D.P.H,

Lecture and P.-actloal VI,

^dness in Waters0Water which requires an excessive amount of soap to form a

lather, or which forms much incrustation on vessels in which it stands ~r is bea^od, is commonly called a ''hard water ' 0 Hardn* may be thought of as the "soap-destroying property of a water 1.

Calcium and magnesium salts, chiefly the bicarbonates and sulphates are responsible for hardness. Water can have a high total solids content, without; much hardness.

Disadvantages of Hardness.

(1) Domestic and Industrial.

(a) S o ap waste. Soaps are sodium or potassium salts of fatty 3.cids which are soluble, and their '‘cj-eansing" powers depend ..o a large extent upon their ability to form soap layers round particles of ‘dirt". When calcium or magnesium salts are present in the water they react with the soluble Na and K soaps, forming insoluble Ca and Mg soaps, which are useless for cleansing purposes,. Hence it is only after sufficient soluble soao has been added to react with all the Ca and Mg sal^s in a water that any further addition of soap is usefu_.

EiJa - fatty acid + CaS04 ____ v Ca - fatty acid + Na2S04(s^rnblo soap) (soluble) (insoluble srap)

A high degree of hardness can thus result in considerable financial loss to domestic users and also tn laundries.Another disadvantage is that the llme^iaaps tend to stick to fabrics and are hot easily rinsed away0 This causes spots and stains.,

(b) Boiler Scale and Occlusion f Pipes, Boiler scale is caused by the precipitation ‘of Ca and Eg sulphates ("hard scale'; and carbonates ("soft scrC.e") when water is concentrated in abe ilex-. Scale is a poor conductor of heat, which means that financial loss may be incurred by need of excessive fuela The seal© is liable to crack suddenly, which results in uneven heating of the boiler walls, and fatal e xplosion3 have, boon traced to this occurrence„

Continuous passage of heated hard water through pipe-lines may result in scale formation which decreases the diameter of the pipe and increases frictionj this means that higher^ pressure must be applied t o th'i w a t e r * if efficient foow is to be maintained, with resulting economic loss,

(c) Hard water is a disadvantage in various other industries, such as those of canning, textile-finishing, tanning, the fermentation, artificial ice, paper making, sugar-refining, and various other chemical industries*

(2) Health,

Intestinal irregularities ere sometimes considered to be caused by hard waters„ Probably personal idiosyncrasy is a factor hereu

Psychological effe c t are not uncommon. The prestige -f holiday resorts is not enhanced in some minds when the water supply has the reputation of being hard.

A\

- 2-

C. Kinds of Hardness.

(a) Temporary Hardness.

So-called because it can be removed by boiling the water. This results in precipitating bicarbonates of Ca and Mg (which are soluble), as insoluble carbonates.

(b) Permanent Hardness.

This cannot bo removed by boiling, and is for this reason calls d "permanent". It is due to sulphates (and to some extent chlorides) of Ca and Mg.

(c ) Tctal Hardness is the sum of the Temporary and Permanent.

D. Removal of Hardness.

(a) Removal of Temporary, i.e. Bicarbonate Hardness.

This method is obviously impracticable except fn a very small scale, as for occasional domestic purposes.

(ii) By use of lime - CaO

A The Temporary and Permanent Hardnesses are usually removed by a combination of the lime and soda processes. A number of chemical details not mentioned here require close attention, and in practice the calculation of the amounts of the lime and soda-ash required, and the mechanical process of their addition to the water is far from being so simple an operation as the chemical equations above suggest.

Ca(HC03 ) 2 ------- CaC03

(insoluble)

co 2 h 2o

(i) By boiling, e.g. Ca(HC03 )2 ----^ CaC03 + COg + HgO(insoluble)

Mg(HC03 )2 ---- > MgC03 + COg + HgO

(rather insoluble)

CaO added to water forms Ca(0H )2

Then Ca(HC03 ) 2 + 6a(0H )2 -----^ 2CaCC>3 + 2HgO(insoluble)

(ratherinsoluble)

Removal of Permanent Hardness, i,e. Sulphate Hardness.

