Egyptians used it, consciously or otherwise, as they evidently obtained nitric acid from their saltpetre, and this must have in their experiments been mixed with common salt, thus giving nitrous gases and chlorine. In a Danish receipt, not much after the time of the discovery of this gas, acid fumigation is recommended, the fumes to be obtained by pouring sulphur or nitric acid or common salt. The first gives muriatic acid only, the second chlorine as stated.

Chlorine decomposes readily salts of ammonia, thus destroying manures, and this power is peculiarly shown by chloride of lime, and other of its alkaline compounds. At the same time a peculiarly pungent gas is given off. It cannot, therefore, be well to use it much with manures. When it unites with lime it forms ultimately chloride of calcium, a very deliquescent body. It ought never, therefore, to be mixed with lime-wash.

It is made by pouring muriatic acid on peroxide of manganese. It is also made to flow very quietly by adding one and a quarter of alum cake or sulphate of aluminum, or potash alum to one of chloride of lime; also, as Mr. Stone recommends, by dropping occasionally a crystal of chlorate of potash into muriatic acid. When vile smells are to be destroyed nothing is superior to chlorine. The action is double: the chlorine combines with hydrogen and thus forms new compounds, but it also, as with water, renders oxygen nascent, so that it is a powerful oxidizing agent, and so oxygen, with which we at first began, again comes forward.

In fumigating, we find the senses to be the best judges; there ought to be in the air enough gas to give a very faint smell at most. As a preventive in common cases, it is enough if the smell is so slight that it is perceived only after coming from the open air. Nothing destroys liquid and solid putrid matter more rapidly than chloride of lime.

Muriatic and Nitric Acids.-Guyton Morveau in 1773 recommended muriatic acid as a disinfectant. This may be called the beginning of acid fumigation, not forgetting the ancient use of vinegar, and the pretty well known action of acids. The muriatic acid was made simply by pouring sulphuric acid on common salt. It is powerful, and the proposer has written an octavo volume on it of much interest; but even he gave preference to chlorine, which Fourcroy introduced as a fumigating agent in 1791. Guyton Morveau was much aggrieved when Dr. Carmichael Smith used nitrous acid at Winchester in 1780, and afterwards received a reward of five thousand pounds from Parliament in 1802. He was glad to find that even in England men did him justice as the author of acid fumigation. It is interesting to see how men ad

mire the less valuable first. Nitrous fumes are powerful disinfectants, but can never be used without great danger where there are living beings. We have heard lately of three deaths by exposure to these gases, even when they did not act powerfully on the senses. They are destructive, like chlorine in all bad cases, but there do not appear to be cases where they are to be preferred. The safest use of nitric acid is in the form of nitrate of potash, where we know it preserves, or in the mode which received the recommendation of the Academy of Dijon in 1767. We suppose that when they used it in ventilation the saltpetre was heated, in which case it would give off oxygen gas, which at first is very pure; afterwards nitrogen comes off, and the salt itself, or at least the base, is carried into the air, causing a very stifling sensation. The oxygen, however, would be valuable, and this plan might receive more attention. It is remarkable as having been tried before the discovery of oxygen, which was in 1774. When we can keep up a constant stream of pure oxygen, active or less so, by a self-acting process, we shall gain some new results.

Heat and Cold.-The gases spoken of as oxygen, sulphurous acid, chlorine, and nitrous gas, are all destructive. Even muriatic acid is so to a considerable extent. They may be used to purify the air, because they diffuse into it, and leave no corner of the apartment untouched. All these disinfect by destruction. There is a class of agents which disinfects by preservation, if we may be allowed to speak so. These may be called antiseptics. Boyle, who separated chemistry from alchemy, began the modern examination of these bodies, and showed the influence of heat and of cold. Cold prevents the motion of particles: bodies greatly cooled cannot decay because the parts when cold have no locomotion. Like a regiment frozen in snow, they stand under the most powerful arrest. The influence has been lately called colytic, from the Greek word kwλów, to restrain. Animal matter seems capable of being preserved to endless time by cold: witness the frozen elephants or mammoths of Northern Asia. They have probably remained for ages, and why should they change? The cold removes putrid matter out of the air. Dr. Southwood Smith obtained a putrid organic liquid from the atmosphere of an unclean place, by passing it through a tube artificially cooled. Guntz put a bell-jar over putrid matter, and cooled it suddenly, when he obtained drops of a putrid liquid. Cold removes vapour, and with it matters which remain suspended with it. No wonder, then, that cold should prevent some diseases. Cholera evidently avoids it. Cold acts also by preventing putrefaction even when the particles are not arrested by freezing.

In all our thermometers we find temperate marked at 55° Fahrenheit (18 Cent.) A gentleman of our acquaintance always puts on a great-coat when the thermometer is under 56°. This is from independent experience. Putrefaction has been found. to diminish to a mere trifle at 54°, or close to it. Above that the gases begin to arise. For this reason a place which is healthy at 53° may become unhealthy at 55°, and most persons will not remark the change of temperature. It is strange that this point in putrefying liquids should be, we may say, quite the same as the feeling of cold in the living body.

We must be thankful if in any district ill provided with means of purification, we have less than 54° of heat. Much of the health of this country must be owing to this condition being found in it. Marshy or undrained lands become cold and sour or peaty, and disinfect themselves. In warm countries marshes are much more dangerous, and there we find cold an infecting agent. The night comes, and condenses, like the belljar spoken of, and liquids with poison in solution fall down as mist. Sometimes we find a little hollow of a field or county filled with this vapour when the plain is free. If any one ventures there he may be injured even if he be only a few feet lower than his companions. We hear in hot countries of men who even receive no injury standing, but suffer the fevers and ague of the district if they lie down. This is an action of cold. The Innuit builds his house of snow, and has only a small hole in it; he cooks and burns fat there, but we never hear of fevers and agues from putrefactive matter. The cold no doubt condenses it at once against the ice walls. Rain washes the air in a similar way, and cold and wet certainly produce pure air. If they exist in a country with good drainage and little organic matter, they produce some of the most important conditions of health.

