1074
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 17. KO. 10
The Decomposition of Liquid Hydrocyanic Acid’ By Mark Walker and D. N. Eldred THE PACIFIC R . & H CHEMICALC O R p , EI. MONTE,C.4LIF
During the past few years large quantities of liquid hydrocyanic acid containing 96 to 98 per cent HCN have been manufactured, transported over the public highways, and stored in warehouses, or specially constructed sheds, for indefinite periods of time. Numerous explosions have occurred in attempting to store the liquid confined in closed containers. Because of the high toxicity of the materials to nearly all forms of life, and the violence of the explosions, i t became increasingly important to determine the causes of these explosions. A study has been made of the behavior of liquid hydrocyanic acid, confined in steel bombs under controlled temperatures and pressures, alone and in the presence of catalysts and stabilizers. In this study, time-temperature and time-pressure curves and the character and composition of the products of the reaction have been determined. The explosions were found to result from the rupturing
of closed containers due to the formation of gases caused by the exothermic polymerization and decomposition of the liquid. Pressures of over 1000 pounds per square inch were frequently experienced. A t atmospheric temperature, polymerization without a sudden rise of pressure may result from the balance established between the heat of reaction due to decomposition and the loss of heat by radiation. The products of the reaction were (1) a solid black mass resembling willow charcoal or powdered carbon, which upon analysis proved to be a polymer of hydrocyanic acid slightly deficient in hydrogen and nitrogen, and (2) various gases among which ammonia and carbon monoxide predominate. Gaseous mixtures of hydrocyanic acid and air varying from 11 per cent to 60 per cent of HCN by weight, will explode when ignited. It is believed, however, that the explosions mentioned in this work do not belong to this class.
.. .... , EF2 states that, although absolutely pure hydrocyanic acid is an extraordinarily stable substance, the aqueous solution rapidly decomposes but the presence of a trace of mineral acid renders this solution more stable. Owing to occasional unexplained explosions dating back over a long period of years, liquid hydrocyanic acid has gradually acquired the reputation of being an unstable compound, while with its introduction into practical fumigation for various purposes these explosions have not only become more numerous but have been on a larger scale. It has been determined in this laboratory that gaseous mixtures of hydrocyanic acid and air may be made to explode when mixed in percentages by weight varying from 11to 60 per cent of HCX. The explosions mentioned above were, however, not of that nature, but were produced entirely by exothermic reactions occurring in the liquid within a closed container. As examples of the various occurrences the following instances are cited:
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I n 1861 Professor Campani, of the University of Siena, described a violent explosion that took place in his own laboratory. I n August, 1862, Professor Polacci3 observed a similar explosion. On March 8, 1918, in the laboratory of Mark Walker, in Los Angeles, Calif., a pint bottle containing liquid hydrocyanic acid exploded with a report like t h a t of a shot gun and threw fragments of glass and a cloud of black dust all over the room. On December 27, 1920, a 2.5-liter green glass bottle partially filled with liquid hydrocyanic acid exploded in the laboratory of The Pacific R. & H. Chemical Corporation, in Los Angeles, with a loud report, scattering glass and a black solid over a wide area. On May 22, 1918, at Perth Amboy, N. J., a drum containing liquid hydrocyanic acid blew up with a report that was heard over an area of several city blocks, the force of the explosion breaking about thirty-five window panes in a nearby building. I n July, 1921, an explosion of a drum of liquid hydrocyanic acid in Alhambra, Calif., caused the death of two horses, a number of chickens and pigeons, and rendered unconscious five men, while a boy nearly lost his life. 1 Received July 17, 1925. Presented as a part of the Symposium on Chemical Industries of the West a t the Joint Meeting of the Division of Industria! and Engineering Chemistry, Section of Paint and Varnish Chemistry, and Division of Cellulose Chemistry a t the 70th Meeting of the American Chemical Society, Los Angeles, Calif., August 3 to 8, 1925. 2 Ann., 187, 377 (1895). Salomone, Boll. chim.-farm., 6, 237 (1862).