By use of soda-ash - NagCO^

CaS04 + Na2C03 ------ ^ CaC03 + Na2S04\

(c) »Base-Exchange1 Method «f -removing Hardness.

This process removes both Temporary and Permanent Hardness in ono operation, and by means of one substance. The substance used is one of a large class known as zeolites, which are complex com- pounds ef'Na, Si, A1 and 0. "Permutit" is one such zeolite, and Is the basis of the now well-known domestic water softeners.

All zeolites are insoluble in water, and the reaction of base- exchange occurs at the surfaces of the zeolite particles. lhe exchange is one of Na of "the zeolite for Ca or Mg from bicarbonates and sulphates in the inflowing water which is passed fvgr the zeolite, the outflowing water being free of all hardness.

NagAlgSigOg

(insoluble)

Na2Al2Si208

(insoluble)

The(insoluble) CaAl (insoluble) N a o A ^ S of NaCl

+ Ca(HC03 ) 2 CaAlgSigOg +

(insoluble)

CaSO^ CaAl2Si208

(insoluble)

2NaHC03

(soluble)

NffeSFO 4

(soluble)

(•r MgAlgS^Dg) can m w . b e reconverted Into y passing through if a concentratcd solution

e.g. CaAl2Si208 + 2NaCl — ,— ^ Na2A l 2 S ^ 8 (insoluble) (soluble) (insoluble)

CaCl2 (soluble)

and the zeolite is thus recovered foiv further use.

Determination »f Total. Temporary, and Permanent Hardnesses.

For these determinations, use is made of a standard soap solution, which for convenience is made so that1 cc. = 1 part of ha.rdness = 1 milligram of CaC03, its equivalent.

t / f j W ) \ X I ' *100 cbs^^&^'the water (=*100 grams = 10 milligrams) in any

determination are measured i n t ^ a stoppered bottle, and the soap solution is added from a burette a few ccs. at a time, with vigorous shaking after each addition. When after such shaking a "permanent“ voluminous lather remains in the bottle for 5 minutes, the "end-point11 of the titration has been reached, and the burette is read, [See details under Practical Procedure]

I£ must be remembered that 100 ccs. of distilled water [i.e.,•ne containing no hardness at all] require 1 cc, of the soap solution to f o m a permanent lather, so that in-any titration 100 ccs# of a water containing any hardness, 1 cc, must be deducted from the burette reading.

Total Hardness Determination.

100 ccs. of the water are titrated with soap solution.Suppose 25 ccs. of soap solution were required:-

Then 100 ccs. of water (i.e. 105 milligrams) contain 25-1 = 24milligrams ff Total Hardness

.*, Total Hardness = 24 milligrams per 105 milligrams = 24/105

a '

Permanent Hardness Determination.

Another 100 ccs. of the water are boiled for 15 minutes. This boiling destroys temporary (bicarbonate) hardness, leaving only permanent hardness. After cooling and filtering (from precipitated CaC03 ), the volume is made up again to 100 ccs. with distilled water. A titration by means of soap solution is now made to determine the permanent hardness.

Suppose 100 cos, of the water now required 7 ocs. of soapsolution

Then 100 ccs. of water contain 7-1 * 6 milligrams ofPermanent Hardness

. Permanent Hardness = 6 milligrams per 105 milligrams- 6/105.

The Temporary Hardness is not determined separately by titration, but is equal to 'ilne dif fere"ce between the Total and Permanent Hardnesses

i.eD Temporary Hardness = /Total - Permanent/

= 24/105 - 6 /1 0 5 = 18/105

From these results it is possible to calculate the equivalent quantities of lime cr soda-ash necessary to remove the temporary and permanent hardnesses respectively, or the total hardness bythe sum of the two.

•

A table is given under Practical Prooedure which inoludes the quantities of CaO and UacOOg equivalent to 1 cc. of soap solution (= 1 milligram of CaCOg).

