NO. IV The most powerful opponents with which gunpowder apparently has to contend, are nitro-glycerin and gun-cotton, and this on account of the extraordinary amount of power they possess; indeed, under certain conditions, they develop an almost irresistible force. But it is just this attribute of resistless violence, which has hitherto rendered them the most unsafe, the most dangerous compounds that can be applied to practical purposes. Man loses all control over these agents, inasmuch as an accidental blow or a slight concussion may nay, must produce a violent and perhaps most disastrous explosion. It is of no avail to possess a material which does several times the work of any other adapted for the same purpose, if life and property are in momentary danger of destruction. That this was one of the perilous conditions under which nitro-glycerin and gun-cotton were employed, is evidenced by numerous accidents which have occurred within the last few years in connection with their application to blasting purposes. But, both these dangerous agents have, within the last twelve months, been brought under control, and their action has been so modified that they may now be said to possess all the conditions necessary to constitute a safe and highly efficient material for blasting purposes. Taking them in the order to which they are referred to above, let us first examine the merits and demerits of nitro-glycerin which is one of the most remarkable materials employed to replace gunpowder as a destructive agent. This substance was discovered by Sobrero, in 1847, and is produced by adding glycerin, in successive small quantities, to a mixture of one volume of nitric acid of sp. gr. 1*43, and two volumes of sulphuric acid of sp. gr. 1*83. The acid is cooled artificially during the addition of glycerin, and the mixture is afterward poured into water, when an amber-colored oily fluid separates, which is insoluble in water, and possesses no odor, but has a sweet, pungent flavor, and is very poisonous, a minute quantity placed upon the tongue producing violent headache, which lasts for several hours. The liquid has a specific gravity of 1*6. and solidifies at about 5 Cent. (40 Fah.); if flame is applied, nitro-glycerin simply burns; and if placed upon paper or metal, and held over a source of heat, it explodes feebly after a short time, burning with a smoky flame, If paper, moistened with it, be sharply struck/a somewhat violent detonation is produced. In 1864, Mr. Alfred 3*Tobel, a [Swedish engineer, first attempted the application of nitro-glycerin as an explosive agent.. Some experiments were, in the first instance, made, with gunpowder, the grains of which had been saturated wi$i nitro-glycerin. This powder burnt much as usual, but with a brighter flame, in open air. When confined in shells orBlast-holes, greater effects were, however, produced with it than with ordinary gunpowder ; its destructive action is described as having been from three to six times greater than that of powder. The liquid could not be employed as a blasting agent in the ordinary manner, as the application of flame to it from a common fuse would not cause it to explode. But Mr. Nobel has succeeded, by employing a special description of fuse, in applying the liquid alone as a very powerful destructive agent. The charge of nitro-glycerin having been introduced, in a suitable case, into the blast-hole, a fuse, to the extremity of which is attached a small charge of gunpowder, is fixed immediately over the liquid. The concussion produced by the exploding powder, upon ignition of the fuse, effects the explosion of the nitro-glycerin. The destructive action of this material is estimated to be about ten times that of an equal weight of gunpowder, so that if we take 32,0001bs. as the average of work done by lib. of gunpowder, as stated in the early part of this paper, we get 328,3201bs., or about 146 tuns, as the work done by lib. of nitro-glycerin. Therefore, although its cost is about seven times that of Mast- ing powder, its use is attended with great economy, more especially in hard rocks, a considerable saving being effected by its means in the labor of the miners, and in the time occcpied in performing a given amount of work, as much fewer and smaller blast-holes are required than when gunpowder is employed. The material appears to have received considerable application in some parts of Germany and in Sweden ; but, in England, it has not progressed beyond the stage of experimental trials. Although nitro-glycerin appears to possess very important advantages over gunpowder as a blasting and destructive agent, the attempts to introduce it as a substitute for gunpowder, have been attended by most disastrous results, ascribable in part to some of its properties, and the evident instability of the commercial product. The explosion which occurred on board the West Indian Company's steamer European, will long be remembered by mauy. This distressing event happened on April 3,1866, when the European was unloading her cargo alongside the railway company's wharf at Aspinwall. The force of the explosion was such as to tear away the upper parts of the ship, and to blow the plates off her sides. The wharf, too, which was some 400ft. in length, was literally torn to pieces, and about fifty persons killed, while many others were seriously injured. By the ship's bill of lading a number of cases of nitro-glycerin were proved to have been on board, and doubtless careless handling of these packages, by men who were ignorant of the dangerous nature of their contents, led to the catastrophe. As if to impress the public still more strongly with the peril attending even the mere transport of#this destructive agent, another accident occurred on the 16th of the same month. Two oil-stained boxes, each measuring about 4 cubic fest, arrived at San Francisco by the Pacific mail steamer. They were removed from the ship into the city, in which they had no sooner been deposited than they exploded with a violence that shook the neighborhood like an earthquake, for a quarter of a mile around, and proved terribly fatal to human life. It was publicly stated that the boxes contained nitro-glycerin which was intended for sale to the mining companies in Nevada, Idaho, and Colorado. In Sydney, New South Wales, too, a tremendous explosion occurred on March 4,1866, in the stores of Messrs. Molison Black, in Bridge street, which were totally destroyed. The noise of the explosion is said to have very much resembled the discharge of artillery, while a column of the debris was thrown to a hight of about 150ft. A great amount of damage was done to the surrounding buildings, and property to a serious extent was destroyed. This explosion was traced to two packages of nitro-glycerin. There is yet another danger attending the substitution of nitro-glycerin for gunpowder in mining, and this relates to its manipulation when being prepared for firing a shot. Although the oil may have been safely transported to its destination, there is no guarantee that its destructive energy will not be developed before it is placed in the hole which is intended for it. Indeed, there are instances on record which show how slight a circumstance serves to spread death and destruction around, even in the handling of this material. It should be observed that among other disadvantages, nitro-glycerin freezes at a , somewhat high temperature, in which condition mere friction will explode it. A sad illustration of this fact occurred in 1867 at Hirschberg, in Silesia, where nitro-glycerin was being used in the boring of a railway tunnel. The oil was one day found to be frozen, and in this state was delicately handled, and fragments were detached by means of a piece of wood. In the bore holes the frozen nitro-glycerin exploded quite as well as the fluid. One day an overseer attempted to break up a lump of the frozen material with a pick. The result was a violent explosion of the whole mass, which caused the death of the incautious miner. Several accidents have also occurred in our own country since the introduction of nitro-glycerin, and many of those who were the first to experiment with it, have already given up its use. This material, therefore, was only worthy of utter condemnation for its fearfully dangerous and uncertain character, even under the most favorable circumstances. Its resistless energy is fully admitted, and its great value in this respect for mining operations duly recognized; but, inasmuch as it does not appear that there are any conditions under which it can be handled with safety, its use ought certainly to be everywhere prohibited.
This article was originally published with the title "Explosive Compounds for Engineering Purposes"