Vacuum Pumps
    The piston-type vacuum pump was invented by Otto von Guericke (1602-1686) in the course of a series of experiments on the production and effects of a vacuum. In his early experiments, ca. 1647, von Guericke produced a vacuum by using a suction pump to remove the water from a sealed wooden cask. Understandably, the cask leaked air in from the outside as the water was withdrawn, indicating the need to use glass or metal systems. The subsequent collapse of an imperfectly-formed vacuum vessel led him to conclude that the spherical shape was the most desirable one for withstanding a pressure difference. The drawing at the right shows the pumping of water from a spherical vessel to produce a vacuum. Eventually, he developed a pump which removed the air directly from the vessel, using air as the working fluid for the pump in place of the water formerly thought to be necessary.
   Otto Von Guericke was the Burgomeister, or Mayor, of Magdeburg, a town about 100 Km west and slightly south of Berlin during the years from 1646-1676. 

   In addition to his work with the production of a vacuum, von Guericke also produced an early electrostatic machine, although not with any intention of studying electrostatics.

   The diagram of the double-barrel air pump at the right dates from 1832, but was an old-fashioned design for the time. The valves V and V' allow a certain fraction of the air remaining in the receiver to enter the pump barrel as the piston is drawn up, and to be expelled as the piston goes down. The geared wheel W is rotated alternately left and right to actuate each cylinder in turn. The mercury barometer MH indicates the degree of exhaustion of the receiver. 
   If the effects of outgassing are ignored, the ultimate pressure that could be reached depends on the largest and smallest volumes of the pump barrel, the volume to be exhausted, and the number of pumping cycles used.  The very best pump in the 1887 Queen catalogue gave an ultimate pressure of about 0.002 atm. A modern mechanical pump should go to pressures 100 times lower than this.

   These modest pumps were designed for use in schools, and sold in the second-half of the nineteenth century for $15 to $20. The one on the left is in the apparatus collection of St. Patrick's College in Maynooth, County Kildare, Ireland, and the similar one on the right was in the store of James Kennedy Antiques in Durham, North Carolina when I visited in the spring of 2000. Both are unmarked.

   The small, unsigned vacuum pump at the left is in the collection of Denison University in Granville, Ohio. On the right is a small vacuum pump by William Harris of London, presently at the Smithsonian Institution. This may be the one described in the 1829 Harris catalogue as "A single-barrel Air Pump, with glass receiver", with prices running rom 2£ 15s. to 3£. 13s. 6d.
   The vacuum pump at the left is at Depauw University in Greencastle, Indiana. The notes from my visit in 1985 indicate that it was made by N. B. Chamberlain of Boston. If so, it dates from before ca. 1855 when Chamberlain joined forces with E. S. Ritchie for form Ritchie and Chamberlain. By 1860 the business was entirely in Ritchie's hands. 

   The 1860 Ritchie catalogue lists this pump in the $100 to $200 range, depending on the size of the cylinder (from 12x3.5 inches to 13x4.5 inches) and the diameter of the pump plate (from 12 inches to 15 inches in diameter) that is missing in this example. 

   Ritchie wrote that "The cylinder is highly polished, the piston packed in an improved manner, insuring a perfect contact with slight friction; the piston rod passes a stuffing box in the top of the cylinder, which is of cup form, to receive oil, which renders the packing air-tight, and lubricates sufficiently the piston and rod."

   The brass plate on the front of the pump at the left below at Hampden-Sydney College in Virginia, bears the maker's mark of Chamberlain and Ritchie and the date 1851. When I saw it it was in storage in a very hot attic. A similar pump (at the right, below), lacking the brass pump plate, is at the Wesleyan University in Middletown Connecticut. Wesleyan and founded in 1831, making this one of its earlier pieces of apparatus.

   The double-barrel pumps below are by Pixii of Paris. At the left is one on display at Transylvania University in Lexington Kentucky, while in the middle is one that was formerly in the collection of Kenyon College, and is now in storage at the Knox County, Ohio Historical Museum. With glass pump cylinders the cost was 370 francs ($75) in the 1849 Pixii catalogue, while the model with the metal cylinders was 360 francs. The rather dirty pump at the right is clearly the same as the first two, and I found it in storage at Dartmouth College.
   Union College, in Schenectady, New York, has a somewhat similar double-barreled vacuum pump with thick-walled glass cylinders. 

