a first embodiment of the present invention will be described with reference to fig1 . in fig1 gas feed pipe 8 is connected to rotating hollow shaft 3 with the interposition of sealing mechanism 8 &# 39 ;, and a plurality of stirring branch pipes 1 &# 39 ; are attached to the lower end of rotating hollow shaft 3 . each of the branch pipes 1 &# 39 ; is provided with a plurality of gas jet pipes 2 being opened at the lower ends thereof . while gas 11 fed through gas feed pipe 8 is jetted from the holes of gas jet pipe 2 through rotating hollow shaft 3 and branch pipes 1 &# 39 ;, rotating hollow shaft 3 is rotated by means of rotating mechanism 9 in order to bring solution or slurry solution 10 in storage tank 6 into contact with the jetted gas . as shown in fig1 the length of each gas jet pipes 2 is greater than the jump height of solution splashes , and therefore the problem of the splashes can be solved effectively . however , when the solution or the slurry solution which particularly contains solid constituents therein , streams into the horizontal stirring branch pipes 1 &# 39 ; at the termination of the operation , and when it is attempted to discharge the solution or the slurry solution from the pipes , such an attempt cannot be carried out successfully . accordingly , it is intended that each stirring branch pipe 1 &# 39 ; in fig1 is inclined by an angle of α to a horizontal plane as shown in fig2 . this constitution permits the solution or the slurry solution coming into the pipes to be discharged therefrom smoothly and perfectly at the resumption of the treating operation . fig3 ( a ) and 4 ( b ) show the circumstances that when gas jet pipe 2 is moved in the rotational direction indicated by the arrow , gaseous phase section 16 is formed , as in the case of a stirring rod in fig8 which will be described hereinafter . fig3 is concerned with an embodiment using gas jet pipe 2 which is circular in its sectional view , and fig4 ( a ) and 4 ( b ) are concerned with an embodiment using gas jet pipe 2 in which its front surface and back surface in the moving direction are convexly curved and flat , respectively , as most easily understood from fig4 ( b ). when gas jet pipe 2 shown in fig4 ( b ) is used , gas 11 jetted from the opening of pipe 2 is sucked into gaseous phase section 16 which is formed behind flat surface 2 &# 39 ; of the pipe , and gaseous phase section 16 is finely severed along its edge portion 17 by an eddy force generated with the aid of the rotary motion of the pipe in order to form substantially uniform fine bubbles 18 . this embodiment in fig4 ( a ) and 4 ( b ) can further improve a gas contact efficiency than the gas jet pipe in fig3 which is circular in the sectional view . such a sectional shape as the gas jet pipe in fig4 ( b ) can be applied to a stirring rod in fig6 and 7 which will be described hereinafter . a second embodiment of the present invention will be described in detail in reference to fig5 . in an apparatus shown in fig5 gas feed pipe 8 is connected to rotating hollow shaft 3 with the interposition of sealing mechanism 8 &# 39 ;, and a plurality of stirring blades 15 for stirring a solution or slurry solution 10 in storage tank 6 are attached to the lower end of rotating hollow shaft 3 . a plurality of stirring branch pipes 1 &# 39 ; are attached to rotating hollow shaft 3 above the stirring blades 15 , and each branch pipes 1 &# 39 ; is provided with a plurality of gas jet pipes 2 which are opened at their lower ends . according to this apparatus , rotating hollow shaft 3 is rotated by rotating mechanism 9 , while the gas 11 delivered through gas feed pipe 8 is jetted from the gas jet pipes 2 via rotating hollow shaft 3 and the branch pipes 1 &# 39 ;, in order to stir solution 10 in storage tank 6 and to thereby carry out a gas / solution contact treatment . the apparatus in fig5 is a variation of the embodiment in fig1 and in fig5 in which hollow rotating shaft 3 is downward prolonged and the stirring blades 15 are attached to the prolonged portion thereof . in consequence , solids are inhibited from precipitating on the bottom of storage tank 6 , and the solid concentration in solution 10 in the vicinity of the gas jet pipes 2 is lowered in order to decrease the trouble due to splashes in the gas jet pipes 2 . the variations shown in fig2 and fig4 ( a ) and 4 ( b ) can be applied also to the stirring branch pipes 1 &# 39 ; and the gas jet pipes 2 of this embodiment . fig6 shows a schematic view of a third embodiment for treating a solution or a slurry solution in accordance with the present invention . solution or slurry solution 10 is guided to storage tank 6 through feed orifice 7 . horizontal stirring rod 1 is attached to the lower end of hollow rotating shaft 3 downward extending in solution 10 , and a plurality of gas jet pipes 2 , which extend vertically downward , are fixedly attached to stirring rod 1 in the middle portions thereof . these gas jet pipes 2 are connected to hollow rotating shaft 3 with the interposition of branch pipes 4 . gas 11 is jetted