1365April,1931THE CONSTRUCTION OFDEWAR FLASES[CONTRIBUTION VROMTHEDEPARTMENTOF CHEMISTRY OPTHE UNIVERSITY OPILLINOIS]THECONSTRUCTIONOFDEWARFLASKSBYT.E.PHIPPS,M.J.COPLEYANDE.J.SHAWRECEIYEDFaRRUARY10,1931POBLISED APRIL 6, 1931Amethod of making PyrexDewarflasks of considerablecapacityhasbeen developed which may be of interest to somewho have a limited orintermittentsupply of liquid air.Themost convenient size,in view of thelimited sizes of Pyrex flasks, is probablythree liters.The outerwall ismadeofa 5-liter fask.If 7-or S-liter flasks wereavailable,5-literDewarscould be constructed.However, with a 12-liter outer flask, silvering be-comes rather dificult, and the resulting flask is too bulky to bepractical.A heavy-walled 16-mm. tube, E in the figure, is sealed to the base of theneck of a 5-liter round-bottomed fiask.The heavy ring at the top of theneck is then cut off as closely as possible and the flask cut in two partsaround a great circle perpendicular totheaxis of theneck.The crack is shownatB.It ismadeby scratching a fileFEmark about an inch long on the flask,wrapping one turn of No.22 chromelAwire about the flask, and heating with acurrent of 10-12 amp.until the glass isfelt tobe warm 6-8mm.from thewire.Afewcc.of water is poured on the fileBmark.The crack obtained is often so-CCsmooth that there is dificulty in deter.mining therelativepositions previous tocracking.The inner fiask is preparedby cutting off the neck of a 3-liter flaskas closely as possible to the base of theFig.1.neck,A,and sealing on a previouslyfiared 40-mm.heavy-walled tube.This is then cut off so that it extendsthrough the neck of the outer fiask a distance about equal to that betweenthe walls of the neck.Thebottom half of the outer flask is placed in an asbestos-covered ironring.Aring ofbrass,D,such as a 20-mm.length of a 70-mm.brass tube isthen placed in the glass hemisphere, and the inner flask is set on it.Theupper half of the outer flask is put in place and clamped down with anotherasbestos-covered iron ring.The Dewar seal at thetop is then made usingtwo hand torches, one witha large air-gas fame,the other with a moderate6air-oxygen-gas flame,Obviouslythis must be done at a rather hightemperature, since the inner flask is essentially unstable.Blowing can bedone through the evacuating tube, but is usually unnecessary
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Phases or states of matterPhases or states of matter:The physical properties of solids, liquids, and gasesCHANGINGSTATEgascooing:particleslosingkineticenerayandsiowingdowngas condensing:particleslosingpotentialenergyandgettingcloserliquldcoong:particies losingTCK.E.andslowingdownliguid freezing:particles losingb.p.PE.andgettingclosersolidcooling1.p/m.p.freezingcompletefreezingbeginscondensingbeginscondensingcompleteTime7
7 Phases or states of matter The physical properties of solids, liquids, and gases Phases or states of matter:
Phases or states of matterLIOUIDSThe particles in a liquid are fairly well ordered over a shortdistance, but there is no long range order.The particles have more kinetic energy than in the solid state andit is this movement of the particles that disrupts the arrangementof the lattice.The potential energy of the particles is also greater than in solidsbecause they have moved apart slightly.At room temperature most substances which are liquid are:. covalently bonded molecular substances with quite strong vander Waals forces (large molecules with lots of electrons) orhydrogen bonded liquids such as water and alcohols.In an ideal liquid the behavior of a particle depends only on thenumber of other particles around it and not on their identityLiquid mixtures which behave in this way are said to obey8Raoult'slaw
8 Phases or states of matter The particles in a liquid are fairly well ordered over a short distance, but there is no long range order. The particles have more kinetic energy than in the solid state and it is this movement of the particles that disrupts the arrangement of the lattice. The potential energy of the particles is also greater than in solids because they have moved apart slightly. At room temperature most substances which are liquid are: ● covalently bonded molecular substances with quite strong van der Waals forces (large molecules with lots of electrons) or ● hydrogen bonded liquids such as water and alcohols. In an ideal liquid the behavior of a particle depends only on the number of other particles around it and not on their identity. Liquid mixtures which behave in this way are said to obey Raoult’s law. LIQUIDS
Phases or states of matterSOLIDSThe particles in a solid are arranged in an ordered latticeThe kinetic energy of the particles is low and they vibrate abouttheirlattice position.As the solid is heated the particles move moreand the lattice expands becoming more disordered.The potential energy of the particles is also low because they areclose together.9
9 Phases or states of matter The particles in a solid are arranged in an ordered lattice. The kinetic energy of the particles is low and they vibrate about their lattice position. As the solid is heated the particles move more and the lattice expands becoming more disordered. The potential energy of the particles is also low because they are close together. SOLIDS
Phases or states of matterSolids may be bonded in different ways.In metalsThe lattice energy depends on the charge on the metallic ions, thesize of theions, and the type of lattice.In ionic solidsThe lattice energy depends on the charge on the ions, the size of theions, and the type of lattice.In covalently bonded macromolecular solidsThe bond energy depends on the size of the atoms and thearrangement of the lattice.In covalentlybonded molecular solidsThe lattice energy depends on the forces between the molecules.These can be hydrogen bonds in compounds where hydrogen isbonded to nitrogen, oxygen, or fluorine (e.g. H,O); dipole forceswhere there is charge separation (e.g. CO2); van der Waals forceswhich depend on the number of electrons (e.g. noble gases)..10
10 Phases or states of matter Solids may be bonded in different ways: In metals The lattice energy depends on the charge on the metallic ions, the size of the ions, and the type of lattice. In ionic solids The lattice energy depends on the charge on the ions, the size of the ions, and the type of lattice. In covalently bonded macromolecular solids The bond energy depends on the size of the atoms and the arrangement of the lattice. In covalently bonded molecular solids The lattice energy depends on the forces between the molecules. These can be hydrogen bonds in compounds where hydrogen is bonded to nitrogen, oxygen, or fluorine (e.g. H2O); dipole forces where there is charge separation (e.g. CO2 ); van der Waals forces which depend on the number of electrons (e.g. noble gases)