100g of an aqueous solution of &# 34 ; class 3 water glass &# 34 ;, of which the sio 2 concentration was adjusted to 8 . 6 % by weight , was mixed with 100g of an &# 34 ; h type &# 34 ; cation exchange resin and stirred for 5 minutes . after stirring and removing the cation exchange resin by filtration , 60g of a silicic acid solution having an na concentration of 0 . 02 % by weight was obtained . the ph of the solution was adjusted to 8 . 8 by adding 2ml of in - naoh thereto and stirring . the viscosity of the solution rapidly increased and the solution set to a gel at about 30 seconds after adding the naoh . the gel was again converted to a liquid by allowing it to stand for 24 hours in a vessel the inside temperature of which was maintained at 60 ° c . by the liquefication , a solution of highly polymerized silicic acid having a 7 . 9 % sio 2 concentration and 0 . 10 % na concentration was obtained . the limiting viscosity and mean molecular weight of the solution were determined by using a ubbelohde viscosity meter and a molecular - weight fractionation method with ultrafilters , respectively . the limiting viscosity was 0 . 29 ( 100ml / g ) and the mean molecular weight was about 280 , 000 ( g / mol ). 100g of an aqueous solution of &# 34 ; class 3 water glass &# 34 ;, of which the sio 2 concentration was adjusted to 9 . 0 %, was mixed with 200g of an &# 34 ; h type &# 34 ; cation exchange resin and stirred for 5 minutes . after stirring and removing the cation exchange resin by filtration , 90g of a silicic acid solution having a 9 . 0 % sio 2 concentration and 0 . 01 % na concentration by weight was obtained . the ph of the solution was adjusted to 8 . 8 by adding 3 . 0 ml of in - naoh thereto and stirring . the solution set to a gel at 30 sec . after adding the naoh . the gel was liquefied by allowing it to stand for 24 hr . in a vessel the inside temperature of which was maintained at 60 ° c . the solution obtained by the above liquefication of gel was further stored in a vessel the inside temperature of which was kept at 20 ° c . for 18 months . it was determined by the same methods as in example 1 that the sio 2 concentration , na concentration , limiting viscosity and mean molecular weight of the solution stored for 18 months were respectively as follows : ______________________________________sio . sub . 2 8 . 7 % na concentration 0 . 084 % limiting viscosity 0 . 27 ( 100 ml / g ) mean molecular weight about 270 , 000 ( g / mol ) ______________________________________ 2 kg of an aqueous solution of &# 34 ; class 3 water glass &# 34 ;, of which the sio 2 concentration was adjusted to 8 . 6 %, was mixed with 2 kg of an &# 34 ; h type &# 34 ; cation exchange resin and stirred for 5 minutes . after stirring and removing the cation exchange resin by filtration , 1 . 8 kg of a silicic acid solution having a 0 . 02 % na concentration and 8 . 0 % sio 2 concentration was obtained . 60 ml of in - naoh was added to the solution for the purpose of ph adjustment . the solution set to a gel at 30 sec . after adding naoh . the gel was liquefied by allowing it to stand for 24 hours in a vessel the inside temperature of which was maintained at 60 ° c . the silicic acid solution thus obtained by the liquefication was further concentrated by using a rotary evaporator to increase the concentration 2 . 5 times . ( the rotary evaporator was operated at 75 ° c ., 40rpm and 20 - 150mmhg .) the sio 2 concentration , na concentration , limiting viscosity and mean molecular weight of the silicic acid solution after being concentrated were determined to be as follows : ______________________________________sio . sub . 2 concentration 18 . 8 % na concentration 0 . 26 % limiting viscosity 0 . 