Dietz and Wayne (U.S.P., No. 133, 969) use ramie, rheca, or China gra.s.s for producing a soluble pyroxyline. That made from ramie is always of uniform strength and solubility, and requires a smaller quant.i.ty of solvent to dissolve it than that made from cotton. Mr Field's experience, however, is entirely contrary to this statement. Such is the influence of the physical form of the fibre on the process of nitration, that when flax fibre and cotton fibre are nitrated with acid mixtures of exactly the same strength, and at the same temperature, the solution of the first is glutinous or thick, and the second fluid or thin. By simply nitrating at a higher temperature than the cotton, the flax will yield a pyroxyline giving an equally fluid collodion.

The presence of chlorine in the fibre must be carefully avoided, as such a fibre will yield an acid product which cannot be washed neutral. The fibre must be dry before nitration; and this is best done, according to Mr Field, by using the form of drier used in drying wool.

~Nitration of the Fibre.~--Mixed cotton and flax fibre in the form of paper, from 2/1000 to 3/1000 inch thick, and cut into 1-inch squares, is nitrated by the Celluloid Manufacturing Company, and the same paper, left in long strips, 1 inch wide, is used for nitration by the Xylonite Manufacturing Company, of North Adams, Ma.s.s. (U.S.A.).

The Celluloid Company introduce the cut paper into the mixed acids by means of a hollow, rapidly revolving tube, flared at the lower end, and immersed in the mixed acids. The centrifugal force of the revolving tube throws the paper towards the sides of the vessel, leaving the centre of the vessel ready for fresh paper.

The Xylonite Company simply cut the paper into long strips, and introduce it into the mixed acids by means of forks. The arrangement used by this Company for holding the mixed acids is a cylindrical vessel divided into a number of sections, the whole revolving like a turntable, thus allowing the workman to nitrate successively each lot of paper at a given point.

This Company did not remove the acid from the paper after its immersion, but plunged it immediately into the water, thus losing a large proportion of the waste acid. The Celluloid Company, by using the paper in smaller pieces, and more paper to a pound of acid, and wringing the mixed acid from the paper before immersion in water, had a better process of nitration.

Other manufacturers use earthenware vessels, and gla.s.s or steel rods, hooked at one end, having small pieces of rubber hose pulled over the other end to prevent the hand from slipping. The form of vessel in general use is that given in Fig. 23. It is large enough to nitrate 1 lb. of cotton at a time. The hook at one end of the rod enables the workman to pull the pyroxyline apart, and thus ensures saturation of the fibre. In the winter the room in which the nitrating is done must be kept at a temperature of about 70 F. in order to secure equality in the batches.

[Ill.u.s.tration: FIG. 23.--VESSEL FOR NITRATING COTTON OR PAPER.]

The nitrating apparatus of White and Schupphaus (U.S.P., No. 418, 237, 89) Mr Field considers to be both novel and excellent. The cage (Fig. 24), with its central perforated cylinder (Fig. 25), is intended to ensure the rapid and perfect saturation of the tissue paper used for nitrating. The patentees say that no stirring is required with their apparatus. This, says Mr Field, might be true when paper is used, or even cotton, when the temperature of nitration is from 30 to 35 C., but would not be true if the temperature were raised to 50 to 55 C. The process is as follows:-- The paper is nitrated in the cage (Fig. 25), the bottom of which is formed by the f.l.a.n.g.ed plate C, fastened to the bottom of the internal cylinder B.

After nitration the cage is carried to a wringer, which forms the basket, and the acids removed. Finally, the cage is taken to a plunge tank, where the paper is removed from the cage by simply pulling out the central perforated cylinder B. Fig. 26 shows the nitrating pot, with its automatic cover. The plunge tank is shown in plan and section in Figs. 28 and 29.

This apparatus is suitable for the nitration of cotton fibre in bulk at high or low temperatures. Other methods that have been patented are Mowbray's (U.S.P., No. 434, 287), in which it is proposed to nitrate paper in continuous lengths, and Hyatt's (U.S.P., No. 210, 611).

[Ill.u.s.tration: FIG. 24.--CENTRAL PERFORATED CYLINDER.]

[Ill.u.s.tration: FIG. 25.--THE CAGE. WHITE AND SCHUPPHAUS' NITRATING APPARATUS.]

[Ill.u.s.tration: FIG. 26.--CELLULOID NITRATING POT.]

[Ill.u.s.tration: FIG. 27.--ANOTHER VIEW.]