Fe Calculation of the amount of NagCO^ required to remove Permanentbaroness„

From the example gust given, 100 ccs. of the water contain6 milligrams of Permanent Hardness (£ & mgme CaC0„).Now 1 milligram CaCO™ 81 1.06 milligrams NagCOg

. . 100 ccs* of water (or 105 milligrams), require 6 X 1.06 ■ 6.36mgms. of NagCO^.

G-o Calculation of the gmount of CaO required to remove Temporaryhardness.

Although from the soap titration one can ascertain the amountof Temporary Hardness in a wa,terf it is not always permissible to assume that adding an amount of CaO exactly equivalent to it will remove all the Temporary Hardness. This is because most waters contain not only and Mg bicarbonates, but also other soluble bicarbonates (chiefly llaHCOg) whioh although they cause no hardness at all,, nevertheless react with CaO Just as the bicarbonates of1 Ca and’ "Ijg do, and react more quickly with CaO than Ca and Mg bicarbonates0

Furthermore j, the small amount of free COg dissolved in the water will react with CaO instantaneously.

(UJUr < ^ - J - l r » w U < . — ^ *--- g~

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■Tic- — S"- /J

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The following equations illustrate the above: -

Ca(HC03 )2 + Ca(0H) 2 --- > CaC03 + 2H20 ............(1 )Mg(HC03 )2 + Ca(0H ) 2 . y MKCQ3 + 2H20 ............(2)

2NaHC03 + Ca(0H )2 --- ^ Na2C03 +

c o 2 + Ca(0H) 2 ---^ Ca2C03 + H2° ........,...(4 )

It is obvious that to remove the Temporary Hardness, CaO equivalent to all the four reactions above must be added. The total bicarbonates (i.e. of Ca, Mg, and Na) can be determined by titrating 100 ccs. of water with N/50 HC1 using methyl orange, that is by determining the "alkalinity"of the water.

Suppose 100 ccs. of water required 30 ccs. of N/50 HC1

Then 100 ccs. require 30 ccs. of N/50 Ca© = 30 x .56 mgms.CaO

= 16.8 mgms.CaO

The free COq can be determined by titrating 100 ccs. of the water by N/50 NatfH, using phenol phthalein, that is by determining the "acidity" of the water.

Suppose 100 ccs, of water .required 1.2 cc. of N/50 NaOH

Then 100 ccs. of water require a further 1.2 ccs. of N/50 CaO

= 1,2 x .56 mgms.CaO

= 0.672 mgm. CaO

Hence to remove the Temporary Hardness one must Qdd to 100 ccs. of water [1608 + 0.672 mgm, = 17.472mgms.] CaO.

By comparing this amount of CaO required to remove Temporary Hardness with that equivalent to the Temporary Hardness as found by soap estimation, it is seen that a ®ide difference is obtained.The Temporary Hardness was found by soap titration to be 18.0/10°, which would require 18 r .56 = 10.08 mgms. of CaO/lO^, whereas above we see that 17,472 mgms. of Ca0/l05 are required.

Summary of Relationship of Hardness and Alkalinity-Acidlmetry.i

Ca(HC0^)g

Mg(HC03 ) 2

NaHC03

cause Temporary Hardness deter­mined by scap titration

causes no hardnessd

Free (dissolved COp)causes no hardness

cause Alkalinity titrated by N/50 HC1

causes Acidity titrated by N/50 NaOH

All react with CaO

CaSO^ cause Permanent Hardness

MgS04

References to Literature.„

Jameson and Parkinson Thresh and Beale

cause neither Alkalinity nor Acidity

Do not react with CaO, but react with Na2C03

Synopsis of Hygiene,Examination of Waters and Water Supplies,

* S * t k ivix It**' ( 2

F r a c t l c ^ * 4 \1. Find the "oxygen absorbed from permanganate" (or Tidy

Figure) in one hour at laboratory temperature by (a) Tap

Water, (b) Sewage Effluent A.

