DRAFT UGANDA STANDARD  
  DUS 289  
Second  Edition  
yyyy -mm-dd 
 
 
 Reference number  
DUS 289: 2022  
© UNBS 2022   
  
Limestone for Industri al use — Specification  
 DUS 289: 2022  
ii © UNBS 2022  – All rights reserved  
 Compliance with this standard does not, of itself confer immunity from legal obligations  
A Uganda Standard does not purport to include all necessary provisions of a contract. Users are 
responsible for its cor rect application  
© UNBS 2022  
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perm ission from UNBS.  
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The Executive Director  
Uganda National Bureau of Standards  
P.O. Box 6329  
Kampala  
Uganda  
Tel: +256 41 4 333 2 50/1/2/3  
Fax: +256 41 4 286 123  
E-mail: info@unbs.go.ug  
Web: www.unbs.go.ug  DUS 289:2022  
© UNBS 2022  – All rights reserved  iii 
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ .............................  v 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Terms and definitions  ................................ ................................ ................................ ...........................  1 
4 Requirements  ................................ ................................ ................................ ................................ .........  1 
4.1  General requirements  ................................ ................................ ................................ ..........................  1 
4.2 Specific requirements  ................................ ................................ ................................ ...........................  1 
5  Packaging  ................................ ................................ ................................ ................................ ...............  2 
6 Labelling  ................................ ................................ ................................ ................................ .................  2 
7 Sampling  ................................ ................................ ................................ ................................ ................  2 
Annex A  (norm ative)   Preparation of main solution  ................................ ................................ .....................  3 
A.1 Reagents  ................................ ................................ ................................ ................................ ................  3 
A.1.1  Dilute Hydrochloric Acid, 1 percent, 40 percent (v/v).  ................................ ................................ ....... 3 
A.1.2  Fusion Mixture  ................................ ................................ ................................ ................................ ....... 3 
A.1.3  Dilute Sulphuric Acid, 1:4 and 1:1 (v/v)  ................................ ................................ ...............................  3 
A.1.4  Hydrofluoric Acid, 40 percent (v/v).  ................................ ................................ ................................ ..... 3 
A.2 Procedure  ................................ ................................ ................................ ................................ ...............  3 
A.2.1  For Other than Magnesite Refractory Materials  ................................ ................................ .................  3 
A.2.2  For Magnesite Refractory Materials  ................................ ................................ ................................ .... 4 
Annex B  (normative)   Determination of Iron by the spectrophotometric method  ................................ ..... 5 
B.1 Outline of the Method  ................................ ................................ ................................ ............................  5 
B.2 Reagent  ................................ ................................ ................................ ................................ ..................  5 
B.3 Procedure  ................................ ................................ ................................ ................................ ...............  5 
B.4 Calibration  ................................ ................................ ................................ ................................ ..............  5 
B.5 Calculation  ................................ ................................ ................................ ................................ .............  6 
Annex C  (normative)   Determination of Manganese  ................................ ................................ .....................  7 
C.1  Outline of the Method ................................ ................................ ................................ ...........................  7 
C.2  Apparatus  ................................ ................................ ................................ ................................ ..............  7 
C.3 Reagents  ................................ ................................ ................................ ................................ ................  7 
C.3.5  Standard Manganese Solution  ................................ ................................ ................................ .............  7 
C.4 Procedure  ................................ ................................ ................................ ................................ ...............  7 
Annex D  (normative)   Determination of phosphorus  ................................ ................................ ....................  9 
D.1  Procedure  ................................ ................................ ................................ ................................ ...............  9 
Annex E  (normative)  Determination of Silica (asSiO2 ) Alumina (as Al2O3) and Ferric oxide (as 
Fe2O3)  ................................ ................................ ................................ ................................ ..................  10 
E.1 Determination of alumina By EDTA method  ................................ ................................ ...........................  10 
E.1.1  Outline of the Method  ................................ ................................ ................................ ..........................  10 
E.1.2  Reagents  ................................ ................................ ................................ ................................ ..............  10 
E.2 Procedure  ................................ ................................ ................................ ................................ ...................  11 
E.2.1 First Titration  ................................ ................................ ................................ ................................ ...........  11 
E.2.2 Second Titration  ................................ ................................ ................................ ................................ ...... 11 
E.3 calculation  ................................ ................................ ................................ ................................ ..................  11 
E.4 Determination of silica by gravimetric method  ................................ ................................ .......................  12 
E.4.1  Reagents  ................................ ................................ ................................ ................................ ..............  12 
E.4.2  Procedure  ................................ ................................ ................................ ................................ .............  12 
Annex F  (normative)   Sampling  ................................ ................................ ................................ ....................  14 DUS 289: 2022  
iv © UNBS 2022  – All rights reserved  
 Limestone shall be first crushed in a jaw crusher, roll crusher or manually using a hammer or 
pounder and a suitable steel plate, until the material in gross sample is of 10 mm size.  ..........  14 
F.1 Reduction by Riffle Divider  ................................ ................................ ................................ ................  15 
F.2 Coning and Quartering Method  ................................ ................................ ................................ .........  15 
F.3 Increment Reduction Method  ................................ ................................ ................................ ............  15 
Bibliography  ................................ ................................ ................................ ................................ .....................  17 
 DUS 289:2022  
© UNBS 2022  – All rights reserved  v 
 Foreword  
Uganda National Bureau of Standards (UNBS) is a parastatal under  the Ministry of Trade , Industry and 
Cooperatives established under Cap 327 , of the Laws of Uganda , as amended .  UNBS is mandated to co -
ordinate the elaboration of standards and is  
(a) a member of International Organisation for Standardisation (ISO) and  
(b) a contact point for the WHO/FAO Codex Alimentarius Commission on Food Standards, and  
(c) the National Enquiry Point on TBT  Agreement  of the World Trade Organisation (WTO).  
The work of preparing Uganda Standards is carried out through Technical Committees. A Techn ical 
Committee is established to deliberate on standards in a given field or area and consists of key stakeholders 
including government, academia, consumer groups, private sector and other interested parties.  
Draft Uganda Standards adopted by the Technica l Committee are widely circulated to stakeholders and the 
general public for comments. The committee reviews the comments before recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council.  
The commit tee responsible for this document is Technical Committee UNBS /TC 301, Chemistry . 
This second edition cancels and replaces the first edition ( US 289:2001), which has been technically revised.  DUS 289: 2022  
vi © UNBS 2022  – All rights reserved  
 Introduction  
Limestone is an important basic raw material for t he chemical industry.  
The chemical industry uses relatively small quantities of limestone as compared to quicklime and hydrated 
lime, although many industries can use both  
Physical requirements, such as specific gravity, porosity, compressive strength and  size of stone are not 
included in this standard, as these requirements will depend on, amongst others, the types of kilns used for 
burning limestone.  
  