into solution or slurry solution 10 through gas feed pipe 8 disposed above hollow rotating shaft 3 , the latter member 3 , the branch pipes 4 and the gas jet pipes 2 . on the other hand , stirring rod 1 rotated by rotating mechanism 9 forms a gaseous phase section behind rod 1 itself , and gas 11 is fed to this gaseous phase section through the gas jet pipes 2 . fig8 shows generation circumstances of gas bubbles in the apparatus shown in fig6 . when stirring rod 1 is rotated in the direction of arrow a at a rotational speed of 50 to 150 rpm , with gas 11 jetted through the gas jet pipes 2 , gaseous phase section 16 is formed all over the back surface of stirring rod 1 . gaseous phase section 16 is finely severed along its edge portion 17 , so that most of the gas in section 16 is changed into fine gas bubbles 18 . in this case , gaseous phase section 16 in the vicinity of rotating shaft 3 is narrow , and therefore at times the large gas bubbles are locally produced therein . the gas jet pipes 2 may be disposed at arbitrary positions on stirring rod 1 , to the extent that these positions are not close to rotating shaft 3 where the gaseous phase section is narrow . further , openings of the gas jet pipes 2 are provided so as to be located under the lower surface of stirring rod 1 , and the gas jet pipes 2 can be extended downward within the range in which gas 11 can be fed stably to the gaseous phase section . the gaseous phase section is also formed behind each gas jet pipe 2 , wherein such would contribute to the formation of the fine gas bubbles . during the treating operation , gas 11 is jetted as shown in fig8 and so the solution or the slurry solution does not flow backward into the gas jet pipes 2 . however , it is inevitable that on occasions splashes generated at the openings of the pipes 2 would gain entry into the pipes against the flow of the gas . unless the splashes are discharged from the pipes at an early stage , scales will develop therein . for this reason , the present invention contemplates that the gas jet pipes 2 are extended downward so as to dischage the splashes early from the pipes . therefore , a length of each gas jet pipe 2 should be determined , taking the height of the splash jump into consideration . in addition , the gas jet pipes 2 should be inclined within the range which does not prevent a downward natural stream of the splashes , which results from the weight thereof . further , when the inside walls of the gas jet pipes 2 are wetted , the splashes which have gained entry into the pipes 2 are prevented from obstinately adhering to the walls and the splashes can be discharged early therefrom . in the apparatus in fig6 a conduit for wash water 12 is connected to a conduit for feeding gas 11 to hollow rotating shaft 3 , so as to feed wash water 12 to the gas jet pipes 2 intermittently or continuously , with the result that the inside walls of the gas jet pipes 2 can be wetted . when the treating operation is stopped , solution or the slurry solution 10 flows into the gas jet pipes 2 , the branch pipes 4 and hollow rotating shaft 3 , but the development of the scales can be avoided by washing them with wash water 12 . usually , when the slurry solution flows thereinto , most of the solids having large specific gravities precipitate on the bottom of storage tank 6 and therefore these solids scarcely come into the pipes . however , for the purposes of avoiding the precipitation of the solids on the pipes and facilitating the washing operation of the pipes at the resumption of the treating operation , it is preferred that the pipes into which the slurry solution will flow , are constituted vertically or inclinatorily . in this connection , the variations shown in fig2 and fig4 ( a ) and 4 ( b ) can be applied to the branch pipes and the gas jet pipes in this embodiment . fig7 shows a fourth embodiment for treating a solution or a slurry solution in accordance with the present invention . different points than in fig6 are that two gas jet pipes 2 are mounted on one stirring rod 1 and that wash water feed pipe 14 is placed in hollow rotating shaft 3 and wash water nozzles 19 of feed pipe 14 are opened in the vicinity of the inlets of branch pipes 4 . fig9 is an enlarged view illustrating the wash water nozzles 19 . the employment of such a constitution permits ensuring the feed of gas 11 and uniformly jetting wash water 12 into the branch pipes 4 and the gas jet pipes 2 , so that a wet state can always be maintained all over the inside walls of the pipes 2 and 4 . by the use of the apparatus in fig6 air is jetted into an absorbing solution containing calcium sulfite which had been prepared in a wet exhaust gas desulfurizing installation , in order to carry out an oxidation treatment of calcium sulfite . the treating construction is as follows : the absorbing solution is first poured into a 6 - m - wide and 4 - m - long storage tank , until the depth of the absorbing solution has reached a level of 4 m . four stirring rods are horizontally attached to the lower end of a hollow rotating shaft having a diameter of 114 . 