2. Determine the dissolved oxygen of tap water by~ - f'

Winkler's process. '{* > { c ,

Strrrf \ fLt* VjW Express your result in parts per 100,000 and as

cubic centimetres of gas per litre.

3. Set up a Rideal Stewart test, J.*. "Biochemical

yxygen Demand" test in the sample of sewage effluent A , ,'

/ <j # - *and -complete the second half of the test next time, m v .

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Practloal XI

D.P.H.-------- «r

1, Complete the Rideal Stewart test put up last time

and write a report on the purity of the effluent,%

2. Determine by Wanklyn’s method the free and saline

/^ •» L > irand the albuminoid ammonia content of the Sewage

Effluentc- " * • * A l ; -

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3, Perform qualitative tests for nitrate and nitrite

on the Sewage Effluent C,

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P. P. H .

Practical XII Milk

103/1. Determine the specific gravity, and the percentage of total

solids present in Milk A.

2. Estimate the fat content of Milk A, using Gerber's centri­

fugal method.

3. Examine Milks B and CT with a lactometer. Which of these

would you submit to further analysis? What adulterations,

if any, would you suspect, and what further estimations would

you require to be done?

The Analysis of Water.

A complete water analysis may give evidence on the following,*-

(1 ) the degree of pollution by organic matter - animal andvegetable

(2 ) the amount of hardness and of mineral matter(3) the source of the water(4) the presence of poisonous metals and the capacity of the

water to dissolve poisonous metals. _ LL<aA rT\

Collection of Satiiples.

For a chemical analysis a Winchester quart (half a gallon) is required to be collected in a chemically clean bottle by an experienced sampler and despatched to the laboratory as quickly as possible. The water must be kept cool by enclosing the bottle in a special box lined with felt and which i3 refrigerated by means of an Ice container.

The sample is taken under representative conditions of use: e.g. where a river is to be sampled, a specimen should be obtained from the actual spot whence the water is taken for supply.

Information to be recorded by the Sampler.

The following points should be recorded on the bottle by the sampler and a copy of the information should be kept:-(a) source of the water, (b) geological or geographical data,(c) weather conditions just preceding the sampling, (d) reasen for requiring analysis, (e) any special points, (f) signature of the sampler and of a witness In important cases, (g) date.

Scheme ^f Examination.

A complete report on a water supply would include Information under the following headings:-

Physical Characters:-

(1) Colour(2) Turb idit y(3) Taste and Odour

Microscopical Characters of Sediment. __ , (r O ' * * t Ia m MA,. yr<rr^

Bacteriological Characters.

Chemical Characters. y .

Sanitary Survey: -

(1) Methods of collection(2 ) Methods of storage(3) Methods of handling and distribution.

General Characters.

For example, defects not ascertainable by the ab«ve methods of analysis but which are proved to exist by clinical results, as in the case of the association of goitre and Iodine lack.

rw

- 2 -

Methods employed in the Physical Examination of Water

(1) Colour

Water may be coloured in the presence of clay, algae, excess of iron,- and coloured substances derived from peat. The depth of such' colour is measured by:-

(a) Lovlbond1 s water colorimeter. - in which the colour of a two foot depth of the water is compared with the colour of light transmitted through slips of coloured glass. Each colori­meter is supplied with a range of such coloured glasses, numbered according to the depth of oolour, so that the colour of the water can be expressed in terms of the number of the coloured glass slip which it most elosely matches.

(b) Platinum-cobalt standards- the colour of a certain depth of tbe water is matched against the colour of a solution of a double salt of platinum and cobalt. The colour of the water is expressed In terms of that particular dilution of the salt which represents the closest match,

(2) Turbidity

This is measured by:-

(a) Fuller's earth suspensions - which are prepared in different strengths. The turbidity of a known depth of water is com­pared with the suspensions and the amount expressed in terms of that strength which is most closely matched.

