxide, carbon monoxide, nitrogen, and acrolein. 2 . Monobromcamphor peptizes pyroxylin slightly. 3. The camphor-monobromcamphor freezing-point curve has been determined. The eutectic temperature is 62 . 3 O and the eutectic composition 85yo monobromcamphor. 4. Small amounts of moisture in nitrocellulose decrease the rate of peptization by camphor. 5. Nitrocellulose does not lower the freezing-point of camphor. Camphor, therefore, peptizes pyroxylin and does not carry it into true solution. Cornell Unioersity.
