DR. W. SIMON ON LIQUID AIR. Of all the pleasing events on the programme for the A. Ph. A. visitors at Balti more, August 29 to September 6, not one attracted the universal attention given the lecture on Liquid Air by Dr. Wm. Simon. The professor spoke without notes, but the following is a stenographic view of the lecture. It was given in the happy vein and practical manner peculiar to this popular demonstrator: DR. WM. SIMON. It is Now Thirty Years since I had the pleasure of taking a carriage drive between the two German University-towns, Giessen and Marburg. On this memorable trip I had the honor to act as the escort of a small iron flask containing two pounds of liquefied carbon dioxide. I am inclined to think that this transport of a liquefied gas was one of the first, if not the first one, ever made. I was at that time assistant to Professor H. Will of Giessen, who was so fortunate as to have the necessary outfit for the liquefaction of the gas, while his colleague in Marburg had no such apparatus, but desired to show to his class the wonderful substance-liquefied carbon dioxide. The reason why the railroad could not be used for transporting the article was due to the most positive refusal of the railroad authorities to ship so dangerous, so explosive, an article as liquid carbon dioxide was believed to be. Thirty years have passed since that time and to-day liquefied gases such as ammonia, carbon dioxide and others are manufactured in quantities of hundreds of tons and are taken as freight by transportation companies all over the world. Civilization has known great changes since small quantities of liquid chlorine, ammonia and other easily liquefiable gases were obtained for the first time by Faraday in 1826. Most of the Conditions on which depend the conversion of gases into liquids or solids have long been known, and I need scarcely mention that lowering of temperature and increase of pressure are the two conditions essential to accomplish this result. Yet it is within the memory of perhaps all of us that a number of gases, such as the two chief constituents of air, as well as carbon monoxide, and methane were looked upon as permanent or stable gases. They were believed to be so because all attempts to liquefy them had utterly failed, notwithstanding that they had been subjected to an enormous pressure. It Was Not Until it Was Fully Understood, as first shown by Dr. Andrews, of Scotland, in 1869, that pressure alone, or at least pressure at an insufficiently low temperature, can never change the gaseous condition of these substances. In other words, it was found that there exists for every gas what is known to-day as its critical temperature, i. e., the temperature above which the application of pressure, no matter how great, will not bring about liquefaction. This fact being recognized, the problem of liquefying the then called permanent gases was once more attacked and practically solved in 1877 almost simultaneously by Cailletet in France and Pictet in Geneva. Unfortunately we have no time to cousider the construction of the various sorts of apparatus used at different times for the liquefaction of gases; suffice it to say that in all the modern appliances the required low temperature is obtained by the expansion of a previously compressed gas; and here permit me to remind you that a change of volume is accompanied by a change in temperature. A Gas When Compressed Becomes Heated, when it expands it absorbs heat and we notice a fall of its temperature. Con sequently, if we take, say 100 volumes of air at the temperature of this room and compress these 100 volumes into one volume the compressed air will be hot and will heat the vessel in which it is contained. But the heat, thus set free, can be carried off by placing the vessel in cold water, so that we may have 100 volumes of air compressed into one volume of normal temperature. Upon now permitting the compressed gas to expand it will absorb exactly as much heat as we took from it: in other words, the gas and its container will now show a temperature far below the normal. It is the ingenious application of this principle which has resulted in the liquefaction of all known gases, including hydrogen, argon, helium and atmospheric air. It is To-Day for the Second Time that liquid air is seen in Baltimore. As in the first case it again is New York air which we have as a fluid, not because Baltimore air is inferior to that of New York (in fact we Baltimoreans rather believe the reverse to be the case), but solely for the reason that the only apparatus for the liquefaction of air found in the Western Hemisphere has been built in the City of New York. We are indebted to the indefatigable efforts of Mr. Charles E. Tripler, extending over fully ten years, to his genius and skill in overcoming great difficulties of various kinds, that air can be and is now liquefied on a comparatively large scale and at a relatively low cost. While Mr. Tripler was not the first one to liquefy air, small quantities having been previously liquefied at an enormous cost by other investigators, he surely was the first one who rendered the process a practi let us take a glance at this drawing, representing the apparatus used for