[Ill.u.s.tration: FIGS. 28, 29.--PLUNGE TANK, IN PLAN AND SECTION.]

~The Acid Mixture.~--Various formulae have been published for producing soluble nitro-cellulose. In many instances, although the observations were correct for the single experiment, a dozen experiments would have produced a dozen different products. The composition of the acids used depends upon the substance to be nitrated, and the temperature at which the nitration will be worked. Practically there are three formulae in general use--the one used by the celluloid manufacturers; another in which the cotton is nitrated at high temperatures; and a third in which the temperature of the immersion is low, and the time of nitration about six hours. Of the three, the best method is the last one, or the one in which the cotton is immersed at a low temperature, and then the reaction allowed to proceed in pots holding from 5 to 10 lbs. of cotton. The formula used by the celluloid manufacturers for the production of the low form of nitrated product which they use is:--

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 quant.i.ties, 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 h.o.m.ogeneous. 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.

Dr Schupphaus found that propyl and isobutyl alcohols with camphor were active solvents, and the ketones, palmitone, and stearone in alcohol solution, also alpha- and beta-naphthol, with alcohol and anthraquinone (diphenylene diketone) in alcoholic solution, and also iso-valeric aldehyde and its derivatives, amyliden-dimethyl and amyliden-diethyl ethers.

August Sayer (U.S.P., No. 470,451) finds diethyl-ketone, dibutyl-ketone, di-pentyl-ketone, and the mixed ketones,[A] methyl-ethyl, methyl-propyl, methyl-butyl, methyl-amyl, and ethyl-butyl ketones are active solvents of pyroxyline; and Paget finds that although methyl-amyl oxide is a solvent, that ethyl-amyl oxide is not.

[Footnote A: Ketones are derived from the fatty acids by the subst.i.tution of the hydroxyl of the latter by a monad positive radical. They thus resemble aldehydes in const.i.tution. The best-known ketone is acetone CH_{3}CO.CH_{3}. Mixed ketones are obtained by distilling together salts of two different fatty acids. Thus pota.s.sic butyrate and pota.s.sic acetate form propyl-methyl-ketone--

C(C_{2}H_{5})H_{2} | CO.CH_{3}]

The solvents of pyroxyline can be divided into general cla.s.ses--First, those which are solvents without the aid of heat or solution in alcohol; second, those that are solvents when dissolved in alcohol. These solvents are those which also develop a solvent action when heated to their melting point in combination with pyroxyline.

Mr W.D. Field groups the solvents of pyroxyline into cla.s.ses thus: Two of the monohydric alcohols; compound ethers of the fatty acids with monohydric alcohols, aldehydes; simple and mixed ketones of the fatty acid series. These four cla.s.ses include the greater number of the solvents of pyroxyline. Those not included are as follows:--Amyl-nitrate and nitrite, methylene-di-methyl ether, ethidene-diethyl ether, amyl-chloracetate, nitro-benzene and di-nitro-benzene, coumarin, camphor, glacial acetic acid, and mono-, di-, and tri-acetin.

Richard Hale uses the following solvent:--Amyl-acetate, 4 volumes; petroleum naphtha, 4 volumes; methyl-alcohol, 2 volumes; pyroxyline, 4 to 5 ounces to the gallon of solvent. Hale used petroleum naphtha to hasten the drying qualities of the varnish, so that it would set on the article to be varnished before it had a chance to run off. It is, however, the non-hygroscopic character of the solvent that makes the varnish successful. This formula is very largely used for the production of pyroxyline varnish, which is used for varnishing pens, pencils, &c., also bra.s.s-work and silver-ware.

The body known as oxy-cellulose[A] is formed by the action of nitric acid upon cellulose when boiled with it. The quant.i.ty formed is about 30 per cent. of cellulose acted upon. When washed free from acid, it gelatinises.

It is then soluble in dilute alkalies, and can be reprecipitated from solution by alcohol, acids, or saline solutions. Messrs Cross and Bevan a.s.sign to it the formula C_{18}H_{26}O_{16}. It dissolves in concentrated sulphuric acid, and with nitric acid forms a nitro body of the formula C_{18}H_{23}O_{16}3(NO_{2}), which is prepared as follows:--The gelatinous oxy-cellulose is washed with strong nitric acid until free from water, and is then diffused through a mixture of equal volumes of strong sulphuric and nitric acids, in which it quickly dissolves. The solution, after standing for about an hour, is poured in a fine stream into a large volume of water, by which the "nitro" body is precipitated as a white flocculent ma.s.s. The product, after drying at 110 C., was found upon a.n.a.lysis to contain 6.48 per cent. nitrogen.