   The flat plate at the top of the pump bears the notation: "Joh. Mich. Eckling in Wien, Landstrasse No. 109."

   At one time the pump was encased in a wooden cabinet, and the pump plate was elevated to bring it above the top of the cabinet.

   As the nineteenth century began to wind down, table-top pumps like the one at the right began to be standard issue for college collections. This one, at Kenyon College in Gambier, Ohio, was made by James. W. Queen of Philadelphia; in the 1881 it cost $45, which included a syphon gauge to indicate the extent of the vacuum.

   The apparatus has a density of air sphere screwed into the pump plate. 

   A close examination of the pump shows that some of the brass fittings were made by the firm of Edward S. Ritchie of Boston. The 1860 Ritchie catalogue shows a series of connectors and stopcocks for use in repairing and modifying vacuum pumps.

   The hardware at the top of the pump at the left, below, resembles that of the Queen pump above. The pump barrel also looks quite a good deal like the Queen pump. This one was sold by Willyoung and Co. of Philadelphia, probably in the last years of the nineteenth century, and is in the collection of St. Mary's College in Notre Dame, Indiana. The pump at the left, below, from Denison University, is unmarked.
 The 1881 catalogue of E. S. Ritchie & Sons of Boston lists Ritchie's Patent Air Pump at the left at $250. This example at Dartmouth College is missing its 15 in. diameter pump plate. 

   The accompanying text notes that a vacuum of 1/50 inch of mercury could be obtained with the apparatus. 

   The neat double-barrel vacuum pump by Benjamin Pike, Jr. of New York is in the Collection of Richard Zitto of Columbiana, Ohio. It is listed in Vol. 1 of Pike's catalogue (1856) with prices of $22.50 and $25.00. A density of air sphere is shown attached to the pump plate. Double-barrel pumps are actuated by a rocking motion of the horizontal bar. Originally the pump had wooden handles projecting from the bar.
    This large, double-barrel vacuum pump is in the museum of St. Patrick's College in Maynooth, County Kildare, Ireland. It was made by the firm of John Frederick Newman, who worked in London from 1816 to 1860.

   In his 1837 catalogue, Newman lists this pump at £38 (about $190). 

  Ganot (in Elementary Treatise in Physics, 1885 edition) noted that "It is plain that when the rarefaction has proceeded to a considerable extent that the atmospheric pressure on top of [a single piston] will be very great, but it will be nearly balanced by the atmospheric pressure on the top of [a second] piston. Consequently the experimenter will have to overcome only the difference in the [pressures of the two cylinders]. This is the reason why two cylinders are employed." The two-cylinder pump is due to Francis Hauksbee, ca. 1700. 

   The apparatus catalogue of Max Kohl of Chemnitz, Germany, issued ca. 1900, lists this apparatus as a "Duplex pump, specially designed for the rapid production of very high vacua, suitable for exhausting incandescent lamps and Roentgen tubes." Its cost was 355 marks or about $90.

   The two-stage pump is on display at the Department of Physics at the University of Arkansas in Fayetteville.

  The small pump at the left is in the apparatus collection of Westminster College in western Pennyslvania. It has no maker's name.

   This pump plate (33 cm in diameter) and accompanying bell jar are in the Garland Collection of Classic Physics Apparatus at Vanderbilt University in Nashville, Tennessee.

   The two glass pumps below are diffusion pumps, used to evacuate systems lower than can be obtained with mechanical pumps. The earliest reference I have seen to diffusion pumps in the catalogues of standard laboratory suppliers is the 1929 Central Scientific Company catalogue.

   Early diffusion pumps used either mercury or oil as the working liquid. The right-hand pump below, from the Kenyon College chemistry department, shows the internal workings. The liquid is contained in the large reservoir at the bottom, and is boiled with an electric heater. The vapor rushes through the nozzles in the middle of the apparatus, and the curtain of vapor entrains residual air molecules in the vertical glass tube attached to the apparatus to be evacuated. The vapor molecules are condensed and draw back through the small glass tube across the bottom of the apparatus, and the remaining air molecules are pumped away by a mechanical pump attached to the right-hand arm. This form is sometimes called a Zabel pump, after its inventor.

   The glass pump at the left, below, is at the University of Arkansas at Fayetteville.

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