liquefying air. In order not to confuse your mind with a mass of details, all machinery, such as that furnishing steam and motive power, is omitted on this drawing, which simply gives an ideal representation of a cross-section of the apparatus. The three cylinders A represent compression pumps such as are used for pumping up a pneumatic bicycle tire, the only difference being that these here are worked by steam and are many hundred times more powerful than our hand pumps. Fresh air is taken through pipe I to the first pump Al and compressed to about one-tenth of its volume. This compressed, and consequently hot, air is passed through tubes surrounded by cold water circulating in tank B1 to absorb the heat set free by compression. The cooled compresed air passes to the next pump A2, where a higher pressure, about 1,000 pounds to the square inch, is applied. Again the air becomes hot, it again is cooled and this process is repeated a third time in pump A3 and cooler B3. The pressure applied in the third and last pump is between 2,000 and 2,400 pounds to the square inch; this is equal to about 144 tons to every square foot of surface with which the gas is in contact. While of course scientifically incorrect, figuratively we may say that by this enormous pressure the heat is pressed out of the gas, as we force water from a wet sponge. This immensely compressed gas next passes through the purifier C, where particles of dust are retained by filtration, and most of the moisture is removed by proper absorbents. Finally the purified, cooled, compressed gas passes through the inner bent tube (which is about thirty feet high) until it reaches the point D. Here the gas passes through a valve which permits its exit. The gas now suddenly expands, and in doing so reabsorbs exactly as much heat as we took from it by compression and cooling. The result is a very decided fall in temperature; but this cold gas is not permitted to escape into the room; it is made to pass backward on the outside of the tube containing the compressed gas, imparting to this a lower temperature. Cold compressed gas next issues from the valve and in expanding becomes colder than the first gas quantity. And as this process continues, i. e., as the pipe containing the compressed gas is continuously cooled to a lower and lower temperature, a point is finally reached at which all constituents of air cannot longer exist in the gaseous state. Cohesion of the gaseous molecules begins and liquefaction results. This change takes place at a temperature of nearly I B" reason is obvious. A constant evaporation takes place, and you naturally ask, why not store the liquid in an air-tight vessel? If we had done this the vessel and contents soon would have become warmer, and long before it had assumed the temperature of the surrounding air, a somewhat unpleasant occurrence would have happened, viz: our vessel, even if strongly built of steel, most likely would have been shattered into fragments in consequence of the increased, pressure exerted by the enclosed air. But even if our vessel had been strong enough to stand this enormous pressure, the liquid air thus shipped from New York never would have reached Baltimore. The constant absorption of heat by the liquid would have soon brought this to and above its critical temperature and on opening the stop-cock nothing but a stream of gaseous air would have issued from the opening. And yet we transported this liquid air in a practically open vessel. The reason that we can do so is that this air now is exactly as cold as when it left New York, i. e., it has a temperature of about 190° C. below freezing or 310 F. below zero. And that it retains this temperature is due to the same cause which prevents water boiling under normal pressure to rise above 100° C. All the Heat Absorbed by the Liquid on its Transport, and while standing here, has served to vaporize some of the liquid, and this evaporation will continue to take place until the last particle of liquid air has disappeared, but this last particle would be as cold as the whole mass is now. This principle of self-refrigeration has been used for thousands of years in the Orient, where porous vessels are employed for storing and keeping cool the drinking water. By the constant evaporation of water through the porous jar, the temperature of the liquid is kept far below that of the surrounding air. Let us Next Take a Look at the Liquid. Using an ordinary metallic dipper we can transfer the fluid to a beaker. For a while the liquid boils vigorously, absorbing heat from the vessel into which we poured it, as also from the air 200° C. below freezing. The liquefied air collects in the chamber, whence it is drawn off through the stop-cock E. The letters V indicate the positions of valves required to permit the air to enter and to prevent its exit. Let us Next Turn our Attention to Liquid Air Itself. Within this vessel, somewhat resembling an ice cream freezer, is a tin can, well covered with a lid of hair felt, and surrounded by the same material, which of course serves to some extent as a protection against the heat of the surrounding air. When this vessel left New York seven hours ago it contained about twelve liters (or three