28 ( 100 ml / g ) mean molecular weight about 280 , 000 ( g / mol ) ______________________________________ 1 kg of an aqueous solution of &# 34 ; class 3 water glass &# 34 ;, of which the sio 2 concentration was adjusted to 4 . 3 %, was passed through a bed having a height of 32cm of an &# 34 ; h type &# 34 ; cation exchange resin which was disposed in a filter cylinder having an inside diameter of 5 cm . with a passing rate of 2 m / hr . 900 g of filtrate having an sio 2 concentration of 3 % and an na concentration of 0 . 004 % was obtained . to the filtrate was added 8 ml of in - naoh with stirring by using a magnetic stirrer so that the ph was adjusted to 8 . 8 %. the solution was allowed to stand at a temperature of 20 ° c . the viscosity of the solution gradually increased , and the solution set to a gel at 13 hours after the start of standing . the gel was liquefied by further allowing it to stand for 24 hours in a vessel the inside temperature of which was maintained at 60 ° c . the liquefied solution was concentrated by using a rotary evaporator to increase the concentration two times . ( the rotary evaporator was operated at 75 ° c ., 40 rpm and 20 - 150 mmhg .) the sio 2 concentration , na concentration , limiting viscosity and mean molecular weight of the concentrated solution were determined to be as follows : ______________________________________sio . sub . 2 concentration 8 . 6 % na concentration 0 . 048 % limiting viscosity 0 . 23 ( 100 ml / g ) mean molecular weight about 260 , 000 ( g / mol ) ______________________________________ 500g of an aqueous solution of potassium silicate , of which the sio 2 concentration was adjusted to 8 . 6 %, was mixed with 500 g of &# 34 ; h type &# 34 ; cation exchange resin and stirred for 5 minutes by using a magnetic stirrer . then , after removing the cation exchange resin by filtration , 14 ml of 1n - naoh was added to the solution . the viscosity of solution rapidly increased and the solution gelled at sec . after the addition of naoh . the gel was liquefied by allowing it to stand for 24 hours in a vessel the inside temperature of which was maintained at 60 ° c . the sio 2 concentration , potassium concentration , limiting viscosity and mean molecular weight of the liquefied solution were determined to be as follows : ______________________________________sio . sub . 2 concentration 8 . 4 % k concentration 0 . 076 % limiting viscosity 0 . 29 ( 100 ml / g ) mean molecular weight about 280 , 000 ( g / mol ) ______________________________________ by combining the polymerized silicic acid obtained in example 3 with three different metal salts ( ferric chloride , ferric nitrate and ferric sulphide ), twelve samples of flocculants having a total concentration of effective components ( sio 2 + fe 2 o 3 ) of 10 . 0 %, 12 . 5 %, 15 . 0 % or 17 . 5 % were prepared as follows : the solution of polymerized silicic acid prepared in example 3 was divided into twelve samples ( samples 1 through 12 ). to each sample distilled water and metal salt were added . that is , ferric chloride was added to four samples of a first group ( samples 1 to 4 ferric nitrate was added to four samples of a second group ( samples 5 to 8 ) and ferric sulphide was added to four samples of a third group ( samples 9 to 12 ), so that the mol ratio of si : fe in each sample was 3 : 1 . the solution of polymerized silicic acid obtained in example was divided into three samples ( samples 13 to 15 ). to each sample was added distilled water and a different metal salt , that is , sample 13 ( ferric chloride ), sample 14 ( ferric nitrate ) and sample 15 ( ferric sulphide ), so that the mol ratio of si : fe and the total concentration of effective components ( sio 2 + fe 2 o 3 ) in each sample was 3 : 1 and 10 %, respectively . three samples for comparison were prepared by using a highly polymerized silicic acid solution which was not subjected to a treatment to remove alkali metal and has a high total concentration of effective components , as follows : 640 g of an aqueous solution of &# 34 ; class 3 water glass &# 34 ;, of which the sio 2 concentration was adjusted to 11 . 