in hemodialysis , the blood of a patient suffering from impaired kidney function is conducted from a patient blood - vessel ( of for example the patient forearm ) to a dialysis machine and is returned to the patient after the treatment . the blood is conducted along one side of a permeable membrane in a dialyser or filter working with and / or as a part of the dialysis machine . at the same time , a dialysis fluid may be conducted along the opposite side of the same membrane . a transfer of waste substances or poisons and excess water that are to be removed from the blood may take place by the help of diffusion through the membrane from the blood to the dialysis fluid . one dialysis treatment may typically last from about 3 to 8 about hours . in fig1 , a prior - art cartridge 1 for on - line preparation of a saturated bicarbonate solution from powdered sodium bicarbonate is shown . for the preparation of a dialysis fluid , the saturated sodium bicarbonate solution may be mixed with a solution comprising appropriate electrolytes , such as k + , ca 2 + and mg 2 + . the cartridge 1 may include a closed vessel or container 2 with an upper inlet end 3 and a lower outlet end 4 . within the vessel 2 , there is provided a supply of powder concentrate 5 of sufficient quantity so as to be suitable for one or more treatments . the quantity of the powder contained in the cartridge would be on the order of magnitude of 400 - 1500 grams . sodium chloride is another typical example in dialysis procedures . hereinafter a preferred embodiment of the inventive device for use in a powder or granulate cartridge will be described . a device 6 according to the invention is shown in fig2 . the device comprises an elongated , and in some embodiments substantially conical tube 6 made typically of a plastic such as polypropylene . the tube 6 isclosed at its lower end 7 and open at its upper end 8 . in the wall 9 of the tube 6 through holes 10 are provided . this particular embodiment has eight holes 10 arranged in pairs on opposite sides of the tube 6 . furthermore , the device 6 is provided with a neck portion 11 , which may be provided with engagement means , such as flanges or threads 11 ′. in fig3 , a device 6 attached to a lid 12 of a cartridge is shown . preferably , the neck portion 11 and the lid 12 are constructed so that the device 6 can be snapped onto the lid 12 . alternatively , the device 6 and the lid 12 can be made as an integral unit . it is appreciated that the inventive device 6 as well as the cartridge 13 ( vessel 14 and lid 12 ) ( see e . g . fig4 ) can be made of other materials than polypropylene . in fig4 , an embodiment of the inventive cartridge is shown . the cartridge 13 may be made of a polypropylene ( or other material ) vessel or container 14 and a polypropylene ( or other material ) lid 12 . the lid 12 has a liquid permeable inlet 16 . a solvent , which is to be introduced into the cartridge 13 , may be supplied via a tube 17 . in the bottom end of the vessel 14 a liquid permeable outlet 18 is provided . a tube 19 for discharge of a solution may be connected to the outlet 18 . the tubes 17 and 19 may not necessarily form part of the inventive cartridge . furthermore , the cartridge 13 has a conical tube 6 as disclosed above ( cf . fig2 ) connected at its neck portion 11 to the lid 12 . the embodiment of the device 6 shown in fig4 comprises two elongated flanges or ridges 15 a , 15 b . the ridges 15 a , 15 b are arranged longitudinally along and on the inside of the device 6 . these ridges 15 a , 15 b may act as “ fluid guides ”. the incoming fluid may then follow the inside wall of the tube 6 or flow along the ridges 15 a , 15 b . the “ fluid guides ” may alternatively consist of plastic pellets . an inventive cartridge may be manufactured according to the following . reference is made to fig4 and 5 . a vessel 14 is provided and a batch of powder or granulate 20 is poured into the vessel 14 . a tightly fitting lid 12 is attached to the vessel 14 so that the tube 6 is stuck into the powder bed 20 . the lid 12 may be threaded or may be welded to the vessel 14 . alternatively , using a self - containing cartridge , the powder may be sucked into the vessel 14 through some kind of membrane . in use ( see fig5 and 6 ), first air is sucked from the cartridge 13 for the purpose of creating a vacuum in the cartridge . then the cartridge is primed with a solvent , such as water , by letting solvent flow into the cartridge at a relatively high flow rate of about 1000 ml / min . it should be noted that the air removal and water priming may occur substantially simultaneously . in fig5 a primed cartridge is shown . the solvent may be introduced either through the upper inlet 16 or the lower outlet 18 , then having dual purpose , i . e . inlet at priming and outlet of saturated solution . in this example , the powder 20 may be sodium bicarbonate , and then the solvent 21 should be present in a sufficient amount so that the liquid level 22 is above the surface 23 of the powder bed 20 . the powder 20 is dissolved in the solvent 21 and a saturated sodium bicarbonate solution may leave the cartridge 13 through the outlet 18 . new solvent 21 is gradually entering the cartridge 13 , at a relatively low flow rate which is less than or about the same as the rate of solution leaving the cartridge and may be of about 15 ml / min . the sodium bicarbonate solution may then be mixed outside the cartridge with a fluid containing electrolytes for yielding a dialysis fluid . at least the lower holes of the tube 6 should be situated below the fluid level 22 and the fluid outlets 10 should be “ directed ” substantially towards the vessel wall so that the outflow of solvent 21 from the tube 6 is directed substantially horizontally , i . e . in parallel with the fluid level 22 , as shown in fig6 . the incoming fluid may then be prevented from freely falling in drops down to the fluid surface . the pressure waves and the currents will then be directed towards the wall of the vessel and dampened out before they reach the powder bed 20 . the channeling effect is minimized . tests have shown that the functioning time before an alarm is triggered can be prolonged as much as two hours compared to when using a prior - art cartridge intended for example for 8 h of use . it should be noted that the cartridge 13 may also be formed without a lid , either as a closed vessel or an open vessel ( not shown ). it is easily appreciated that the inventive device can be applied together with other types of cartridges , and the inventive idea for cartridges containing other substances than sodium bicarbonate . it is further appreciated that the inventive idea can be applied for other medical purposes than hemodialysis , such as for replacements fluids for hemodiafiltration and hemofiltration .