(b) Platinum wire visibility method - This method requires a rod into one end of which is inserted a platinum wire of standard diameter projecting from it at a right angle. The rod is lowered vertically into the water until the wire just ceases to be visible when the depth to which the rod has been lov/ered is measured. The turbidity is then expressed in terms of this distance. (j) I tty-

t f e f ,

(3) Taste and Odour

This can only be assessed In terms of descriptive epithets*'

The degree of aeration and of hardness affects tho taste of a water. Abnormal tastes are caused by:-

Iron in excess, salt in excess, soil, putrid matters, absorbed gases, certain algae, and chlorine.

The Chemical Analysis of Water

All water supplies are more or less polluted with organie matter. Even 'safe1 waters - those which experience has shown not to spread v/ater-borne disease - will on chemical analysis yield evidence of some organic pollution, Xt-J^S— the-degree, and nature pollu­tion which determines, the safety of a supply. The analysis therefore must determine precise figures of the amounts of the substances indicating pollution, which are present, for it is on these figures that an opinion on the safety of a supply is based. The opinion required is not as to whether pollution exists but whether there is dangerous pollution.

The polluting substances are not in themselves harmful t* health hut they act as indicators *f the possible presence of pathogenic frganisms. Bacteriological analysis might then be assumed to be tKe only investigation needed but as a matter of fact chemical analysis is usually indispensible. The chief values and advantages of chemical analysis in comparison with bacteriological examination are these

(1 ) the sampling error is not so great as in bacteriolegicalanalysis

(2) transit errors are not so important(3 ) the analysis can be performed in about three hours(4 ) the technique is not so difficult(5 ) the interpretation of the analysis tends to be m*re precise

^__(6 ) remote pollution «f dangerous character can be revealed bychemical methods even when the bacterial c»unt appears perfectly satisfactory. This is of value in that it reveals a water to be potentially dangerous because the polluting circumstances may reappear

(7) a relatively precise curve of the normal variations,throughout an annual period, of the composition of the water can be i*btained. Abnormal variations for this curve would be o£ great value in indicating the need for special measures to secure the purity of the supply.

(8) chemical methods will give information on (a) the hardness,(b) the presence of poisonous metals, (c) the metal-solvent character, (d) the probable source *f the water.

The following determinations are usually made in a complete chemical water analysis: -

Reaction to litmus *r the precise pH.

Total Solids:- T.S.Volatile Solids V.S.,Non-volatile Solids N.V.S.

Free and saline ammonia F.A.Albuminoid ammonia A.A.Nitrite nitrogen Nitrite N.Nitrate nitrogen Nitrate N. Oxygen absorbed from permanganate orChlorine as chlorides ClTotal Hardness:- T.H.

Permanent Hardness P.H.Temporary Hardness Tp.H.

Poisonous metals P.M.Phosphates PO4Sulphates SO4

A quantitative determination «f these is made except that nitrites, phosphates and sulphates are usually tested for only qualitatively.

The results are expressed as parts per 100,000 in this country and as parts per million in the United States.

At one time the quantities found were recorded as grains per gallon and this is still done by some analysts in expressing the hardness -*f water and the amount of lead dissolved in water. The conversion of *ne scale to the other is easy because a gallon of water weighs 70,000 grains, so:-

parts per 100,000 x 0.7 = parts per 70,000= grains per gallon

and, grains par gallon x = parts per 100,000

Notes on the Test3.

(a) Reaction to litmus.

Test, Take two red. and two blue litmus papers and half immerse them in the water placed in a clean porcelain dish. Leave the papers for 10 minutes before inspection.[Accurate pH measurements are made with the comparator - but are only required for special purposes.]

Interpretation.

(1) Most waters in this country are slightly alkaline because of alkaline salts dissolved from the strata through which or over which the water has passed before collection.

(2) Many surface waters which are derived from peaty surfaces are acld_.because the decay of vegetable matter results in the formation of acids. The importance of this lies in

"Y tlie fact that such waters may be metal-solvent to a dangerous degree. Moorland waters therefore require special precautions in their collection and chemical treatment to prevent the risk of lead poisoning in the consumers.