0 %, was mixed with 160 ml of 5 . 4n - hcl with stirring . 800 g of a silicic acid solution having a ph of 2 . 0 and sio 2 concentration of 8 . 8 % was obtained . the solution was polymerized by slowly stirring for 30 minutes in a vessel the temperature of which was maintained at 60 ° c . a solution of polymerized silicic acid having a limiting viscosity of 0 . 30 ( 100 ml / g ) and a mean molecular weight of about 350 , 000 ( g / mol ) was obtained . the silicic acid solution thus obtained , of which the na concentration was not reduced , was divided into three samples ( samples 16 to 18 ). to each sample was added a different metal salt , that is , sample 16 ( ferric chloride ), sample 17 ( ferric nitrate ) and sample 18 ( ferric sulphide ), so that the mol ratio of si : fe in each sample was 3 : 1 and the total concentration of effective components ( sio 2 + fe 2 o 3 ) was 10 %. eighteen samples of flocculants ( samples through 18 ) prepared in example 6 , example 7 and example 8 were subjected to a test for their determining gel times by keeping them in two vessels the temperatures of which were maintained constant at 60 ° c . and 20 ° c ., respectively . table 1__________________________________________________________________________sample added mol . ratio con . (%) gel time ( hr .) no . salt ( si : fe ) ( sio . sub . 2 + fe . sub . 2 o . sub . 3 ) ph ( 60 ° c .) ( 20 ° c .) __________________________________________________________________________ 1 fecl . sub . 3 3 : 1 10 . 0 1 . 5 110 8800 2 &# 34 ; &# 34 ; 12 . 5 1 . 3 95 6000 3 &# 34 ; &# 34 ; 15 . 0 1 . 3 50 2650 4 &# 34 ; &# 34 ; 17 . 5 1 . 2 30 1100 5 fe ( no . sub . 3 ). sub . 3 &# 34 ; 10 . 0 1 . 1 360 & gt ; 12000 6 &# 34 ; &# 34 ; 12 . 5 0 . 9 190 8800 7 &# 34 ; &# 34 ; 15 . 0 0 . 8 90 3850 8 &# 34 ; &# 34 ; 17 . 5 0 . 6 48 2400 9 fe ( so . sub . 4 ). sub . 3 &# 34 ; 10 . 0 1 . 3 35 110010 &# 34 ; &# 34 ; 12 . 5 1 . 1 20 12011 &# 34 ; &# 34 ; 15 . 0 1 . 0 10 5012 &# 34 ; &# 34 ; 17 . 5 0 . 9 8 2513 fecl . sub . 3 &# 34 ; 10 . 0 1 . 4 95 & gt ; 430014 fe ( no . sub . 3 ). sub . 3 &# 34 ; &# 34 ; 1 . 1 240 & gt ; 430015 fe ( so . sub . 4 ). sub . 3 &# 34 ; &# 34 ; 1 . 3 35 110016 fecl . sub . 3 &# 34 ; 10 . 0 1 . 5 2 3017 fe ( no . sub . 3 ). sub . 3 &# 34 ; &# 34 ; 1 . 1 4 5018 fe ( so . sub . 4 ). sub . 3 &# 34 ; &# 34 ; 1 . 3 0 . 5 6__________________________________________________________________________ as can be seen from table 1 , the flocculants of the invention containing the silicic acid solution which was subjected to the treatment for removing alkali metral ( sampels 1 to 15 ) showed excellent stability where the total concentration of effective components was 10 % or more , while the flocculants containing the silicic acid solution which was not subjected to such an alkali metal removing treatment ( samples 16 to 17 ) had gel times of not more than several tens of hours at 20 ° c . when the concentration of effective components was 10 %. especially , the flocculants of the invention which contain fecl 3 or fe ( no 3 ) 3 as a metal salt remained stable without gelling for about 1000 to 4000 hours at 20 ° c . even when the total concentration of effective components was in a very high range such as 15 . 0 to 17 . 5 %. then , the flocculants of samples 1 to 15 were subjected to jar test , for the purpose of confirming the coagulating capability , as follows : each sample of flocculant was poured with stirring into test water having a turbidity of 100 degrees , alkalinity of 60 mg / 1 ( as caco 3 ) and a ph of 7 . 