the present invention is a degassing tube which is characterized by the fact that ( a ) said tube has an inner tube and an outer tube which consist of porous resin tubes , and ( b ) a tube - form body which is formed from a porous polytetrafluoroethylene film with a mean pore size of 0 . 2 to 3 . 0 microns is interposed between said inner and outer tubes . the abovementioned inner and outer tubes which consist of porous synthetic resin tubes act to support and protect the abovementioned tube - form body which is formed from a porous polytetrafluoroethylene film . the aforementioned porous polytetrafluoroethylene film is the principal part which performs the degassing action of the present invention . specifically , as a result of the fine pores of the film and the water - repellent nature of the material itself , the film allows the permeation of gases but effectively prevents the permeation of water . by setting the pore size of the abovementioned porous film at 0 . 2 to 3 . 0 microns , it is possible to obtain a resistance to liquid pressure which is desirable for such a degassing operation , and at the same time to achieve an appropriate increase in the gas permeability of the film . a concrete practical working configuration of the present invention will be described below with reference to the attached figures : like conventional devices , the present invention also uses porous polytetrafluoroethylene tubes . in the present invention , however , as is shown in fig1 porous polytetrafluoroethylene tubes are used as an inner tube ( 1 ) and an outer tube ( 3 ), and a tube - form body ( 2 ) consisting of a porous polytetrafluoroethylene film ( 4 ) is interposed between the aforementioned inner and outer tubes ( 1 , 3 ). the aforementioned tube - form body ( 2 ) can easily be manufactured as follows : i . e ., both ends of a porous film ( 4 ) with a prescribed width are welded together ( 5 ) so that a tube - form body is formed as shown in fig2 . this tube - form body ( 2 ) is fit over the outside of the aforementioned tube ( 1 ), and the aforementioned tube ( 3 ) is fit over the outside of the tube - form body ( 2 ). the aforementioned porous film ( 4 ) is given a porous structure by flat rolling / drawing ; specifically , this film is obtained in a universally known manner as a spiderweb type structure with countless microfibers connecting numerous micronodes . this fine fiber structure acts in conjunction with the water - repellent characteristics of the resin itself so that the permeation of gases is allowed , while the passage of liquids ( especially water ) is prevented . accordingly , in the present invention , a tube - form body ( 2 ) formed from such a film ( 4 ) constitutes the main part which performs the degassing action of the invention . as a result , the pore size of the porous structure of the film is important . specifically , since a film is used , it is essential that the thickness of the film be only a fraction of the thickness used in the case of a tube , in order to increase the gas permeability . in concrete terms , the film thickness should be 30 to 100 microns . furthermore , the film can easily be formed with such a thickness by drawing , etc . under such conditions , the pore size of the pores formed between the aforementioned microfibers should be approximately 0 . 2 to 3 microns . specifically , in the case of a film in which this pore size exceeds 3 microns , a sufficient resistance to liquid pressure is not obtained . for example , in the case of a hydraulic pressure exceeding 0 . 8 kg / cm 2 , some water passes through so that an effective degassing action cannot be achieved . on the other hand , if this pore size is less than 0 . 2 microns , it becomes difficult to achieve an appropriate gas permeability . as an example , fig3 shows the relationship between hydraulic pressure resistance and gas permeability in the case of a polytetrafluoroethylene film with a mean pore size of 0 . 2 to 1 micron , a film thickness of 65 microns and a porosity of 85 percent . at a hydraulic pressure resistance of 1 . 0 kg / cm 2 , a gas permeability of 10 cc / cm 2 - sec is sufficiently guaranteed ; meanwhile , at a hydraulic pressure resistance of 0 . 