(3) An acid water must be neutralised before the chloride estimation oan be carried out.

<b> Total Spiids.

Test.(1) A dish capable #f-holding 60 to 70 c. c. (a platinum dish

for accurate work) is carefully cleaned, heated to red­ness, allowed to cool in a desiccator and weighed. It is placed on a water bath.

(2) An accurate measuring flask of 100 or 250 c.c. capacity, depending on the amount of total solids the water 3s likely to contain, is filled with the sample.m

(3) About 50 c.c. of the sample are poured into the dish and when nearly evaporated a further quantity is added until all the measured amount of water is fully evaporated.

(4) The dish is wiped, placed in the hot air oven at 180OC. for an hour, then cooled in a desiccator for ten minutes and reweighed.

The difference in weight will give the total solids in the measured quantity of water.

Example:-

Weight of dish 32.765 gms.

Weight of dish + solids from 250 c.c. of water 32.875 gms.I

' ' ‘ Difference = 0.110 gms.

There are therefore 0.11 gms. T.S* in 250 c.c. of water

But 1 c.c. xf water weighs 1 gm.

. . 0.11 gms. T.S. in 250 gms. of water

. . 0.044 gms. T.S. in 100 gms. of water

i.e. 44 mgms. in 100,000 mgms. of water

or 44 parts per 100,000.

tUA * ^HL. I * / (Ti

The same dish containing the solids is now heated over a nakedBunsen flame and it is very important to note the appearance in the first stages of ignition - whether the solids char or show any other change on ignition. When fully ignited the dish is cooled as before and reweighed.

The loss of weight on ignition will give the amount of volatile solids in the measured quantity of water and the difference Detween'tEe^calculated total solids and volatile solids will equal the non- volatile solids.

Interpretation. Figures of Total Solids.

The following are figures taken from a series of analyses and it is to "be noted that within a group there are wide variations which depend in general on the nature of the strata associated with the particular supply:-

Surface Waters

RiversShallow Wells Deep Wells

3.0 to 12.0 parts per100, 000

3.0 to 40.015.0 to 60.020.0 to 200.0

These figures are illustrative only and do not give the extremes which may actually be found.

(1) The amount of total solids may give a clue as to the source of the water - an upland surface water may give as low a figure as 5 parts per 100,000 whereas a water which has percolated through strata such as the chalk may give a figure of 100 parts or more per 100,000. In an unpolluted water the amount of total solids depends upon the solubility of the strata thr ugh which or over which the waterHhas passed. A high figure of total solids may therefore be found in certain rivers, in deep wells and also in certain dhallow wells: a low figure is found in upland surface waters. It is important to note that the total solid figure is not the same as the total hardness (see Hardness).

(2)The proportion of the total solids which are volatile solids is not of great importance for although a high figure of volatile solids was-, once regarded as indicative of organic pollution it is clear that ignition will bring about volatilization of some of the inorganic constituents of the total solids. The appearance of the total solids and the changes on ignition may be valuable. Excess of iron will colour the residue. If on ignition there is marked dis­colouration, charring or scintillation it is evidence of organic matter in excess.

(3)The total solid residue may be used for the determination of lead or other metals present in so small a quantity as not to be demonstrable or measurable in the unconcentrated water.

Chlorine as Chloride

Test

Before the titration, is performed, the reaction of the water to litmus must''<t>eT^ eiermined. If acid, a little sodium bicarbonate must"be addeatio efxe c t a slightly alkaline reaction, 7/Ith very alkaline waters - those that give an alkaline reaction to phenol phthal«tin - careful n eutralization with dilute sulphuric acid is required.

If the water is.eqlftused, clarification can generally be effected by the addition,of soma freshly precipitated aluminium hydroxide with subsequent filtration.

Waters containing sulphides also require a preliminary treatment and some workers add a f ew crystals of zinc sulphate which procedure permits of a direct titration of such waters.

