Compared with dynamite, it is not so violent, and occupies more space, weight for weight, and also requires a more complicated means of detonating it. On the other hand, gun-cotton is infinitely safer to store and manipulate, and is not so subject to detonation by concussion (not being so sensitive) as dynamite. _Fulminate of Mercury._--Fulminate of mercury is formed by the action of mercuric nitrate and nitric acid upon alcohol. The mode of preparation is as follows:-- Dissolve one part of mercury in twelve parts of nitric acid, and pour this solution into twelve parts of alcohol. Pour this mixture into a vessel which is placed in hot water until it darkens and becomes turbid and begins to evolve dense white fumes, then remove it from the water. The reaction goes on, with strong effervescence and copious evolution of dense white ethereal vapours. If red fumes appear, cold alcohol should be added to check the violence of the action. The operation should be performed at a distance from a fire or flame, and in a strong draught, so that the vapours may be carried off. When the liquid clears, and the dense white fumes are no longer given off, further action is stopped by filling up with cold water. The fulminate settles to the bottom of the vessel as a grey crystalline precipitate. The liquid is then poured off, and the fulminate washed several times by decantation or upon a filter. Dry fulminate of mercury explodes violently when heated to 367° F., when forcibly struck by the electric spark, &c. When wet it is inexplosive, and therefore it is always kept wet, being dried in small amounts when required for use. Fulminate of mercury is applied in many ways, either pure or mixed with other substances, as in percussion caps, percussion powder, primers, detonators, &c. For the purpose of detonating nitro-glycerine or its preparations, 15 grains of the fulminate are sufficient, but to detonate gun-cotton 25 grains are necessary. The fulminate in detonating fuzes should be enclosed in a copper case or cap, and must never be loose. The fulminate should be wet when charging the detonators, as it is very dangerous to handle when dry. Great care is requisite in handling this explosive compound. In addition to the foregoing explosive compounds and mixtures, the following explosive agents have also been employed for the purposes of submarine operations, though only to a small extent. _Dualin._--Dualin is a nitro-glycerine preparation formed by mixing sawdust and saltpetre with that substance. This preparation, inferior to dynamite, was employed by the Germans as the explosive agent for their submarine mines during the Franco-German war (1870-71). _Lithofracteur._--Lithofracteur is also a preparation of nitro-glycerine. It is composed of the following materials:--Nitro-glycerine, kieselguhr, coal, soda, saltpetre, and sulphur.