or twice, and you will obtain a washing which contains no ammonia; it is only superficial." Liquid ammonia (liquor ammonia), or the aqueous solution of ammonia of commerce contains varying quantities of ammonia in water, according to temperature. A mean usually stated is that water dissolves 700 volumes of the gas. At 0° C., 0.875 gramme or 1,148 cubic centimeters of ammonia gas are absorbed by one gramme of water under normal pressure. The avidity of the combination is attended with the evolution of heat, and this fact is demonstrated by passing a current of air through a cold concentrated solution of ammonia, displacing the gas, which carries off the heat of the intruded air, and the liquid falls below -40°, so that by this method mercury may be frozen. At ordinary temperatures, ammonia is a transparent gas, alkaline in reaction, colorless unless the air contains a little hydrochloric acid, when visible white fumes appear. Its tension at different temperatures varies greatly. The volumes of ammonia gas at different temperatures are, according to Andréeff, as follows: Temperature. Volume 10° C. 0° C. +10° C. + 20° C. 1.000 1.0215 1.0450 The coefficient of expansion between -11° and 0° C. is, according to the mean of three observations by Jolly, 0.00155; so that at temperatures sufficiently removed from its boiling-point ammonia expands more than a gas. At -38.5, according to Regnault, or at-350.7, according to Loir and Drion, ammonia is liquid at atmospheric pressure. By a mixture of chloride of calcium and ice Guyton de Morveau condensed ammonia into a liquid at -52°C., and Bunsen at -40° C. Guyton de Morveau's original experiment, in which he liquefied ammonia at -21°C., shows the influence of an admixture of water in changing the properties of ammonia, an influence which Ch. Tellier had discovered when he recommended and patented the liquefaction by pressure of anhydrous ammonia in icemachines. The specific gravity of the liquefied anhydrous ammonia is 0.76, and it is a colorless, very mobile liquid, refracting light more powerfully than water. Faraday solidified it at -103° Fahr., when its vapor tension was still 5 pounds to the square inch. The pressures and temperatures at which ammonia gas, dried by chlo ride of calcium or fused caustic potash, could alone be liquefied, led to the idea, until Tellier dispelled it, that for the purposes of artificial refrigeration it could only be used with water. Prof. F. A. P. Barnard, of New York, one of the commissioners at the Paris Universal Exposition of 1867, wrote in the report I have elsewhere quoted a very clear and definite statement of the views then entertained. M. Tellier's patent was in the secret archives of the French patent-office, and indeed the diffi culties in the way of pumping ammonia gas had led him to resort by preference to another agent, patented simultaneously, viz, methylic ether. Professor Barnard says: "Gaseous ammonia is reduced to the liquid form by pressure; but at 20° C. (68° Fahr.) it requires a pressure of not less than eight and a half atmospheres to produce liquefaction, and at 255 C. (77° Fahr.) not less than ten. Thus the pressure required rises very rapidly with the temperature. On the other hand, to liquefy ammonia by cold merely, under the ordinary atmospheric pressure, requires a reduction of temperature down to 38°.5 below zero of the Centigrade thermometer. Ammonia, therefore, evaporates very rapidly even at temperatures extremely low; and as the latent heat of its vapor is great, being estimated at 514° C., it may be used as a powerful means of producing cold, provided any practicable method can be devised for removing the vapor as it is formed. To do this mechanically would require a pump of large dimensions; and inasmuch as considerations of economy as well as of health and the comfort of the operators would require that the vapor should be reduced by compression to the liquid state, the pump should be capable of exerting a pressure of from seven to ten atmospheres. If, therefore, it were only by mechanical means that ammonia could be condensed, this substance could not be profitably used as a means of producing cold." To show what at that time was meant by liquid ammonia, and the views Professor Barnard entertained of the unequalled value of ammonia vapor for the abstraction of heat, I have another passage to quote. He says: "It may thus be stated that the latent heat of a kilogram of liquid ammonia is equal to ninety calories.* The latent heat of a kilogram of its vapor, that is to say, of ammoniacal gas, amounts to five hundred and fourteen calories. The latent heat of water, liberated in the act of congelation, is equal to seventy-nine calories per kilogram; so that one kilogram of ammonia would be capable by its evaporation of freezing six and one-half kilograms of water taken at the initial temperature of zero, or five kilograms taken at the temperature of 24° C. (750.2 Fahr.)