The process of titration is as follows. Into a clean porcelain dish put 100 c.c. of the wa£ir and then 1 c.c. of a 5 per cent, solution of potassium chromate. From a burette run in a standard solution of silver nitrate which Is of such strength that 1 c.c. s 1 .0 mgm, of chlorine, u n t i l a dirty red colour appears and is permanent. Stir carefully with a glass rod throughout the titration. It is a good plan In order to be certain of the end point to set up a n«nta»ol diflh containing the, same amount of water

fifoyomata by the side of thecLiah in which the determination Is being made.

The end point is not very sharp but for most practical purposes is sufficiently accurate.

The calculation, is:-

say 100 c.c, of the water needed 8.7 c.c, of silver nitrate

. . 100 c.c. of the water contain 8,7 x 1.0 mgms. of chlorineas chloride

fmri as 100 c.c, = 100,000 mgms, therefore chlorine as chloride is 8.7 parts per 100,000.

/

The result Is sometimes also expressed in terms of sodium chloride.

The r ationale of the chloride estimation consists in the pro c ip 1 tat Ion of 1 tKe' .nhl nil'll a' as a 11 YfflT Silver chromatewETch is a red substance is also formed but is decomposed by a chloride In solution. Hence no silver chromate remains undecompoeed as l*ng as any chloride remains to be precipitated. The reactions

“ 0l \

2KN03 W

AgCl

may be represented thus:-

i'TaCl + AgNOg

KgCrO^ + 2AgN 03

Ag2Cr04 + 2NaCl

iXio-TV'—

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AggCrO4 +

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N.B.Free Chlorine. The silver method determines the total amount of

chlorine as chloride and #f any free chlorine which may be present in the water. In a chlorinated water free chlorine is likely to be present. The reagent for free chlorine Is a 0 .1 per cent., solution of ortho-flidine . in 10 .jper cent, hydrochloric acid. One c7c~. is added to 100 c.c. »f the water in a Nessler glass and after mixing the glass is allowed to stand f*r 5 minutes. A perceptible yellow qfllour develops if the water contains as little as 0.02 parts per million of free chlorine. The test can be used quantitatively by comparison of tho colour produced with the colour of standards.

CkS&if standards are prepared by mixing varying proportions of solutionsu * n copper sulphate and potassium bichromate. The strengths of these

2. V ^standard colours in terms of free chlorine colour have been deter­mined and can be found in the larger books on water analysis.

Metals,. Lead is the metal which from tho health viewpoint has most efton to be tested for. The possibility of the presence of copper or zinc has occasionally to be considered*-^- Iron and manganese' if present in quantity may cause unpleasant tastes and discolouration and turbidity *f the water.

Special techniques are used by analysts in tho examination of waters for these and other metals. The following tests are morely indicative of the types of reaction which may be employed.

Tests.

To 5$ c.c. of the water in a porcelain dish or Nessler glass add a few drops of sodium sulphide. The following results may be obtained: -

A s

Lead

Copper - Iron

- black precipitate or discolouration - insoluble inKCN or dilute JEl

„ " " - soluble in KCN" " - soluble in dilute

I _ ' HC1Zinc - white precipitate or dpaioasconaO-on ©ifcrstanding

As confirmatory tests to be performed in a Nessler glass on fresh quantities of the sample:- ■■■

Lead - potassium chromato - yellow precipitate of leadchroma te

Cepper - acidulate, add potassium ferrocyanide - bronzecolouration

Iron - acidulate, add potassium ferrocyanide - blue

-7- a ^ a. colouration£inc - Acidulate, add potassium ferrocyanide - white

precipitate or opalescence

If these tests are negative then the water will have to be con­centrated and the tests repeated in order to confirm the absence or reveal the presence »f minute quantities of these metals.