  
  
 DRAFT UGANDA STANDARD  DUS 289 : 2022  
 
© UNBS 2022  – All rights reserved  1 
 Limestone for Industri al use — Specification  
1 Scope   
This Draft Uganda standa rd specifies the requirements, test methods and sampling of limestone for industrial  
use.  
This standard does not cover limestone for building, agricultural, metallurgical, glass and ceramic industries . 
2 Normative references   
The following referenced docu ments referred to in the text in such a way that some or all of their content 
constitutes requirements of this document. For dated references, only the edition cited applies. For undated 
references, the latest edition of the referenced document (including any amendments) applies.  
 US EAS 73 , Building limes (quicklime and hydrated lime) — Specification  
3 Terms and definitions   
For the purposes of this document, the following terms and definitions apply  
ISO and IEC maintain terminological databases for use i n standardization at the following addresses:  
— ISO Online browsing platform: available at http://www.iso.org/obp  
3.1 
limestone  
sedimentary rock composed principally of calcium carbonate (calcite) or the double carbo nate of calcium and 
magnesium (dolomite). It is commonly composed of tiny fossils, shell fragments and other fossilized debris  
 
4 Requirements  
4.1  General requirements  
4.1.1 Limestone  for ind ustrial use  shall be in the form of fine or granular powder , free from dirt and other 
foreign matter.  
4.1.2 Limestone for industrial use shall be white in colour  
4.2 Specific requirements  
Limestone shall comply with the requirements given in Table 1 whe n tested according to the test methods 
prescribed in therein .  
2 © UNBS 2022  – All rights reserved  
 Table 1. Specific requirements for limestone for  industrial use  
Characteristic  Requirements   
 Test method  
Loss on ignition, % by mass, max  46.0 US EAS 73: 2000  
Iron as (Fe 2O3), % by mass,  max 0.12 
 Annex B 
Calcium (as CaO), % by mass, min  32 US EAS 73: 2000  
Magnesia as (MgO), % by mass, max  18.4  US EAS 73: 2000  
Manganese (as Mn 2O3), % by mass, 
max 0.01 Annex C 
Phosphorus (as P), % by mass, max  0.001  Annex D 
Silica (asSiO2 ) Alumina (a s Al2O3) 
and Ferric oxide (as Fe2O3)  3 Annex E  
 