gallons) of liquid air. Though it was on the whole trip under the personal charge of the gentleman who brought it safely to this room, and though none of the valuable article has been spilled, there is a great deal (about 25 per cent) less of it now than when it left New York. The above it. It is this heat abstraction from the air which causes the appearance of clouds of mist, due to the condensation of atmospheric moisture, first into a liquid then also partly to a solid. Pouring the air on the floor we have the same appear: ance of a white cloud of fog. We also hear a peculiar crackling noise due to the same cause which produces similar sounds when water is dropped on red-hot iron. Looking at the liquid we find it to be of a turbid, or even a milky appearance. The reason is that at least two of the atmospheric constituents, viz: moisture and carbon dioxide, are present as solids, floating in the mixture of liquid nitrogen and oxygen. To obtain a clear liquid we have to filter the air, using ordinary filter paper for the purpose. In consequence of the great difference in the temperatures of our glass vessels and liquid air some care must be taken to prevent breakage. This you will realize if you consider that this difference here is between two and three times greater than between these glass vessels and boiling water. On filtering the air, as we do here, into ordinary beakers these become at once covered with moisture from the air, this moisture rapidly freezing into solid ice. To Prevent These Objectionable Phenomena these flasks (figure No. 8, page 333) or bulbs, known as Dewar's vacuum bulbs, may be used to advantage. These vessels are jacketed, i. e., there are two vessels, one within the other, having an annular space between the walls, and joined in a common neck Looking at our liquid air in the vacuum bulb we find it to be a perfectly transparent liquid showing a pale blue tinge. On standing the blue color becomes more intense, as the colorless but more volatile nitrogen escapes and the liquid becomes richer in blue oxygen. Next we Should Satisfy Ourselves that we have here a rather cold liquid by the sensation we experience when dipping our finger into the liquid. We may do this with proper care without suffering unpleasant consequences. The reason is exactly the same as that which prevents the burning of a moistened hand when dipped for a fraction of a second into molten iron. at the top. In the annular space, a very high vacuum is formed, which prevents the heat from being conducted from the outer to the inner wall, therefore we have no deposit of moisture, and moreover evaporation takes place very slowly, a teaspoonful requiring hours for evaporation. If a globule of mercury is placed in the annular space and the inner bulb is filled with liquid air, we soon see a beautiful mirror of frozen mercury forming on the bulb in consequence of the condensation of the mercury vapors diffused through the vacuum. This mirror acts as an additional safeguard against evaporation, as it reflects nearly all of the radiant heat which otherwise would enter the liquid. In both cases no direct contact between the hand and the liquid takes place. In one case the moisture of the hand forms vapor, preventing the molten iron from touching it, in our case here the liquid air forms a layer or cushion of gaseous air around our finger. Of course the exposure of our hand to the liquid should be scarcely more than instaneous, as otherwise this "scalding cold" liquid will damage the tissue seriously, causing frost-bites and injuries which heal very slowly. You will notice that the liquid does not wet your hand; it re mains perfectly dry on account of the air cushion which forms and prevents contact. Let us next examine into remarkable changes which take place in the molecular condition of different substances when cooled to nearly 200 C. below zero. For instance, iet us place pieces of paraffin and bands or balls of soft rubber into the liquid. On removing them they are found as brittle as badly cooled glass. The cooled paraffin crumbles down like starch, this solid rubber ball is broken into pieces by a stroke of the hammer. The Effect of Intense Cold on Different Metals (figures No. three and seven, page 333) differs widely. For instance, sheet iron and steel become so brittle that they readily break, while copper remains soft and malleable. As a general rule we may say that those metals which can be tempered, i. e., become nail into a hard board, or by casting a mercury bar on which we may suspend heavy weights, thus showing that it possesses considerable tensile strength. (Figure No. 10, page 334). Professor Tyndall by a series of highly ingenious experi ments demonstrated that ice is practically a plastic material. This is true of warm ice, i. e., ice at the freezing point. Let us make some cold ice and this surely no longer is plastic, but as you see crumbles into dust most readily. Pure Alcohol was formerly considered to be one of the few liquids which do not solidify on cooling. But then liquid air was unknown. If we pour alcohol into liquid air, the alcohol is converted into a snowy mass of crystals. By stirring this Experiments with Liquid Air. hard when heated to