Sulphuric acid 66 parts by weight.
Nitric acid 17 " "
Water 17 " "
Temperature of immersion, 30° C. Time, twenty to thirty minutes.
The cellulose is used in the form of tissue paper 2/1000 inch thick, 1 lb. to 100 of acid mixture. The nitro-cellulose produced by this formula is very insoluble in the compound ethers and other solvents of pyroxyline, and is seemingly only converted or gelatinised by the action of the solvent. The next formula produces a mixture of tetra-and penta-nitro- celluloses hardly soluble in methyl-alcohol (free from acetone), but very soluble in anhydrous compound ethers, ketones, and aldehydes:—
Nitric acid, sp. gr. 1.435 8 lbs.
Sulphuric acid, sp. gr. 1.83 15-3/4 lbs.
Cotton 14 oz.
Temperature of nitration, 60° C. Time of immersion, forty-five minutes.
The 60° of temperature is developed by mixing the acids together. The cotton is allowed to remain in the acid until it feels "short" to the rod.
The following table, due to Mr W.D. Field, shows very plainly the great variation in the time of the immersion and the temperature by seemingly very slight causes. It extends over fourteen working days, during which time it rained four days. The formula used is that given above, except that the specific gravity of the nitric acid is somewhat lower. The product obtained differs only from that produced by using nitric acid of specific gravity 1.43 in being soluble in methyl-alcohol. From 30 to 35 lbs. of pyroxyline were produced in each of the fourteen days.
A careful examination of this table will prove very instructive. The increase in yield varies from 31 per cent. to nothing, and the loss runs as high as 10 per cent., yet care was taken to make the product uniform in quality. On the days it rained there was a loss, with the exception of the fourth day, when there was neither a loss nor a gain. On the days it was partly clear, as just before or after rain, the table shows a loss in product. We can explain this fact by reason of the moisture-absorbing qualities of the cotton. On the rainy days it would absorb the moisture from the air until, when immersed in the acids, they were weakened, and the fibre dissolved more or less in weakened acid, producing what is known as "burning" in the batch. It will also be noticed that on days which show a loss, the time of the immersion was correspondingly short, as on the a loss, the time of the immersion was correspondingly short, as on the tenth, twelfth, and seventh days.
______________________________________________________________________ | | | | | | Specific Gravity. | Time. | | |_____________________|_______________________________| | | | | | | | | | |H_{2}S0_{4}.|HNO_{3}.|Hours.|Minutes.|Hours.|Minutes.| |________________|____________|________|______|________|______|________| | | | | | | | | | 1. Clear | 1.838 | 1.4249 | … | 20 | 4 | … | | 2. " | 1.837 | 1.4249 | … | 20 | 2 | … | | 3. Cloudy | 1.837 | 1.4226 | … | 45 | 2 | … | | 4. Rain | 1.837 | 1.420 | … | 20 | 1 | 20 | | 5. Clear | 1.8377 | 1.42 | 1 | 15 | 2 | … | | 6. Rainy | 1.8391 | 1.422 | … | 35 | 1 | 40 | | 7. Cloudy | 1.835 | 1.4226 | … | 20 | … | 35 | | 8. Clear | 1.835 | 1.422 | … | 35 | 1 | 10 | | 9. Partly Clear| 1.824 | 1.4271 | … | 20 | 1 | … | |10. " | 1.83 | 1.4271 | … | 10 | … | 25 | |11. Cloudy | 1.832 | 1.425 | … | 10 | … | 50 | |12. Rainy | 1.822 | 1.425 | … | 10 | … | 20 | |13. Partly CLear| 1.8378 | 1.4257 | … | 60 | 1 | 40 | |14. Cloudy | 1.837 | 1.4257 | 1 | 56 | 4 | 40 | |________________|____________|________|______|________|______|________| | | | | | |Temp., Deg. C. | Percentage | | |_______________|___________________| | | | | | | | | From | To | Increase. | Loss. | |________________|_______|_______|___________|_______| | | | | | | | 1. Clear | 57° | 62° | 31 | … | | 2. " | 60° | 62° | 18 | … | | 3. Cloudy | 60° | 62° | 7 | … | | 4. Rain | 60° | 63° | 0 | 0 | | 5. Clear | 58° | 62° | 15 | … | | 6. Rainy | 58° | 62° | … | 2 | | 7. Cloudy | 62° | 65° | … | 10 | | 8. Clear | 60° | 62° | 5 | … | | 9. Partly Clear| 50° | 60° | … | 3 | |10. " | 58° | 60° | … | 10 | |11. Cloudy | 58° | 60° | 8 | … | |12. Rainy | 58° | 60° | … | 10 | |13. Partly CLear| 50° | 58° | 20 | … | |14. Cloudy | 50° | 60° | 16 | … | |________________|_______|_______|___________|_______|
The lesson this table teaches is, that it is almost impossible to nitrate cellulose in small quantities, and get uniform results, when the nitration is carried on at high temperatures. As regards the solubility of pyroxyline, Parks found that nitro-benzene, aniline, glacial acetic acid, and camphor, dissolved in the more volatile solvents methyl-alcohol and alcohol-ether, were much the best solvents for producing a plastic, as they are less volatile, and develop greater solvent action under the influence of heat. Nitro-benzene gives a solution that is granular; it seems to merely convert the pyroxyline, and not to dissolve it; but on the addition of alcohol, a solution is at once obtained, and the granular appearance disappears, and the solution becomes homogeneous. The acid mixture and the method of nitrating have much to do with the action of the various solvents, so also has the presence of water.