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As very large quantities of an aqueous solution containing 95 to 98 per cent of hydrocyanic acid are now being used in the fumigation of citrus trees for controlling scale insects, as considerable quantities of this liquid are also being used for the extermination of vermin in ships, warehouses, and other places as well as for the fumigation of various articles of food, and as all this material is being transported over public highways with attendant risk, an investigation into the stability of the liquid seemed necessary. The purpose of this study was also to determine the nature of the causes that led to explosions and to see whether these explosions were due to the spontaneous rupture of the hydrocyanic acid molecule with the formation of a larger volume of other gases or simply to excessive gas pressure within the container. Previous qualitative experiments in this laboratory had shown that the introduction of hydroxyl ion into liquid hydrocyanic acid promptly started decomposition, which was primarily manifested by a yellow color in the liquid and subsequently by the deposition of a black solid, resembling powdered willow charcoal. It had been found a t the same time that sulfuric acid added in moderate concentration, as well as certain other stabilizing agents, retarded this change. These facts are in accord with the conclusions reached by various other investigators. Nef2 states: “If the acid contains traces of impurity such as water or potassium cyanide it rapidly turns brown, forming the so-called azulmic compounds, about which very little is known. The aqueous solution rapidly decomposes, especially if exposed to the light, forming a brown precipitate of azulmic acid, while ammonia, formic and oxalic acids, and other substances remain in solution.” Richter,4 in addition to the above, mentions the formation of white crystals soluble in ether and having the same percentage composition as hydrocyanic acid, which break down on boiling into glycocoll, carbon dioxide, and ammonia, which decompose a t 180’ C. with explosion and partial reformation of hydrocyanic acid. Prior to the investigations described herein, the writers had determined that when liquid hydrocyanic acid was heated in a sealed container the liquid changed completely into a 4
3rd American Edition, 1918, Vol, I, p. 229.
solid black substani:e, atid frequeiitly this chniige WdY accompanied by a sudden rise of temperature and pressure. On the basis of these facts, plans xere made to study t,he behavior of liquid hydrocyanic acid alone, as well as in the preser~ccof catalysts and of stabilizers, when aibjeatrd to heat a.nd pressure in a sealed vessel, noting t,he e1a.psed time before active dewimposition began, t,lie rise of temperat,rlre aud of pressure during the a h v e periiid, as well as the diarneter arid co~nposit,ionof tlie prodiict,s of t,lie reaction. Inasmuch as at ordinary atmimplicric t,emperatiire it hail Gcen foimd that the leiigtli of the primnry reaction period w a s imeerbain, as well tis frcr~ueut,lyext~remelplong. it, was decided to ucoeierate the renotirin til- means of externally ripplied heat., t h u s c c r ~ n o m k i ~ill~ gtime. Procedure A fixed quantity (2.50 cc.) of pure liquid hydrocyanic acid was coiiiined in a steel boinb and ~:iintinuous, definite pressure, produced by heat f r m a gas iiame applied to tlie exterior uf the bolnb, was maintuined till a sudden rise of the pressure indicated that what may be termed the “recomlary” reaction period had commenced. At this point t,lie gas &me was immediately shut off, t.he elapsed time, in hours, was tinted, and frequrnt readings of temperature and pressure were taken while the pressure rose to, and definitely rercdcd from, a maximimr. Experinients ~ ~ i tliquid l i Iiydroeyaiiic acid aloiie were made in whieli the initial pressure was maintained at 50, 75, 100, 160, and 2(w) pounds per q u a r e inch. These experiments were followed by others in which liquid hydrocyanic acid stabilized with ccrtaiii reagents was used, throughout the same pressure range, and these ill turn were followed by experiments iii which the liquid liydrocyanic acid was catalyzed by suitable compounrls.
Plate I-Romb
Disasaemhled
111 many cases aft.er the reaction had ended, and the bomb iiad c!ooled to atmospheric temperature, the gases were withdrawn and analyzed. The solid material was then removed and stored for future analysis, while t.lre bomb was cleaned, retinned if necessary, and put back into service.
thimble was carefully smoothed off and was tapered slightly on the outer edge. When in use t.he thimble was held in a vert,iral position between two solid iron flanges, 25 mm. (1 inch) thick by 16.5 mm. inches) diameter, having seven equally spaced 15-mm. (5/&x:h) holes for the rei!eptioii of 13-mm. (‘/riuch) M t s around thcir circumferences. In scaliny t.he bomb, a soft copper ring was laid between the upper edge of the thimble and the Iowcr sidc of the top plat.e, after which the iiuts on t,hr bolts were screwed down, thus making 11 gasiiglrt joint. Tilo iroii cover tiad t i centrally l o c a t e d liclle threaded for a 6mm. (l/