redness and cooled by dipping into water, are hardened directly by cooling to 190 C., while metals not acted on in this way by heating and sudden cooling i. e., metals which can be annealed, are also little affected by dipping into liquid air. It is of interest to note that while the pliability of iron and steel is greatly reduced at low temperatures, the tensile strength is nearly doubled. Mercury of course freezes rapidly, but while mercury when solidified by carbon dioxide is rather soft like lead, mercury when cooled to 190 is extremely hard, as we may show by casting a mercury hammer which we may use for driving a mass it is reduced to the condition of viscid sugar. In this condition it may be lifted out and frozen into a rigid mass by pouring more liquid air over it. It is needless to state that animal and vegetable matter, such as meat, eggs, beans, potatoes, etc., while yet containing moisture are converted into brittle masses which can be readily powdered. To the pharmaceutical profession it is of interest that the labor of disintegration is reduced to a minimum by cooling the materials before the operation is commenced. I took to the laboratory of Mr. Tripler a collection of about two dozen drugs selected as representatives of materials offering the greatest difficulties in powdering. These drugs included resins, gums, roots, barks, seeds and other materials, and every one of the specimens after proper cooling became brittle and convertible into powder without the least efforts. Let us quickly cool a few specimens, as for instance, aloes, nux vomica, sumbul and cotton bark. A few strokes with the pestle readily converts any of them into powder. And how many a weary hour have many of us spent in by-gone days in efforts to powder some of these obstinate drugs. All these experiments surely prove conclusively that in liquefied air we have an extremely cold material, and if we had time it might be of interest to briefly consider the methods by which these low temperatures are measured. But this I cannot do, as many other interesting phenomena claim our attention. The specific gravity of liquefied air is a trifle above that of water (viz: 0.94), consequently it floats on water, as we can demonstrate experimentally. What you will notice in a few minutes is that globules of gas sink below the surface of the water; the explanation is this: liquid nitrogen is specifically somewhat lighter than water (viz: 0.885), liquid oxygen slightly heavier (viz: 1.124); moreover nitrogen is more volatile than oxygen; consequently the liquid air floats on the water, but as the nitrogen escapes the remaining oxygen sinks below the surface, though it is generally carried upward again by the gaseous oxygen constantly forming. vessel, is comparable to the formation of steam in a steam- By quickly driving a cork into the open end of a strong Experiments With Liquid Air. some liquid air has been More Especially for the As the heat of the Bunsen flame had apparently very little effect on our liquid air, let us try the action of cold water. On pouring a 100 cc. of icecold water into our kettle the evolution of air-steam becomes most violent because the heat of the cold water is more rapidly communicated to the air, and if we next examine the contents of our kettle we find that our water has been converted into solid ice, notwithstanding that we had the kettle standing over the flame. The explanation is so obvious that I need not waste time in speaking further on the subject. 14. Burning Car That the Color of Many Substances is influenced by temperature is a wellknown fact. Heretofore we only had opportunities to experiment at ordinary and high temperatures. Liquid air now enables us to investigate colors at extremely low temperatures and 10. Frozen Bar of Mercury. 11. Liquid Oxygen in Water. as a general rule we may 12. Frozen Whiskey. 13. Carbonic Acid Snow. say that, if a color is bon in Liquid Air. -[Scientific American. affected at all, it passes on cooling to a lighter shade. For instance, this intensely red mercuric iodide turns to a pale yellow, when immersed in liquid air; a crystal of potassium dichromate changes from orange-red to yellowish-white. When experimenting in this direction I was surprised to find that the blue color of crystals of cupric sulphate is not affected at all. The anhydrous cupric sulphate being colorless I expected to see the blue crystals turn pale. As our theories regarding the exact molecular or atomic conditions of water of crystallization are far from satisfactory, an investigation of the subject by means of very low and high temperatures may lead to good results. The Constant Evaporation of Liquid Air, especially in a closed Some half hour ago I placed intentionally some liquid air in these vessels for partial and spontaneous evaporation. As stated before, the boiling point of liquid nitrogen is somewhat lower (194° C.) than that of liquid oxygen (181 C.); consequently, chiefly nitrogen escapes first from the mixture of the two elements. While in air we have about fourfifths nitrogen and one-fifth of oxygen; the liquid before us has now a very much larger proportion of oxygen; in fact it may have as much as 75 or 80 per cent of oxygen, only 20 to |