5 which was prepared by adding kaolin and nahco 3 to distilled water . the flocculant was used at a rate of 2 . 0 mg / 1 as fe and stirred for 7 minutes at a speed of 120 rpm ( at starting ) and 30 rpm ( at 3 minutes after starting ). the time when flocus appeared after the start of stirring , the average size of flocs and the turbidity of the treated water are shown in table 2 . table 2______________________________________sample floc appearance average water turbidityno . time ( sec .) floc size ( mm ) ( degree ) ______________________________________ 1 30 2 . 0 - 5 . 0 0 . 6 2 30 2 . 0 - 5 . 0 0 . 8 3 30 2 . 0 - 5 . 0 0 . 6 4 30 2 . 0 - 5 . 0 0 . 8 5 30 2 . 0 - 5 . 0 0 . 6 6 30 2 . 0 - 5 . 0 0 . 8 7 30 2 . 0 - 5 . 0 0 . 8 8 30 2 . 0 - 5 . 0 0 . 7 9 30 2 . 0 - 5 . 0 0 . 710 30 2 . 0 - 5 . 0 0 . 811 30 2 . 0 - 5 . 0 0 . 612 30 2 . 0 - 5 . 0 0 . 813 30 2 . 0 - 5 . 0 0 . 714 30 2 . 0 - 5 . 0 0 . 915 30 2 . 0 - 5 . 0 0 . 6______________________________________ as can be seen from table 2 , it was confirmed that the flocculants of the invention showed excellent results in each of floc appearance time , floc size and water turbidity after treatment . the flocculant obtained in example 2 which was stored for 18 months after preparation was subjected to a jar test for confirming its coagulating capability after long term storage , as follows : 100 g of a flocculant of which the mol ratio of si : fe was 3 : 1 and the total concentration of effective components ( sio 2 + fe 2 o 3 ) was 10 %, was prepared by adding 10 . 4 g of ferric chloride ( fecl 3 . 6h 2 o ) and water to the solution of polymerized silicic acid obtained in example 2 . the flocculant was poured into a test water having a turbidity of 100 degrees , an alkalinity of 60 mg / 1 ( as caco 3 ) and a ph of 7 . 5 , which was prepared by adding kaolin and nahco 3 to distilled water . the pouring rate of flocculant was 20 mg / 1 as fe and stirring was carried out for 7 minutes at a rate of 120 rpm ( at starting ) and 30 rpm ( 3 minutes after starting ). the floc appearance time , the average floc size and the turbidity of treated water at 5 minutes after the stop of stirring were as follows : ______________________________________floc appearance time 30 ( sec ) average floc size 2 . 0 - 5 . 0 ( mm ) turbidity of treated water 0 . 6 ( degree ) ______________________________________ thus , it was confirmed that the flocculant prepared in example 2 and stored for 18 months also has excellent coagulating , capability . ing capability of a flocculant which comprises a polymerized silicic acid solution prepared by a process in which the addition of an alkaline agent for the purpose of adjusting ph was not made , as follows : 100 g of an aqueous solution of &# 34 ; class 3 water glass &# 34 ; of which the concentration of sio 2 was 8 . 6 %, was mixed with 50 g of an &# 34 ; h type &# 34 ; cation exchange resin and stirred for 5 minutes with a magnetic stirrer . 90 g of silicic acid solution having an 8 . 6 % sio 2 concentration , 0 . 14 % na concentration and ph of 9 . 3 , was obtained by removing the cation exchange resin by filtration after the finish of stirring . the obtained solution gelled after about 10 minutes , at a room temperature of 20 ° c . the gel was liquefied by allowing it to stand for 24 hours in a vessel the inside temperature of which was constantly maintained at 60 ° c . the solution of polymerized silicic acid thus obtained had a limiting viscosity of 0 . 23 ( 100 ml / g ) and a mean molecular weight of about 240 , 000 . 100g of a flocculant of which the mol ratio of si : fe was 3 : 1 and the total concentration of effective components ( sio 2 + fe 2 o 3 ) was 10 %, was prepared by adding 10 . 4g of ferric chloride ( fecl 3 . 6h 2 o ) and water to 80 . 