If we do not utter contradictions, we become one-sided; nature to us is full of them. Heat, like cold, is a source of health, and has a disinfecting power. In some cases it is colytic. When the Damaras cut meat into strips and dry it in the sun, the decay is arrested by an act resembling freezing. Dr. Henry showed that even if the poison of disease were contained in substances, it was destroyed by heat. Vaccine matter lost its power at 140° F., the heat being continued for three hours. At 120° three hours did not destroy it. This corresponds with the temperature of coagulation. At this point something peculiar happens to animal matter, and amongst others it becomes cooked. Dr. Henry found it needful to heat the clothes of fever patients to 200° F. in order to produce disinfection.

Heat expands bodies, and when the fever matter is condensed

VOL. XLIV.NO. LXXXVIII.

2 H

over a marshy region, the sun raises the vapour, and it is diluted to such an extent as to become innocent. Cattle-plague does not appear to be diluted in this way, so as to become innocent. Why should heat be called a disinfectant if it promotes putrefaction? It promotes putrefaction and its consequences, especially between 54° and 140°, but this must be in the presence of water. If it is dry heat, it arrests at all temperatures. Even if moisture be present, the disinfecting action is powerful, perhaps all-powerful, if the temperature of 140° be continued long; but, as Dr. Henry and others have shown, it is not complete if that point is kept up a short time only. So also for the destruction of dangerous ingredients, in heat we have this point of disinfection, although recent inquiries seem to show that to destroy trichinæ and similar enormities it is well to go higher.

The action of heat and moisture in producing putrefaction is by facilitating motion, and first the motion of organic substances or compound bodies. When the heat is great these bodies either lose that union with water, in which only they can act in living organisms, or are otherwise removed into the sphere of inorganic chemistry. Chemistry changes; that is, substances act differently, according to temperature. The chemistry of human life goes on between 95° and 100° F.; we resist attempts to raise us above or below this point. The relations of man to nature change with every change of the thermometer, and in every climate a new relation of animal and vegetable life is found. The temperature of the air for man must be between 40° and 100°, although we may endure a little more or less with great inconvenience. All chemical actions differ as the thermometer rises or falls, until blood refuses to take up oxygen, and at last, in enormous heats, even hydrogen and oxygen, which we now find combining with violence, would refuse to acknowledge each other.

Carbolic Acid.-Heat is compound in its action, cold is purely colytic. There is another action of pure colysis, so far as we know, in carbolic acid. We feel inclined to go back to the ancients, when speaking of this substance. The Egyptians, as we find in Hoefer's History of Chemistry, used oil of cedar, which he calls turpentine. We are inclined to think that it was not true turpentine, which is not a very good agent in embalming, and we think rather that it was a very mixed tar-oil, and would contain the tar acids. Ancient Egypt wrote little for us, but we find in Pliny such an account of the manufacture of oils as a literary man would write. The tar was boiled, and the fleeces of sheep held over it, in order to collect the less volatile oils. The naphthas, by this process, would be lost. The distillation must have been carried very far, as there was obtained a reddish

pitch, very clammy, and much fatter than other pitch. This was the anthracene, chrysene, and pyrene of later times.

The remainder was the palimpissa, or second pitch,-what we call pitch, as distinguished from tar. Sometimes this name was given to the substance obtained by distillation; a good deal of confusion, therefore, is caused. The product in the fleece would contain the heavy oils, and with them the carbolic acid (phenic acid, or alcohol). It was called picenum, or pissenum, or pisselæum; that is, pitch or tar oil, as we call the crude product now. They used it for toothache, as we use it still, and for skin diseases of cattle, which we are beginning to do also. Hams were also smoked by hanging them on the roof, above the fires.1

Runge called the kreosote from coal, carbolic acid, or coal-oil. It really has acid properties, but its composition is analogous to alcohols; and it is strange that several bodies of that constitution should have so much power of preventing putrefaction. Reichenbach obtained it among his many new bodies, which people could not find till long after he did. Alcohol, common methylated spirit, fusel oil, carbolic acid, and cresylic acid, which latter is found in the distillation from coals, are all antiseptic. Carbolic acid is found in the products of distillation of wood, of benzoin resin used in fumigation. It is even found, according to some, in animal secretions. The tar-barrels burnt in the time of epidemics, from the earliest date till this year, give out this acid, but would give out more if the flame were suppressed, and distillation only allowed. The world has admired this substance without knowing its existence, and sought it in every corner, using various names to express it, wrapping it in bundles to carry around them, burning it in pastilles for fumigation, and sometimes in public in great bonfires. Savages use petroleum for their wounds and their cattle, and the most civilized of old times kept in products of tar the dead that they desired to preserve to a joyful rising. Bishop Berkeley tells us that it was used as tar-water in America, the tar being merely stirred up with the water, and the water drunk, a glass at a time. He himself had tried it in many diseases, and tells us of small-pox, erysipelas, skin diseases, and ulcers, being cured by it; quotes the pitching of wines by the Romans as a proof of its value, and Jonstonus, in his Dendrographia, as saying that it is wholesome to walk in groves of pine-trees, which impregnate the air with balsamic particles. The learned writer then goes on to say that, although he may be ridiculed, he suspects tar-water is a panacea; and as the old philosopher cried aloud from the house-tops to his fellow-citizens, "Educate your children;" so I confess, if I 1 This and other allusions from Lecture on Disinfection, Society of Arts Journal, 1857.