." Alcohol absorbs ammonia readily. Messrs. Roscoe and Schorlemmer, in their admirable Treatise on Chemistry, furnish the following illustration and remarks: "The condensation of ammonia by pressure and the production of cold by its evaporation can easily be shown by the following experiment: The apparatus required for this purpose consists essentially of two strong glass tubes (a and b), which are closed below and are connected together by the tubes (e c) and (d d). The tube (d d) ends at (1) in a narrower tube (mm), which is at this point melted into a tube (a). The tube (a) is three-fourths filled with an alcoholic solution of ammonia saturated at 8°, and then placed in the cylinder (A). The syphon-tube (g) and the tube (ƒƒ), which reach to the bottom of the *A French calorie signifies the amount of heat required to raise the temperature of a kilogram of water, taken at 0° C. of temperature, 1° C., and this is adopted as a unit. +I am indebted to Messrs. D. Appleton & Co. for the use of this cut. cylinder, are fixed in position through the cork. In order now to perform the experiment, the cylinder (A) is nearly filled with warm water; the glass stop-cock (h) is opened, and the tube (b) placed in ice-cold water. The water contained in the flask is now quickly boiled, and thus the water in (A) is rapidly heated to 1000, and the ammonia gas driven out of solution until by its own pressure it liquefies in (b). As soon as the condensation of liquid ammonia ceases, the ebullition is stopped, and a portion of the hot water is withdrawn from the cylinder by means of the syphon (g); cold water is allowed to enter the cylinder, and after awhile this is replaced by ice-cold water. The cylinder (B) is now removed, when the liquefied ammonia begins to evaporate, and is again absorbed by the alcohol, though only slowly. But on closing the stop-cock (h) the gas above the alcohol is quickly absorbed, and thus the equilibrium is disturbed. The ammonia now passes rapidly through the tube (mm), and is absorbed so quickly that the liquid ammonia in (h) begins to boil, by which the temperature is so much lowered that if a test-tube containing water is placed outside (h) it is soon filled with ice." 0.-THE PROGRESSIVE STAGES IN ICE-MAKING INVENTIONS. After Cullen's efforts to freeze water in the receiver of a vacuum-pump, by the rapid vaporization of ether, we have to skip to the second quar ter of the current century for a practical step in the direction of artificialice-machines. JacobPerkins, whilst a resident in London, devoted himself to the determination of the compressibility of gases and fluids, and as I have stated elsewhere, he undoubtedly recognized that gases and vapors might be condensed into liquids. This property he took advantage of in 1834, in his "Apparatus for Producing Ice and Cooling Fluids." "The object of my invention," said Perkins in his English patent, "is so to use a volatile fluid that the same (having been evaporated by the heat or caloric contained in the fluid about to be reduced in temperature) shall be condensed and come again into the vessel to be again evaporated and carry off further quantities of caloric." "Description of the drawing.-a is a cistern for containing the water or other fluid from which it is desired to remove the caloric, and thus reduce its temperature, and even produce ice. This vessel should be well covered in and surrounded by a non-conducting material, in order to prevent the atmosphere or surrounding bodies giving off heat to the water or other fluid contained in such cistern; b is a vessel which is to contain the volatile fluid to be evaporated, and I chiefly recommend ether as the material to be evaporated, owing to the low degree of temperature at which, under ordinary circumstances, it becomes aeriform, but under the circumstances hereafter explained it will evaporate at still lower degrees of temperature; e is an ordinary pump, which I term the vapour-pump, it being intended to withdraw the vapour as it is generated in the vessel b, and to force it through the refrigerating-pipes d, contained in the cooling-tank e. There is to be a constant supply of cold water to the refrigerating-tank or vessel e, in order to cool down and condense the vapour in the pipes d. f is a pipe leading from the vessel b to the pump, having a valve to close the entrance into the pump, in order to prevent the vapour being forced back into the vessel b on the return stroke of the piston; g is a pipe having a valve opening outwards from the pump. This pipe g connects the pump with the refrigerator-pipes d; consequently the vapour, on coming into the pump, will be forced into the pipes d, and be there condensed, and thence return again into the vessel b to be again evaporated. But in order to secure a perfect condensation, I employ a valve, h, moderately weighted, say about atmospheric pressure, which prevents the return of the condensed ether till the same has become compressed and forced to give off its caloric to the condensing water on the outside of the condensing-tube d. The valve h is placed between the condenser and the vessel b, as shown in the drawing. It will be seen that most of the parts are shown in sections, in order that their construction may be evident. "The apparatus being arranged as above described, and as shown in the drawing, I now prepare it for commencing work by filling every part of the apparatus with the volatile liquid to the utter exclusion of the atmospheric air, after which a sufficient quantity of the liquid is drawn off by the small pump attached to the valve h, to make sufficient space |