ARE CHEMISTS GENERALLY PREPARED TO ABANDON CLARK’S METHOD FOR ESTl3IATION O F HARDNESS IN WATERS ?
BY DR. ALBERT13. LEEDS. At the present time, when many chemists retaiii ;ind others h a w laid aside Clark’s method, it is difficult to discover what is signfied by the figures repdrted under hardness i i i ii reported analysis, and it is most desirable t h a t this obscurity sliould be done away with, and a uniformity of practice secured. The objects in TTiew, iu t h e ordinary coilrse of analysis, when hardness is determined, are as follows : 1st. Simply to place the water in the category of hard or soft waters. Usually private individuals desiring water analyses wish to know merely of tlieir fitness for domestic use, and the estimation of the hardness by soap solution is adequate to supply t h e information needed on this point. But inasmnch as the analyst starts with an unknown water, which often turns out to be magnesian in clinracter, or t o owe part of its liurcliiess to other constituents than lime and ni;ignesi;a salts, the time expended in estiniating its hardness, temporary and permanent, by soap, is greater oftentimes thm that deinandetl by other methods. 2d. Soap destroying power. 1 ’ 1 1 ~analyst in his laboratory uses as nearly piire potassium oleqte as he can prepare, and dissolves this doap in a mixture of two volumes of alcohol and one of water. His object is to so adjust his manipulation as to effect ‘cl combination of the lime and magnesia with the oleic acid, aiid to obtain from a table of hardness as near an approach to the actual quantities of these bodies, estimated as calcium carbonate, a s possible.
CLARK'S 31 ETHOD FOR ESTIMATIOK OF HARDSESS IK WATER.
115
T o achieve this result, he frequently has occasion to dilute with distilled water and to manipnlat,e with various refinements having no relation to tlie actual use of soap. For factory use the soad destroying power can best be deteTmined by trial with the particular water and soap used ; for general purposes it can be sufficiently well estimated from the cdciuni carbonate equivalent deduced from titration witli sodium carbonate. Very freqnently soap is used with water as hot as the hand can bear, and the valuable suggcstion 11:~sbeen made by Jlr. Herbert Jackson t h a t on heating to YOo C * the soap test gives the same figui-es as are obtained by means of dilution. Even with this device, the results rai'y widely in many cases from'the true calcium carbonate eqnivalent, wliile they do not necessarily give soapdestroying power. 3d. Boiler incrusting solids-" scale." Hardnees, however determined, should not be used in judging of t11c scale-forming properties, but if clicmists will persist in guessing, as they d o , n t present, the Hehner figurcs allow of s;tfer guess work th:tn those obtained by soup. 4th. Character and anioniit of clicinicals to be added before precipitittion and filtrat8ion of Iiiii,dt)iiiiig :ind scale-forming subst:inces. Ordinarily tliis is eff'cctccl by the addition of lime, soda or soda-ash, singly or combined. X o m tlie Hclincr method in its direct deteriiiinittiori of :dlinlinity bcto;.e :tnd after ersporation with sodium c:irboiiate bears a certziu analogy wit11 the proc2ss of softening. I n pr:ictice a trial should always be made using the calculated miou::ts of rciigeiits, for such is the effect of tlie condition and relative proportions of the s d t s present in water, t h a t agreement betwecii tlie tlieoreticxl and nctn;rl results after treatment is frequeiitly lacking. Still i t is obtiiiiiecl in a fair number of cases, and much more with tlie soda tlinii with the soap titration, Noreover, when soda is employed, the softening as judged by tlie soap test, may be aplxwent (so far as scale is concerned) ratlier than real. TVliat is needed, both as to tcale ant1 i t e preyention, i s a specia.
*
Chem. News, xlix., 149.
1 1 6 CLARK'S METHOD FOR ESTIMATION OF HARDNESS I N TVATER.
technical study having these two objects solely in view. A method followed will be indicated in a subsequent paper. Having stated the objections which led me several years ago to abandon t h e soap test, I desire to give some experiments made a t t h a t time which appeared desirable before taking this step. I n t h e first place are minute variations in the conduct of the test, or of the temperature, etc., sufficient to origiiiate discrepancies between the actual amounts of calcium carbonate equivalent and those given in t h e table of hardness, when the test solution of calcium chloride is employed and the test is performed in the usual manner. T h e experiments were made with potassiuin oleate dissolved in 2: 1 dilute alcohol and of such btrength t h a t 14.25 C.C. produced a permanent lather with 50 c.c. CaCl solution = 20 pts. CaCO, per 100 C.C. COYPdltISOlV WITH ORDINARY TABLE OF HARDNESS. -__ ___
Mgrms. CaCO,
c. c. by Ordinary Table.
0.0 2.0 1.0 4.0
0.70 2.05 3.60 3.60 5.00 6.40 7.80 9.15 11.75 14.25
taken.
6.0
8.0 10.0 12.0 16.0 20.0
-~ -~
c. c . by
Experiment. 1.05 2.15 3.90 3. SO 5.53
6.41 7.90 9.30 11.78 14.25
M rms.
lifferencer CaEO, by inc. c. Experiment. 0.35 0.10 0.30 0.20 0.58 0.01 0.10 0.15 0.03 0.00 _____ -___
(By ClaCI,.)
-
-
Differences Mgrms. CaCO,.
