Elastic Gum, or Indian Rubber, is a substance of which a pretty full account has been given in the Encyclopedia. It has there been likewise observed how useful it might be, if we could form it into catheters and other flexible instruments, by dissolving it in a menstruum less expensive, or at least more easily attained, than ether. Since that article was published, we have seen an account of such a menstruum in the Annales de Chimie, by M. Geoffart (Chirly); and and of the expense of that menstruum, or the difficulty of procuring it, no complaint will be made, when it is known to be nothing more than very hot water.

The author was led to this discovery by some experiments made with ether on caoutchouc; of which he gives the following account:

"It appeared, even in my first experiments, that I was attempting too much, and giving myself useless trouble, in searching for a manner of completely dissolving the elastic gum, so that it might be again made up in new forms. I then thought that it would be easier to find out a method, as it were, of soldering it, and of not acting upon it more than might be necessary to cause its softened parts to reunite. Experience has shown me, that a strong pressure made upon two pieces of caoutchouc (when brought to that state of softness), and continued until they are entirely dry, causes them to contract so strongly an adhesion, that the piece, being pulled out till it broke, often broke, not at the united part, but by the side of it.

"By means of ether I immediately succeeded in making these tubes. The method which appears to me to succeed the best is, to cut a bottle circularly in a spiral flip of a few lines in breadth. It is very easy to cut a bottle in such a manner as to form a single long flip, and thus unnecessary joinings are avoided.

"The whole flip is to be plunged into ether, until it is sufficiently softened, which comes to pass sooner or later according to the quality of the vitriolic ether that is employed. Half an hour frequently suffices; but I have already observed, that there is a great diversity in the manner in which different sorts of vitriolic ether act, and of which the cause is not yet, so far as I know, determined.

"The flip being taken out, one of the extremities is to be taken hold of and rolled, first upon itself at the bottom of the tube, pressing it; then the rolling is to be continued, mounting spirally along the mould, and taking care to lay over and compress with the hand every edge, one against the other, so that there may not be any vacant space, and that all the edges may join exactly. The whole then is to be bound hard with a tape of an inch in width, taking care to turn it the same way with the flip of elastic gum. The tape is to be tied up with packthread, so that, by every turn of the packthread joining another, an equal pressure is given to every part; it is then left to dry, and the tube is made.

"The bandage is to be taken off with great care, that none of the outward surfaces, which may have been lodged within the hollows of the tape (of which the caoutchouc takes the exact impression), may be pulled away. I advise the application of a tape before packthread, because, especially in the thinner tubes, we should run the risk of cutting the caoutchouc, if the packthread were applied immediately upon it.

"It is easy to take off the tube of elastic gum which has been formed upon a solid mould of one piece; if the mould be made rather conic, it may be made to slide off by the smaller end; at the worst, it is easily accomplished by plunging it into hot water; for it is softened by the heat, and is distended; without this precaution it would be sometimes difficult to draw it off when dry, because, having been applied upon the mould whilst it had its volume augmented by the interposition of the ether, the parts of the caoutchouc are drawn nearer each other by the evaporation of the interposed bodies.

"The great affinity between these two bodies is seen by the length of time that the odour of the ether remains, notwithstanding the great volatility of the latter, and that the apparent dryness of the tube seems to show that there is none remaining; nevertheless, after a certain time, the odour disappears entirely. One of those tubes, which was made with ether after the method here described, does not retain the least trace of the solvent. It is needless to say, that it is easy to make tubes as thin or as thick as may be judged proper.

"Although the process that I am now describing is but very little expensive, yet I have tried to employ other solvents in lieu of ether, because it is not to be had in every place, and requires particular care in its preservation. I have employed, with some success, the essential oils of lavender and of turpentine; both of them speedily dilate the caoutchouc, and are of no great price. The disagreeable smell of the oil of turpentine becomes, perhaps, in process of time, less disagreeable than that of lavender. This last is dearer; but the difference is not so great as it appears at first; for we may make some advantage of the oil of lavender that is employed by the following operation: Upon plunging into alcohol the elastic tube prepared with the oil of lavender, the alcohol charges itself with the oil, and forms a very good lavender-water; the same as would be made by an immediate mixture of oil of lavender with spirit of wine. Immersion in this liquor also serves to hasten the drying of the caoutchouc instruments thus made by means of essential oils. I have made tubes with the oils of turpentine and of lavender; both are much slower in evaporating than ether. The oil of turpentine particularly appeared to me always to have a kind of stickiness, and I know not as yet that we have any means whereby to get speedily rid of its smell.

"Nevertheless there is a solvent which has not that inconvenience; it is cheaper, and may easily be procured by every one: this solvent is water. I conceive it will appear strange to mention water as a solvent of elastic gum, that liquid having been always supposed to have no action upon it. I myself refuted the idea; but reflecting that ether, by being saturated with water, is the better enabled to act on caoutchouc, and that this gum when plunged into boiling water becomes more transparent at the edges, I presumed that this effect was not due simply to the dilatation of its volume by the heat. I thought that, at that temperature, some action might take place, and that a long-continued ebullition might produce more sensible effects. I was not disappointed in my expectations, and one of those tubes was prepared without any other solvent than water and heat. I proceeded in the same manner as with ether: the elastic gum dilates but very little in boiling water; it becomes whitish, but recovers its colour again by drying it in the air and light. It is sufficiently prepared for use when it has been a quarter of an hour in boiling water; by this time its edges are sometimes transparent. It is to be turned spirally round the mould, in the manner we described before, and replunged frequently into the boiling water, during the time that is employed in forming the tube, to the end that the edges may be disposed. disposed to unite together. When the whole is bound with packthread, it is to be kept some hours in boiling water; after which it is to be dried, still keeping on the binding.

"If we wish to be more certain that the connection is perfect, the spiral may be doubled; but we must always avoid placing the exterior surfaces of the slips one upon the other, as those surfaces are the parts which most resist the action of solvents. This precaution is less necessary when ether is employed, on account of its great action upon the caoutchouc.

"It might be feared that the action of water upon caoutchouc would deprive us of the advantages which might otherwise be expected; but these fears will be removed, if we consider that the affinities differ according to the temperatures; that it is only at a very high temperature that water exercises any sensible action upon caoutchouc. I can affirm, that at 120° of Reaumur's thermometer (302° of Fahrenheit) this affinity is not such as that the water can give a liquid form to caoutchouc; and it does not appear that we have anything to fear in practice from a combination between these two bodies, which, though it really is a true solution, does not take place in any sensible degree but at a high temperature. It is therefore at present easy to make of caoutchouc whatever instruments it may be advantageous to have of a flexible, supple, and elastic substance, which is impermeable to water at the temperature of our atmosphere, and resists the action of acids as well as that of most other solvents. As to the durability of these instruments, few substances promise more than this, because it may be soldered afresh in a damaged part. Any woven substance may be covered with it; it is only required that the substance should be of a nature not to be acted upon during the preparation, either by ether or by boiling water; for these two agents are those which appear to me to merit the preference. Artists will frequently find an advantage in employing ether, as it requires less time; so that a person may make, in a single day, any tube he may have occasion for. The expense of ether is very little, since it is needful only to dispose the caoutchouc to adhere; and being brought into that state, the caoutchouc may be kept in a vessel perfectly well closed. It would also diminish the expense of the ether if, instead of washing it with a large quantity of water, there should be added to it only as much water as it can take up."