PRUSSIC ACID, Medical Properties of. This is termed also, from its chemical composition, hydrocyanic acid. Its medical employment, and its connection with medical jurisprudence, from the frequent use of it in cases of death, accidental or intentional, merit the most atten tive consideration. But these are unsuited for popular discussion. A few important rules and cautions can alone be furnished here.
Much variation in strength exists in the acid (that is, the dilute acid, for the anhydrous is always of definite strength), owing to differ ent methods of preparation. Thus not only does a difference of strength exist in the acid as it is enjoined to be prepared by the Edinburgh and London colleges, hut even in England two preparations are commonly met with, that enjoined by the London Pharmaeopceia, which contains 2 per cent. of real acid, and that which has been long known as containing 4 per cent. The substitution of the one for the other in preparing a prescription might lead to serious if not fatal consequences. This anomaly will bo removed by the General Pharmacopeia now preparing for use through all Great Britain and Ireland. A still greater difference exists in the strength of the pre parations met with in different countries of the Continent. No one in travelling should ever prescribe prussic acid, unless he has previously ascertained what preparation will be employed in compounding the prescription.
As it undergoes decomposition by time, especially' if exposed to the light, and is readily volatilised at a high temperature, it should be kept in the dark, and in a cool place. As it is specifically lighter than water, it rises to the surface in watery fluids. The fluid in which it is kept should be well shaken before pouring it out. When employed externally as a lotion, in which case it is used in larger doses than when meant for internal employment, great care should be observed to distinguish it. lest it should be accidentally taken internally. This is attempted to be accomplished by using phials of a peculiar shape and colour. Even its external employment demands great care, for when the cuticle is abraded or cracked, it is readily absorbed, and may prove fatal. The cuticle, even when in a state of integrity, is not proof against the vapour of prussic acid. All bottles containing the acid should be kept well corked, as the vapour is the most potent form which can influence the human frame. It is important to know that this acid is liable to be formed in some medical mixtures spon taneously, without the assistance of beat or distillation. Thus it has been formed in a mixture of carbonate of potash with tincture of hyoseyamus, doubtless by the decomposition of the hyoseyamid furnishing nitrogen (see 'Journ. Pharm. Soo.; vol. xiii. p. 632).
When first introduced into medical practice, high expectations were formed of the utility of prussic acid. Subsequent experience has moderated these expectations ; but there is no doubt that it might be found useful in many instances where it is not employed, the dread of accidents deterring many medical men from using it. Such hesitation
displayed by those who know its properties should furnish a salutary caution to all persons against employing it on their own responsibility. The diseases in which it has been most recommended are—affections of the lungs, whether acute inflammation,! after the active stage is passed, or those of irritation. Among the former, booping-cough is unquestionably benefited by it. But here great caution is necessary. Its premature employment, by checking the cough, induces inflamma tion, often of a very alarming kind. The dose should at first be very small, and most slowly increased. In some works, even emanating from medical men, large doses are most culpably ordered. More relief is obtained in consumption from Conium than from this acid. Some affections of the stomach receive signal relief; others derive not the least benefit from it. The explanation of this appears to be that in the former the causes of the disorder, as well as its seat, are in the stomach itself; while in the latter the pain is felt chiefly in the stomach, but the cause is in the spinal chord. Treatment directed to the spine will in general quickly and often permanently relieve the sufferer. (Teale's 'Treatise on Neuralgic Diseases.') Cutaneous diseases are alleviated by lotions and ointments containing hydro cyanic acid. But the cautions above given must be carefully observed during their employment.
The most useful hints which can be here given relate to the treat ment of poisoning by prussic acid. So soon as it is ascertained or suspected that any one has taken an over or poisonous dose, cold water should be dashed over the head and back. The vapour of ammonia (common smelling salts) or of chlorine should be applied to the nostrils ; or very dilute liquor ammonite may be thrown into the stomach. While these things are doing, other persons may prepare a weak solution of carbonate of potash (common pearlashce will answer); and some sulphate of iron (copperas) is to he dissolved in a large quantity of water. Some of the solution of the carbonate of potash is to be given to the patient, followed immediately by some of the solution of copperas. Phials containing these two solutions might be kept ready prepared in chemists' shops, so as to be at hand instantly. This if done promptly, will save the patient. Artificial respiration, if speedily resorted to, is useful, as is likewise bleeding from the jugular vein. Prussic acid (or its elements, which easily act on each other so as to form this compound,) exists in the leaves of the Cerasus lauro-cerasus, or Cherry-laurel, the mere bruising of which developer the characteristic odour and effects. This shrub is unfortunately often confounded with the true Bay, or Caesar's Laurel, by cooks and confectioners, who use these leaves, (the amount of oil, from difference in the amount of the elements, varies at different periods of the year), to flavour dishes and cheese-cakes, with often fatal effects. Bitter almonds develope prussic acid.