6g of the above solution of polymerized silicic acid . the coagulating capability of the flocculant was determined by a jar test . namely , the flocculant was poured into a test water having 100 degrees of turbidity , 60 mg / 1 ( as caco 3 ) of alkalinity and a ph of 7 . 5 prepared by adding kaolin and nahco 3 to distilled water , and stirred . the rate of pouring of the flocculant was 2 . 0mg / 1 and the stirring was carried out for 7 minutes at a rate of 120 rpm ( at the start ) and 30rpm ( at 3 minutes after starting ). the floc appearance time , the average floc size and the turbidity of the treated water were as follows : ______________________________________floc appearance time 30 ( sec ) average floc size 2 . 5 - 5 . 0 ( mm ) water turbidity 0 . 8 ( degree ) ______________________________________ thus , it was confirmed that the flocculant prepared by the above process has excellent coagulating capability . the following test was carried out for the purpose of clarifying the variation of characteristics of the polymerized silicic acid solution when the alkali metal concentration in the solution is varied . 2kg of an aqueous solution of &# 34 ; class 3 water glass &# 34 ;, of which the sio 2 concentration was adjusted to 9 . 0 %, was subjected to treatment to remove alkali metal by mixing it with 3 kg of an &# 34 ; h type &# 34 ; cation exchange resin and stirring for 5 minutes . after removing the cation exchange resin by filtration , 1 . 8 kg of a silicic acid solution having a 9 . 0 % sio 2 concentration and 0 . 01 % na concentration was obtained . the solution was divided into 11 samples . after adding different amounts of sodium hydrate to each sample , their ph , sio 2 concentration and na concentration were determined . the samples were allowed to stand at room temperature of 20 ° c . to determine their gel time . eight samples gelled within 30 minutes and three samples did not gel even after a lapse of 24 hours . both the gels and the solutions which did not gel were further allowed to stand for 24 hours in a vessel the temperature of which was maintained constant at 60 ° c . after the lapse of 24 hours from the start of standing at 60 ° c ., it was observed that the eight gel samples had converted to a liquid and the other three solution samples set to gel . the liquefied samples were analyzed to determine their limiting viscosity and mean molecular weight . the results are shown in table 3 . table 3______________________________________ meansam - sio . sub . 2 na gel time condition limiting mol . ple con . con . at 20 ° c . after 24 hr vis . weightno . (%) (%) ( min .) at 60 ° c . ( 100 ml / g ) ( g / mol ) ______________________________________1 8 . 6 0 . 041 1 solution 0 . 48 6400002 8 . 6 0 . 051 1 solution 0 . 42 5800003 8 . 6 0 . 062 1 solution 0 . 37 5000004 8 . 6 0 . 108 1 solution 0 . 23 2600005 8 . 6 0 . 154 10 solution 0 . 21 2200006 8 . 6 0 . l85 10 solution 0 . 20 2000007 8 . 6 0 . 200 30 solution 0 . 18 1700008 8 . 6 0 . 291 30 solution 0 . 14 900009 8 . 6 0 . 449 not gelled gel -- -- in 24 hr10 8 . 6 0 . 514 not gelled gel -- -- in 24 hr11 8 . 6 0 . 980 not gelled gel -- -- in 24 hr______________________________________ as seen from table 3 , it was observed that the solutions having an na concentration exceeding about 0 . 3 % did not show the characteristic of converting from a gel to a liquid necessary for the present invention . it should be understood that , although the preferred embodiments of the present invention have been described herein in considerable detail , certain modifications , changes , and adaptations can be made by those skilled in the art and that it is hereby intended to cover all modifications , changes and adaptations thereof falling within the scope of the appended claims .