 
5  Packaging  
Limeston e shall be packaged in airtight or moisture  proof containers/packages that will protect the product’s 
integrity during transportation, storage and handling . 
6 Labelling  
6.1 When supplied in packages , each package shall be marked indelibly with the fo llowing information:  
a) Name of product  as limestone  
b) Name and physical address of manufacturer  & trade mark  if any;  
c) Net weight in grams  
d) batch number; and  
e) Date of  manufacture . 
f) Best before  date 
6.2 When supplied in bulk, a metallic or cardboard label of appropriate size bearing the above informat ion 
printed with suitable paint or ink shall be conspicuously displayed on the carrier and also placed inside.  
7 Sampling  
Sampling  shall be done in accordance with annex F 
  
 DUS 289: 2022  
© UNBS 2022  – All rights reserved  3 
 Annex A  
(normative ) 
 
 Preparation of main solution  
A.1 Reagents  
A.1.1  Dilute Hydrochloric Acid, 1 percent, 40 percent (v/v).  
A.1.2  Fusion Mixture  
Mix carbonates of sodium and potassium in equal proportion.  
A.1.3 Dilute Sulp huric Acid, 1:4 and 1 :1 (v/v) 
A.1.4 Hydrofluoric Acid, 40 percent ( v/v). 
A.2 Procedure  
A.2.1  For Other than Magnesite Refractory Materials  
A.2.1.1   Weigh accurately 2.5 g of the test sample into a beaker or a porcelain dish and add to it 4 0 to 50 
ml of dilute hydrochloric acid, covering the beaker by means of a suitable cover glass immediately after 
addition of the acid. As soon as effervescence stops, wash the lower surface of the cover glass into the 
beaker and set the contents for drying  and baking at 110oC to 115°C.  
A.2.1.2   After baking for about 20 to 25 minutes, cool to room temperature, add 25 to 30 ml dilute 
hydrochloric acid (40 percent) boil and filter.  
A.2.1.3   Transfer thoroughly the residue in the beaker as well as that adher ing to the sides of the beaker 
to the filter, by hot water. Wash with hot dilute hydrochloric acid (1 percent) and then with hot water.  
A.2.1.4   Wash the filter free from chlorides by means of hot water. Collect the filtrate and washings in the 
same beake r and preserve it (A).  
A.2.1.5   Transfer the filter paper with its residue into a previously heated platinum crucible and char at 
low temperature. Finally ignite at 900oC to 950°C and cool.  
A.2.1.6   Fuse the residue in the platinum crucible with about 3 g of fusion mixture. Cool and extract the 
melt in about 50 ml of dilute hydrochloric acid (40 percent).  
A.2.1.7   Mix with the filtrate from A .2.1.1 and repeat the process of drying and baking.  
A.2.1.8   Extract the baked mass with about 30 to 40 ml of dilut e hydrochloric acid and filter. Transfer all 
the silica in the beaker to the filter thoroughly by means of hot water.  
A.2.1.9   Wash silica on the filter free from chlorides by means of hot water. Collect the filtrate and 
washings in the same beaker and pr eserve the filtrate (B).  
A.2.1.10  Transfer the filter with its residue into a previously weighed platinum crucible and char the filter 
paper at a low heat without burning the paper. Finally ignite at 900oC to 950°C to a constant mass. Moisten  
4 © UNBS 2022  – All rights reserved  
 the residue w ith few millilitres of dilute sulphuric acid (1:1) and add to it about 10 ml of hydrofluoric acid. 
Evaporate to dryness. Ignite and cool.  
A.2.1.11  Fuse thoroughly the residue A .2.1.10 left over in the platinum crucible, after volatization of silica 
with 1 to 2 g of fusion mixture and add the extract in dilute hydrochloric acid to the tiltrate reserved under 
A.2.1.9.  
A.2.1.12  Mix these combined filtrates with that reserved under  A.2.1.4 . Transfer the final flltrate to 250 ml 
volumetric flask and make up to the main solution volume. (If filtrate is bulky, it should be concentrated to 250 
ml by boiling). Suitable aliquots are taken for determination of ferric oxide, alumina, calcium oxide and 
magnesia.  
A.2.2 For Magnesite Refractory Materials  
A.2.2.1 Weigh one  gram of the sample in a Platinum crucible and fuse it with 6 to 8 g of pure anhydrous 
sodium carbonate. Extract the melt carefully with 40 to 50 ml of dilute hydrochloric acid in a 500 ml beaker and 
when dissolution is complete, wash the crucible thorough ly with hot water. Evaporate the solution to dryness 
on hot plate and bake for about 20 minutes.  
A.2.2.2  Cool the beaker; add 25 to 30 ml of dilute hydrochloric acid, boil and filter. Transfer thoroughly all 
the residue in the beaker to the filter by a jet  of hot water and wash it free from acid by means of hot water. 
Collect the filtrate and washings in the same beaker and preserve it. Further, complete the estimation as 
descri bed under A.2.1.5  to A.2.1.12  
 