[Footnote A: "On the Oxidation of Cellulose," by C.F. Cross and E.J.

Bevan, _Jour. Chem. Soc._, 1883, p. 22.]

MISCELLANEOUS NITRO-EXPLOSIVES.

~Nitro-Starch.~--It is only recently that, by means of the process introduced by the "Actiengesellschaft Dynamit n.o.bel," it has been possible to make this explosive upon the manufacturing scale. Nitro-starch has been known since 1883, when Braconnot discovered it, and called it xyloidine.

Its formula is C_{6}H_{8}O_{3}(NO_{3})_{2}, but Dr Otto Muhlhausen has lately succeeded in preparing higher nitrated compounds, viz.:--

(_a._) C_{6}H_{7-1/2}O_{2-1/2}(NO_{3})_{2-1/2}.

(_b._) C_{6}H_{7}O_{4}(NO_{3})_{3}.

Or doubling the molecule of starch:--

Nitrogen.

i. Tetra-nitro-starch C_{12}H_{16}O_{6}(ONO_{2})_{4} 11.11 per cent.

ii. Penta-nitro-starch C_{12}H_{15}O_{5}(ONO_{2})_{5} 12.75 "

iii. Hexa-nitro-starch C_{12}H_{14}O_{4}(ONO_{2})_{6} 14.14 "

He regards them as true ethers (esters) of nitric acid. Thus on treatment with sulphuric acid, these compounds yield NO_{3}H, the residue O.NO_{2} thus appearing to be replaced by the sulphuric acid residue. On treatment with a solution of ferrous chloride, nitric oxide and "soluble" starch are regenerated. On shaking with sulphuric acid over mercury, all the nitrogen is split off as NO.

Tetra-nitro-starch is prepared upon the large scale as follows:--A quant.i.ty of potato-starch is taken and exposed in some suitable desiccating apparatus at a temperature of 100 C. until all the moisture which it contains is completely driven off. It is then reduced to a fine powder by grinding, and dissolved in nitric acid of specific gravity 1.501. The vessel in which this solution is accomplished is made of lead, and must be provided with two jackets, cooled by means of water. It should further be fitted with a screw-agitator, in order to keep the nitric acid circulating freely. The charge of starch is introduced through an opening in the cover of this digesting vessel, and the proportions of acid to starch are 10 kilogrammes of starch to 100 kilos. of acid. The temperature is kept within the limits 20 to 25 C. When the solution of the starch is complete, the liquid is conducted into a precipitating apparatus, which is also provided with a cooling jacket, for the purpose of regulating the temperature. The bottom of this vessel is double and perforated, and here is placed a layer of gun-cotton to act as a filter. This vessel is filled with spent nitro-sulphuric acid obtained as a waste product from the nitro-glycerine manufactory, and the solution of starch in nitric acid is sprayed into it through an injector worked by compressed air, whereby the nitro-starch is thrown down in the form of a fine-grained powdery precipitate.

In order to precipitate 100 kilos. of the acid solution of starch, it is necessary to employ 500 kilos. of spent nitro-sulphuric acid. As it is precipitated the nitro-starch collects on the gun-cotton filter, and the acid liquor is run off through a tap placed beneath the perforated double bottom of the vessel, and of course below the filter pad. The precipitated starch is further cleansed from acid by repeated washings and by pressure, until all trace of acidity has been eliminated, and the substance exhibits a neutral reaction. The next step is to treat the nitro-starch with a 5 per cent. solution of soda, in contact with which it is allowed to stand for at least twenty-four hours. The product is then ground up until a sort of "milk" or emulsion is obtained, and lastly treated with a solution of aniline, so that when pressed into cake, it contains about 33 per cent. of water, and 1 per cent. of aniline.

Dr Muhlhausen, working on these lines in the laboratory, prepared nitro- starch which contained 10.96 and 11.09 per cent. of nitrogen. When in the state of powder it is snow-white in colour; it becomes electrified when rubbed; it is very stable, and soluble even in the cold in nitro- glycerine. He has also prepared a tetra-nitro-starch containing 10.58 and 10.50 per cent. of nitrogen, by pouring water into a solution of starch in nitric acid which had stood for several days. The substance thus produced in the laboratory had all the properties of that prepared by the other process.