3 mm , the size of each stirring rod being 60 . 5 mm in diameter and 1 , 150 mm in length ( from the center of the rotating shaft ). each gas jet pipe has an inside diameter of 22 . 7 mm and an outside diameter of 27 . 2 mm , and the length of its vertical portion is 250 mm . further , each gas jet pipe is disposed at a position on the stirring rod , projecting 100 mm downward from the lower surface of the stirring rod , this position of the gas jet pipe thereon being a point which is 300 mm close to the center of the rod from its end portion . furthermore , a branch pipe for connecting the gas jet pipe to the rotating shaft is inclined at an angle of 15 ° to a horizontal plane . the attachment position of the stirring rod is 500 mm above the bottom of the storage tank . conditions for treatment are as follows : a concentration of the absorbing slurry solution is 17 wt % ( as gypsum ), a temperature of the slurry solution is within the range of 48 ° to 52 ° c ., throughout the solution is 3 . 7 kgmol / h in term of sulfites , a rotational speed of the stirring rod is 60 rpm , a feed rate of air is 400 m 3 n / h , a jet speed of air is 61 m / sec ( at 50 ° c . ), and the operation of the apparatus is carried out continuously for 700 hours ( about 1 month ). in the case of this operation , an oxidation ratio of the sulfites is 100 %. for the purpose of inspecting the inside walls of the gas jet pipes , the slurry solution is drawn out from the storage tank , while the aeration is kept up . the inside walls of the four gas jet pipes all has a similar thin gypsum scale over a length of about 40 mm from ends of the openings . in another case , the operation is continued under similar conditions for 1 , 500 hours ( about 2 months ), but the developing state of the scale is similar to that of the above case , and any particular development of the scale is not observed . an oxidation treatment of sulfites is carried out by the use of the same apparatus and under the same conditions as in application embodiment 1 except that wash water is fed thereto at a flow rate of 30 l / h for 10 seconds every minute . in the case of the operation for 700 hours ( about 1 month ), an oxidation ratio of the sulfites is 100 %. further , for the inspection of the inside walls of gas jet pipes , a slurry solution is drawn out from a storage tank , while aeration and the feed of wash water are retained . on the inside walls of the gas jet pipes , the generation of a scale is not found anywhere . a treatment is carried out by the use of the same apparatus as in fig1 and under the same conditions as in application embodiment 1 . the apparatus used in this comparative embodiment is different from the one shown in fig6 in that the stirring rods ( corresponding to stirring branch pipes ) are hollow and that 8 gas jet holes each having a diameter of 8 mm are provided under each stirring rod . conditions for operation are the same as in application embodiment 1 except that a jet rate of air through the gas jet holes is 60 m / sec . after 50 hours has elapsed , the operation is stopped owing to the vibration of the appratus itself . at this time , an oxidation ratio of sulfites is 100 %. the inside walls of the hollow stirring rods ( the stirring branch pipes ) are inspected , and it is found that a hard scale adhered to portions of the upper wall in each rod corresponding to the gas jet holes and that 2 to 4 of the jet holes in each stirring rod were clogged with the hard scale . in addition , a mixture of the hard scale and a soft scale adhered to other portions in each rod , as shown in fig1 . the occurrence of the hard scale on the upper walls of the rods indicates that splashes of the solution have clung to the walls . with regard to a jump height of the splashes , there is a difference between the gas jet pipes of application embodiment 1 and the gas jet holes of the above stirring rods , and this difference is considered to be attributable to a structural distinction between these pipes and holes . an oxidation treatment of sulfites is carried out by the use of the same apparatus and under the same operating conditions as in comparative embodiment 1 , and under the same washing conditions as in application embodiment 2 . for comparison , after 50 hours has elapsed , the operation is stopped as in comparative embodiment 1 , though such a vibration as in comparative embodiment 1 did not take place . at this time , an oxidation ratio of the sulfites is 100 %. the inside walls of hollow stirring rods ( stirring branch rods ) are inspected , and it is found that two gas jet holes in the vicinity of a rorating shaft and inside wall portions around these holes has no scale and thus they remained clear , but the two jet holes of each stirring rod which are further away from the rotating shaft are clogged with the scale , and the other adhering state of the scale is substantially similar to that of comparative embodiment 1 . therefore , it can be presumed that the apparatus will soon begin to vibrate .