 DUS 289: 2022  
© UNBS 2022  – All rights reserved  5 
   
Annex B  
(normative ) 
 
 Determination of Iron by the spectrophotometric method  
B.1 Outline  of the Method  
Iron (III) in the aliquot from the main  solution  is reduced to iron (II) with hydroxylamine  hydrochloride and 
treated with  0-phenantharoline. The coloured complex  produced is measured at 510 nm. The amount  of iron 
(as Fe 2O3) is evaluated from the  calibration curve obtained under similar  conditions.  
B.2 Reagent  
B.2.1 Para-nitrophenol Indicator Solution,  1percent.  
B.2.2 Tartaric Acid Solution, 10 percent (m/v ). 
B.2.3 Dilute Ammonia Solution, 1 :3 (v/v). 
B.2.4 Dilute Hydrochloric Acid, 1 :1 (v/v).  
B.2.5 Hydro xylamine Hydrochloric, 10 percent  (m/v). 
B.2.6 Standard Iron Solution ( 1 ml = O.0001 g  of Fe 2O3). 
Dissolve 0.7024 g of ferrous ammonium sulphate  in water, add 5  mI of concentrated H 2SO 4 and oxidize with 
bromine water. Boil to expel excess  bromine. Cool an d make up to 1litre. 
B.3 Procedure  
B.3.1 Take 100 ml of sample into 250 -ml volumetric flask.  
B.3.2 Add few  drops of paranitrophenol indicator and 25 ml  of tartaric acid solution.  
B.3.3 Neutral ize the  solution with ammonia solution.  
B.3.4 Acidify the  solution with dilute hydrochloric acid to pH  4.0 to 4.5.  
B.3.5 Add 20 ml of hydroxylamine  hydrochloride and 25 ml of 0 -phenthroline and  make up.  
B.3.6 Allow to stand for 1 h and measure  the absorbance at 510 nm against reagent blank  prepared by 
using s ame quantity of reagents as  used for sample.  
B.4 Calibration  
Draw a dalibration curve by taking 0, 10, 20, 30, 40 and 50 ml of standard iron solution into six 250 ml 
volumetric flasks and proceed in accordance with B.3 and measure the absorbance at 510 nm  against 
reagent blank. Plot the absorbance values against mg of Fe 2O3 per 250 ml of the solution.   
6 © UNBS 2022  – All rights reserved  
 B.5 Calculation  
Convert the spectrophotometric readings of sample to mg of Fe 2O3 by means of calibration curve and 
calculate Fe 2O3 as follows:  
Fe2O3, percen t by mass =    
 
where  
A  Is mass in mg, of Fe 2O3 found in aliquot of the sample solution, and  
B Is mass in g, of sample represented by the aliquot taken.  
  
  DUS 289: 2022  
© UNBS 2022  – All rights reserved  7 
 Annex C  
(normative ) 
 
