PREPARATION OF MATERIALS.
THIS remarkable substance was first brought to the notice of the scientific world by Schonbein*, who obtained in this country a patent for his invention.
Its applicability as an explosive substance does not appear to have realized the expectations of its promoters, and little is now heard of it as a substitute for gunpowder.
It appears that the explosive properties of ligneous substances when submitted to the action of nitric acid, was known some time previous to the introduction of gun-cotton by Schonbein.
The Photographer, however, applies this substance to a more peaceful, and, I should hope, a more useful purpose than that contemplated by its inventor.
Gun-cotton is formed when carded cotton, flax, or any other form of woody fibre, is submitted to the action of nitric acid; it is, in fact, a combination of wood-fibre with a certain proportion of the nitrogen of the acid. In order that this combination may take place, the nitric acid must be in what is called the nascent state, free to combine. For this purpose, a mixture of sulphuric acid and nitrate of potassium, or sulphuric acid and nitric acid, are mixed in certain proportions. The nitrate of potassium, or nitric acid, is immediately decomposed by the sulphuric acid, giving rise to the formation of nitric acid vapour, which at the moment of its formation combines in certain proportions with the cotton fibre, producing thereby the explosive substance called gun-cotton.
It appears that gun-cotton is composed of two distinct, though analogous substances; one is called pyroxylin, leaves no residue on explosion, and is not soluble in ether, the other zyloidin, leaves a residue on explosion, and is soluble in ether.
The latter substance is produced by the action of the strongest nitric acid on starch or gum, which dissolves them into a thick mucilaginous liquid, precipitated by water, soluble in alcohol, and very soluble in glacial acetic acid; it in fact forms, with acetic acid, a hard and beautifully transparent varnish.
I have used this solution as a vehicle for holding the iodide of potassium, when endeavouring to form a sensitive medium on glass. It answered to a degree. It was one of my earliest experiments, but was abandoned for collodion.
It may be remarked, that collodion cannot be made with zyloidine alone; it forms no coherent film when dried on glass from its solution in ether, consequently it is a misnomer to call iodized collodion zyloiodide of silver, when the zyloidine it contains is only one of its component parts.
I shall give several receipts for making gun-cotton, from either of which a good dissolving cotton may be obtained. Many methods have been given, but I should only be confusing the subject to attempt to give the whole; and it would be foreign to the limited purpose of this work to do so.
The results, however, in regard to the solubility of the product vary so much with the strength and proportion of the acids used, as to render it extremely difficult to name any one mode in particular which would entirely succeed under all circumstances. In all cases it will be found more easy to prepare a cotton which will explode readily, and yet be only partially soluble, than one which will entirely dissolve in sulphuric ether.
Nitre, in powder, dry.
The nitre, sulphuric acid, and cotton, are weighed in the above proportions, and placed near at hand within reach of the operator, to prevent delay in mixing when the operation has commenced. First, put the powdered nitre into a basin placed firmly, so that there shall be no fear of its upsetting, then pour the proportion of sulphuric acid on the powdered nitre, stirring them well together with a strong glass rod for a few seconds.
Immediately the two are mixed add the cotton, having previously pulled out the fibres, and mix them well together with two glass rods, in order that the whole of the cotton may come in contact with the nitric acid vapour, which is being rapidly formed from the mixture. This action must be continued for about two minutes, then remove the cotton quickly from the basin with the glass rods, and plunge it into a large quantity of water; it must be well washed in repeated changes of water, until all the acid and nitre are washed away.
The cotton is then collected together, and first pressed between the hands to drain off the water, and then still further dried by pressure in a cloth ; the fibres of cotton can now be carefully separated, and hung up with pins to the edge of a shelf, or any other convenient place, to dry. There is no necessity to use artificial heat, as the small quantity requisite for a few ounces of solution can easily be dried without it.
It is necessary that this operation should be conducted either in the open air, or in some convenient situation where there is sufficient draught to carry off the nitric acid vapour generated.
The next receipt is by certain proportions of nitric and sulphuric acids.
Nitric acid Sp.G. 1.4500
1 oz. by measure
Sulphuric acid, ordinary.
1 oz. ,,
80 grs. by weight
The fibres of cotton must be well separated, as in the preceding mode. The two acids are first mixed, the requisite proportion of cotton added as quickly as possible, and well stirred with the aid of two glass rods until the cotton is thoroughly saturated. The cotton may remain ten minutes, or even longer, in contact with the acids,; it is then removed, and plunged into water to undergo the same washings, &c., as in the former recipe.
Water must not be spared in washing the cotton, for not a trace of acid should be left; the collodion would be injured by any remaining.
Or the following:
1/2 oz. by measure
Nitric acid Sp.G. 1.4500
1/2 oz. ,,
1 oz. ,,
Sulphuric acid, ordinary
The two first acids are mixed, and the sulphuric acid added afterwards. The manipulation is the same as with the preceding formula.
A soluble cotton cannot be prepared with the strongest nitric and sulphuric acids, but a most explosive gun-cotton is obtained. This shows that a certain proportion of water is necessary to produce a soluble gun-cotton.
When, therefore, an explosive but insoluble cotton is the result of the operation, it may be taken as a sure indication that the acids have been used too strong, and require dilution. If, however, the product is neither explosive nor soluble, it shows that the mixed acids have been too weak, and unable to produce the requisite change. The remedy, therefore, in the latter case, lies the other way.
It is only by experiment that the proper strength of the acids can be ascertained with precision.
If, therefore, it is not shown with certainty the result likely to be obtained by a mixture of the two acids, a small quantity of each, equal volumes for instance, should be mixed, and a portion of cotton added, the immersion being continued for three or four minutes; after washing and drying the cotton, test its solubility in ether; if it should be found entirely insoluble, but very explosive, make a fresh mixture, adding for trial a quantity of water a quarter of the bulk of the mixed acids ; add the water to the sulphuric acid first, then the nitric acid.
Immerse a small quantity of cotton for the same time as in the previous experiment, and if, after washing and drying, the cotton is found to be insoluble, and not explosive, it may be taken as an indication that too much water has been added. Having got these two data, giving the two extremes, little difficulty will be experienced in getting at the right proportion for the third trial.
For the first trial, take
For the second trial, take
The above is the surest way that can be given for testing the two acids to ascertain if they will, when mixed, produce a soluble gun-cotton.
I can see no advantage in using paper for making a soluble substance. An excellent collodion can be made with lint, and also with fine Swedish filtering paper; but the advantages, if any, do not in any way counterbalance the increased expense of the materials.
*Christian Frederick Schonbein, Born at Metringen, Germany, 18th October 1799
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