C:NO
|| Hg.
C:NO
They are very generally regarded as iso-nitroso compounds.
The principal compound of fulminic acid is the mercury salt commonly known as fulminating mercury. It is prepared by dissolving mercury in nitric acid, and then adding alcohol to the solution, 1 part of mercury and 12 parts of nitric acid of specific gravity 1.36, and 5-1/2 parts of 90 per cent. alcohol being used. As soon as the mixture is in violent reaction, 6 parts more of alcohol are added slowly to moderate the action. At first the mixture blackens from the separation of mercury, but this soon vanishes, and is succeeded by crystalline flocks of mercury fulminate which fall to the bottom of the vessel. During the reaction, large quantities of volatile oxidation products of alcohol, such as aldehyde, ethylic nitrate, &c., are evolved from the boiling liquid, whilst others, such as glycollic acid, remain in solution. The mercury fulminate is then crystallised from hot water. It forms white silky, delicate needles, which are with difficulty soluble in cold water. In the dry state it is extremely explosive, detonating on heating, or by friction or percussion, as also on contact with concentrated sulphuric acid. The reaction that takes place upon its decomposition is as follows:—
C_{2}N_{2}O_{2}Hg = Hg + 2CO + N_{2} (284)
According to this equation 1 grm. of the fulminate should yield 235.8 c.c. (= 66.96 litres for 284 grms.). Berthelot and Vicille have obtained a yield of 234.2 c.c., equal to 66.7 litres for one equivalent 284 grms.
Dry fulminate explodes violently when struck, compressed, or touched with sulphuric acid, or as an incandescent body. If heated slowly, it explodes at 152° C., or if heated rapidly, at 187° C. It is often used mixed with potassium chlorate in detonators. The reaction which takes place in this case is 3C_{2}N_{2}O_{2}Hg + 2KClO_{3} = 3Hg + 6CO_{2} + 3N_{2} + 2KCl.
On adding copper or zinc to a hot saturated solution of the salt, fulminate of copper or zinc is formed. The copper salt forms highly explosive green crystals. There is also a double fulminate of copper of ammonia, and of copper and potassium. Silver fulminite, C_{2}N_{2}O_{2}Ag_{2}, is prepared in a similar manner to the mercury salt. It separates in fine white needles, which dissolve in 36 parts of boiling water, and are with difficulty soluble in cold water. At above 100° C., or on the weakest blow, it explodes with fearful violence. Even when covered with water it is more sensitive than the mercury salt. It forms a very sensitive double salt with ammonia and several other metals. With hydrogen it forms the acid fulminate of silver. It is used in crackers and bon-bons, and other toy fireworks, in minute quantities. Gay Lussac found it to be composed as follows:—Carbon, 7.92 per cent.; nitrogen, 9.24 per cent.; silver, 72.19 per cent.; oxygen, 10.65 per cent.; and he assigned to it the formula, C_{2}N_{2}Ag_{2}O_{2}. Laurent and Gerhardt give it the formula, C_{2}N(NO_{2})Ag_{2}, and thus suppose it to contain nitryl, NO_{2}.
On adding potassium chloride to a boiling solution of argentic fulminate, as long as a precipitate of argentic chloride forms, there is obtained on evaporation brilliant white plates, of a very explosive nature, of potassic argentic fulminate, C(NO_{2})KAg.CN, from whose aqueous solution nitric acid precipitates a white powder of hydric argentic fulminate, C(NO_{2})HAg.CN. All attempts to prepare fulminic acid, or nitro-aceto- nitrile, C(NO_{2})H_{2}CN, from the fulminates have failed. There is a fulminate of gold, which is a violently explosive buff precipitate, formed when ammonia is added to ter-chloride of gold, and fulminate of platinum, a black precipitate formed by the addition of ammonia to a solution of oxide platinum, in dilute sulphuric acid.
Fulminating silver is a compound obtained by the action of ammonia on oxide of silver. It is a very violent explosive. Pure mercury fulminate may be kept an indefinite length of time. Water does not affect it. It explodes at 187° C., and on contact with an ignited body. It is very sensitive to shock and friction, even that of wood upon wood. It is used for discharging bullets in saloon rifles. Its inflammation is so sudden that it scatters black powder on which it is placed without igniting it, but it is sufficient to place it in an envelope, however weak, for ignition to take place, and the more resisting the envelope the more violent is the shock, a circumstance that plays an important part in caps and detonators. The presence of 30 per cent. of water prevents decomposition, 10 per cent. prevents explosion. This is, however, only true for small quantities, and does not apply to silver fulminate, which explodes under water by friction. Moist fulminates slowly decompose on contact with the oxidisable metals. The (reduced) volume of gases obtained from 1 kilo. is according to Berthelot, 235.6 litres. The equation of its decomposition is C_{2}HgN_{2}O_{2} = 2CO + N_{2} + Hg.
Fulminate of mercury is manufactured upon the large scale by two methods. One of these, commonly known as the German method, is conducted as follows:—One part of mercury is dissolved in 12 parts of nitric acid of a specific gravity of 1.375, and to this solution 16.5 parts of absolute alcohol are added by degrees, and heat is then slowly applied to the mixture until the dense fumes first formed have disappeared, and when the action has become more violent some more alcohol is added, equal in volume to that which has already been added. This is added very gradually. The product obtained, which is mercury fulminate, is 112 per cent. of the mercury employed. Another method is to dissolve 10 parts of mercury in 100 parts of nitric acid of a gravity of 1.4, and when the solution has reached a temperature of 54° C, to pour it slowly through a glass funnel into 83 parts of alcohol. When the effervescence ceases, it is filtered through paper filters, washed, and dried over hot water, at a temperature not exceeding 100° C. The fulminate is then carefully packed in paper boxes, or in corked bottles. The product obtained by this process is 130 per cent. of the mercury taken. This process is the safest, and at the same time the cheapest. Fulminate should be kept, if possible, in a damp state. Commercial fulminate is often adulterated with chlorate of potash.