+ + + + + + + -+
0.55 2.21 4.43 4.29 6. SO P.O1 10.15 12.26 16.10 20.00
0.55 0.21 0.13 0.29 f 0.80 0.01 0.15 0.26 0.10 0.00
_-
T h e comparison shows t h a t these discrepancies are practically of no importance. I n t h e second place, is i t desirable to abandon the use of t h e ordinary table, calculated from Clark's Table of Hardness, and,
CLARE’S METHOD FOR ESTIMATION OF HARDKESS IN WATER.
117
following a suggestion of Mr. Wanklyn, to take the equivaleiit of calcium carbonate directly from the soap titre minus a certain correction. For the purpose of this inquiry, I took l . G grms. oleic acid, exactly neutralized with decinormal soda madeup to 300 c.c., and finding solution stronger than theory required, diluted until 50 c. c. water, containing the equivalent in CaCl, of 10 mgrms. CaCO, was exactly equivalentto 1 1 . 4 ~c.. soap 5Oc. c. distilled wster alone was equivalent to 1.4 c. c. soap. T h e results were :
CaCl sol. c. c.
CIICO, Mgrms.
Oleate Calculated.
Oleate Used.
10.0 15.0 20.0 25.0 50.0
4.0 G.0 8.0 10.0 20.0
5.4 7.4 9.4 11.4 21.4
5.40 7.40 0.45 11.40 21.50
Ry deducting 1.4 from the e. c. oleate used, the amount of CaCO, equivalent is obtained directly. Were the continuance of the soap best desirable on other grounds, the testing of this method with calcium and magnesia salts, singly and combined, would havs been further prosecuted. Thirdly, Would another salt of calcium give the same results taken from the Hardness Table, as CaCl, ? A solution of standard CaSO, = 0.200 grm. per titre CttCO,
N was made u p b y a d d i n g 20 c. c. - H,SO, to 5G c. c. CaO solution 10 containing 1 mgrm. per C.C. Different volumes of this solution were made u p to 50 c. c. and titrated with a soitp solution of 14.25 c. c. I 20 mgrm. CaCO, asdetermined with standard solution of CaCl,.
CaSO,= c. C. by CaC0,mgrms' ordinary used.
0.0 2.0 4.0 (i.0 S.0 10.0
16.0 w.0
Table.
1,
'mgrmsCaC0, differences m rms
c c
by
difrrences, by experiment in c experiment
1.0s 2.10 3 . 60
0.33 0.05
5.00 6.40 ;. SO
0.00
11. ;0 14.10
0,02
0.55 2.0s 4.00
0.00 0.00 0.00 0.15
'
'
6.00 3.00
10.00 13.93 19-76
ta80,.
I 0.>2+ ,
0.03 0.00
+
0.00 0.00
1, ::::1
0.24-
h solntion of C h C O , in CO, water was made with the view of holding :is little free C,O, its possshle. 30 e. e. = 20 m g m . Ca CO3=13,i; c. c. soap soltition=lr.97 mgrms. of CaCO, per table. Further experiments showed that distilled water containing increasing amounts of dissolved CO, give corresponding differences from the titre obtained with Carbonic acid free water. F o u r t h . Could a magnesium salt be made to givc results corresponding to tlie equivalent CaCO, as taken from the table? 50 C . C . MgSO, sol. ='30 mgrms. CaCO, was titrated with soap run in 1 c. c. a t a time and with much shaking. It gave 110 s h s f a c t o r y end reaction but ail apparent permaueiit lather a t about 1'3 c. e. instcad of 14.2; e. e. R.:peated w i t h intervals of three minutes between each c. c., an unsntisfactorg end reaction was obtained with 10 to l ? c. c. :?,jc. c. ;\igSO,+35 c. c. water was titred as follows : First : 6 e. c. with 1 c. e . tit 2 minute intervals. 6.7 e. c. a t 5 minnte intervals. 7.1 to 7 . 5 e.?. at 5 minute intervals. c. 1.3 not normal lather : ';.6 iiearly normal. 7.6 t o 7 . 8 e. e. a t three 5 min. intervals. The whole operation required an h o a r and the final result with a iiorrnal lather yielded 7 . 8 c. c . = I o pts. per 100,000. I n anotlier experiment with less time and shaking S.4 c. c. were used,
CLARK’S METHOD F O R ESTIMATION O F HARDNESS I N WATER.
119
and the final outcome shows that with sufficient care and patience a n agreement can be obtained . i n the cttse of magiiesium salt (1 mol, C a O = l mol. MgO) w i t h theoretical figures u p to t h e equivalent of 10 parts C~ICO,pcr 100,000. But a method which necessitates so great :til exp:iiditiiro of time, labor :tnd care to obtain results that only i n ccrtiLiii cases arc approximately correct, should, it ttppoars to me, be abandonctl.
T h e results were as follows : (BY irgso,.)
TABLE O F HARDNESS.
-__ -
2.00 4.00 6.00 8.00 10.00 to. 00 20.00 20.00
--
C.C.
by Table.
c. c. b y di7erences ngrms.CaC0, mxperiment in c. c. iy experiment.
iff erences mgrms.
2.00 3.60 5.00 6.40 7 .so 7 .d o 14.2.5
2.10 3.60 5.03 6. G5 7 . SO s.40 12.00:‘ 10 to 15
O.OS+
14.25
0.10 0.00 0.03 0.26 0.00 0.60
2.08 0.00 6.03 ‘8.35 0.00 10.90
0.00 0.03 + 0.35+ 3.00 0.90+
s
I n conclusioii. I woulcl ask wlietlier the members are prepared to take formal action, ant1 to recommend a rule or practice in estimating and reporting upon what slitlll be conventionally styled the ‘i Temporary ” and ii Permanent ’’ Hardness.