In the cases #f Pb, Cu and Fe the sulphide colour produced may be used to determine the quantity present by comparing the colour with that produced in a water containing a known quantity of the metal. To a series of 3 dishos add 100 c.c. ff distilled water and graded quan-J 3ay 9*1 * 0,4 c,c* a standard solution (1 c.c, = 0,l«wi„

•f the metal) of the metallic salt. Add the sulphide and compare the dolour produced with that of the sample. If an accurate match cannot be Obtained, a further series of standards must be set up. The amount of metal present is then calculated and expressed as parts per 100,000.

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Practical Exercises.

1. Determine the Total, Permanent, and Temporary Hardnesses of Water (A).

P r a ^ l c a l ^ ^ o c e ^ ^ ^ (A) Total Hardness,

(i) Into a 3toppered "bottle measure 10Q ccs, of the water,

(ii) Run in standard soap solution from a burette, #ne ec, at a time, shaking vigorously, after each addition.

Early in the titration little or no lather will form, but nearer to the end-point a lather will appear. To decide whether it is "permanent *' or not, lay the bottle (steppered) on its side. When the end-point is reached a voluminous lather filling nearly all the space above the water will remain for 6 minutes, and will not disappear on '‘rocking1' the bottle gently, as it will if the end-point has not been quite reached.

Note. Waters containing much magnesium salts give a dirty-grey scum, which must not be mistaken for a lather: the titration must be con­tinued.

(iii)Read the burette; remember to deduct 1 cc, j ~~ ^ ~~ <y '

(iv)Estimate tho Total Hardness in parts per 10®.

(B) Permanent Hardness.

(i) Boil another 100 ccs, of water in a beaker f«r 15 minutes.

(ii) Cool and filter into a 100 ccs, measuring cylinder or graduated flask; make up to 100 ccs. with distilled water.

(iii) Titrato with soap solution; remember to deduct 1 cc

(iv) Estimate the Permanent Hardness in parts per 10®,

(C) Temporary Hardness,

Calculate the Temporary Hardness from the results obtained above,

(D) Calculate from the Permanent Hardness f«und, the number «f milligrams of Na2C03 which must be added to 100 ccs. of the water (i.e. 10® milligrams) to remeve the Permanent Hardness.

See tables at bottom of next page,

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2. Determine the Alkalinity and Aciditv •£ the Water (A), and estimate the amount of lime (CaO) required to remove the Temporary Hardness.

Practical Procedure (A) Determination of Alkalinity.

(i) Measure 100 ccs. of water int#. a flask,

(ii) Add methyl orange.

(iii) Titrate with N/50 HC1 or N/50 HgS04. £ N &

(B) Determination of Acidity.

(i) Measure 100 ccs. *f water into a flask.

(ii)Add phenol phthalein.

(iii)Titrate with N/50 NaOH.

(C) Add the two titrations above, and express as the equivalent of CaO: compare this figure with that o£ tile CaO found to be equivalentto the actual Temporary Hardness as formed by soap titration.

N»_te, The following table of equivalents is useful for reference in all the foregoing exercises:-

1 cc. s#a]D s#iutiwn - lmgm.CaCO^tx 1 mgm.of Hardness] = 1 cc. N/50 CaCOg

= 0,56 mgm. CaO s 1 cc, N/50 CaO

= 1.06 mgm.NagCOj = 1 cc. N/50 NagCOj

= 1 cc. N/50 HC1 = 1 cc, N/50 NaOH

3. Tost water (B) and (C) for the presence of Phosphates and Sulphates.

Procedure for Phosphates

To a test-tube half filled with the water, add about 2 c.cs. of ammonium molybdate: solution, followed by nitric acid, drop by drop untill distinctly acid. 'Now add ammonium molybdate, drop by drop until 15-20 drops have been added. Do not shake. Allow to stand for 15 minutes. In the presence of phosphates, a yellow tinge and turbidity appears near the surface. i f •

Procedure for Sulphates.

To a test-tube half filled with the water, add 2 drops of HC1, f’oJLiowed by a few drops of Baciosolution. A turbidity or a copious

■ y/hite precipitate ensues, according to the amount of sulphatepresent.

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Collection Number: AD843

XUMA, A.B., Papers

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