5 kg / cm 2 , a gas permeability of 30 cc / cm 2 - sec can be sufficiently obtained . as was described above , the main part with a degassing function in the present invention is the aforementioned tube - form body ( 2 ) consisting of a porous polytetrafluoroethylene film ( 4 ). thus , in regard to the actions of the aformentioned inner tube ( 1 ) and outer tube ( 3 ), the technical nature of said tubes differs from that of conventional degassing tubes , even though said tubes may consist of the same porous polytetrafluoroethylene material as conventional degassing tubes . specifically , said tubes ( 1 , 3 ) act as supports and protectors of the aforementioned tube - form body ( 2 ). thus , the pore sizes and thicknesses , etc ., of these tubes are determined in this sense . furthermore , in regard to the material of said tubes , porous structures consisting of vinyl chloride or polypropylene resins , etc ., may be employed . the pore size of both of said tubes should be larger than the pore size of the aforementioned porous film ( 4 ). furthermore , a mesh - form porous material may be also be used for said tubes ; however , polytetrafluoroethylene tubes are desirable in order to present fouling or brusing of the tube - form body ( 2 ) consisting of the aforementioned film ( 4 ), and are desirable in cases where chemical resistance and heat resistance , etc ., are required . especially in the case of degassing tubes used in liquid chromatography , etc ., it is necessary to take elution into account ; in such cases , the use of such porous polytetrafluoroethylene tubes is desirable . a few examples of manufacture of the present invention will be described below : a tube - form body ( 2 ) consisting of a polytetrafluoroethylene film with a thickness of 50 microns , a porosity of 85 % and a pore size of 0 . 45 microns was fit over the outside of a polytetrafluoroethylene inner tube ( 1 ) with an external diameter of 7 . 2 mm , an internal diameter of 6 . 0 mm , a porosity of 50 % and a pore size of 3 . 5 microns . next , an outer tube ( 3 ) with an external diameter of 10 . 0 mm , an internal diameter of 8 . 0 mm and the same porosity and pore size as those of the aforementioned inner tube ( 1 ) was fit over the outside of the aforementioned tube - form body ( 2 ) to produce a product of the present invention . an aqueous solution at a temperature of 25 ° c . was fed into this tube of the present invention at a pressure of 1 . 5 kg / cm 2 , and a degassing treatment was performed with the area outside the tube in a vacuum state at 70 cmhg . as a result , the amount of air passing through the tube - form body ( 2 ) to the outside was 8 . 0 × 10 - 2 cc / cm 2 - sec . the water inside the tube passed through the inner tube ( 1 ) and reached the tube - form body ( 2 ), but did not leak from said tube - form body ( 2 ). thus , an effective degassing operation was successfully achieved . a tube - form body ( 2 ) consisting of a porous polytetrafluoroethylene film with a thickness of 50 microns , a porosity of 85 % and a pore size of 0 . 8 microns was fit over the outside of a polytetrafluoroethylene inner tube ( 1 ) with an external diameter of 7 . 2 mm , an internal diameter of 6 . 0 mm , a porosity of 70 % and a pore size of 1 . 0 microns . next , a polytetrafluoroethylene tube ( 3 ) with an external diameter of 10 . 0 mm , an internal diameter of 8 . 0 mm , a porosity of 70 % and a pore size of 1 . 0 microns was fit over the outside of the aforementioned tube - form body ( 2 ) to produce a product of the present invention . when a degassing treatment was performed using this product under the same conditions as in example of manufacture 1 , the degassing rate that was achieved was 5 . 0 × 10 - 2 cc / cm 2 - sec . furthermore , as in example of manufacture 1 , there was no leakage of water from the outside . as was described above , the present invention provides a high - performance degassing tube which is endowed with a high resistance to liquid pressure and a high gas permeability . accordingly , the present invention makes it possible to perform degassing treatments of liquids ( required for high precision in various industrial fields ) efficiently and inexpensively using a small apparatus . the present invention thus has great industrial merit . fig1 is a cross section of a tube of the present invention . fig2 is an oblique view of the tube - form body consisting of a porous polytetrafluoroethylene film used in the tube shown in fig1 . fig3 is a graph which illustrates the relationship between hydraulic pressure resistance and gas permeability for one example of the aforementioned porous polytetrafluoroethylene film . fig4 is a graph which illustrates the relationship between hydraulic pressure resistance and gas permeability for a conventional porous polytetrafluoroethylene tube . furthermore , in the aforementioned fig1 and 2 , ( 1 ) indicates an inner tube consisting of a porous tube , ( 2 ) indicates a tube - form body , ( 3 ) indicates an outer tube consisting of a porous tube , ( 4 ) indicates a porous polytetrafluoroethylene film which forms the aforementioned tube - form body , and ( 5 ) indicates a welded area . while the invention has been disclosed herein in connection with certain embodiments and detailed descriptions , it will be clear to one skilled in the art that modifications or variations of such details can be made without deviating from the gist of this invention , and such modifications or variations are considered to be within the scope of the claims hereinbelow .