 Determination of Manganese  
C.1  Outline of the Method  
Manganese is dete rmined colorimetrically by visual comparison.  
C.2  Apparatus  
C.2.1 Platinum Crucible  
C.2.2 Kessler Cy linders - 100 ml capacity  
C.3 Reagents  
C.3.1  Dilute Nitric Acid - 1:1 (v/v ). 
C.3.2  Sodium Carbonate  
C.3.3  Dilute Phosphoric Acid - 1:1 (v/v). 
C.3.4  Potassium Periodate - solid.  
C.3.5 Standard Manganese Solution  
Dissolve  0.1 g of pure electrolytic  grade of manganese in dilute nitric acid, boil off nitrous fumes and make  up 
the volume to 1 000 ml mark in a volumetric flask. One millilitr e of thi s solution is equivalent to 0.1 mg of 
manganese (as Mn ). 
C.4 Procedure  
C.4.1 Weigh accurately about 1 g of the material and  dissolve in about 25 ml  of dilute nitric acid.  
C.4.2 Filter and wash the residue  with hot water.  
C.4.3 Ignite the residue in a platinum crucible, fuse with  a little sodium carbonate, dissolve in dilute nitric 
acid and add to the main  filtrate.  
C.4.4 To the solution ( if necessary, filtered ) add 20 ml of dilute  phosphoric acid and 0.6 to 0.8 g of 
potassium periodate.  
C.4.5 Heat the solution  to boiling and keep at boiling point for about 10 minutes ( one hour for  very small 
amounts). Cool the solution to room temperature. Transfer  the solution completely to a Ne ssler cylinder and 
make up the volume to  100 ml mark.  
C.4.6 Simulta neously take 20 ml of dilute phosphoric acid and  0.6 to 0.8 g of potassium periodate  in another 
beaker and add 4.2 ml of  standard manganese solution.   
8 © UNBS 2022  – All rights reserved  
 C.4.7 Heat the solution and boil as above.  
C.4.8 Cool and transfer to another Nes sler cylinder and mak e up the volume  to 100 mI. 
C.4.9 The material shall be deemed to ha ve passed the requirement of the  test if the colour produced in the 
test with the material is equal to or less  than that produc ed in the control test.  
 
  DUS 289: 2022  
© UNBS 2022  – All rights reserved  9 
 Annex D  
(normative ) 
 
 Determination  of phosphorus  
D.1  Procedure  
D.1.1 Dissolve 2 g of the material in 20 ml of dilute hydrochloric acid 1:1 (v/v) with a few drops of 
concentrated nitric acid.  
D.1.2 Filter and transfer the filtrate to a 250 -ml measuring flask and make up to the mark.  
D.1.3 Take aliquot equivalent to 0.05 to 0.10 g of the sample in a 500 ml conical flask. Neutralize with 10 
percent sodium hydroxide solution and add 2 to 3 ml excess of concentrated hydrochloric acid. Make the 
volume to about 120 ml by adding water. Add 1  g of citric acid; heat to boiling and add from a burette in thin 
stream, 20 ml of quinoline hydrochloride solution. Put a rubber stopper and shake vigorously for about 5 
minutes. Allow the precipitate to settle down and the solution to cool.  
D.1.4 Filter  under suction through a thick pad of filter pulp prepared on a perforated disc in a funnel. Wash 
the precipitate and the flask w ith water till free from acid ( about 10 ml of the washing and 4 drops of the 
indicator should show colour change from violet t o yellow with 1 drop of 0.1 N sodium hydroxide solution ). 
Transfer the pad of filter paper back with the precipitate to the original flask. Add 50 to 60 ml of water and then 
add 0.1 N sodium hydroxide solution with stirring in multiples of 25 ml from a pi pette till the precipitate 
dissolves completely. Add 5 to 6 drops of the indicator solution and titrate the excess of alkali with standard 
hydrochloric acid until violet colour changes to yellow. The end point is sharp.  
D.1.5 Run a blank determination wit h the same quantity of sodium hydroxide solution which was added in 
the test and titrate with standard hydrochloric acid using 5 to 6 drops of indicator solution.  
D.1.6 Calculation  
Phosphorus (as P ), percent by mass  =  
 
Where,  
V1 volume in ml of standar d hydrochloric acid required for the blank test,  
V2  volume in ml of standard hydrochloric acid required for the sample  
N  normality of standard hydrochloric acid,  and 
M mass in g of the material taken for the test.  
 
  
10 © UNBS 2022  – All rights reserved  
 Annex E  
(normative)  
 
Determination of Silica (asSiO2 ) Alumina (a s Al2O3) and Ferric oxide (as 
Fe2O3)  
  
 
E.1 Determination of alumina By EDTA method   
E.1.1  Outline of the Method  
A suitable aliquo t of the main solution  (Annex A)  is taken in a beaker and 0.05 m EDTA is added in  excess. 
pH is adjusted at 5.8 when EDTA will  form complex with mix ed oxides i. e R 2O2 (Al2O3, F2O3,TiO 2) percent in 
the soluti on. In the first titration,  excess EDTA is titrated  against standard zinc acetate solution using  xylenol 
orange as indicator. Same solution is  boiled with sodium fluoride when EDTA  complexed with alumina is 
released and  titrated agains t standard zinc acetate solu tion. Alumina can be determined from the second  
titration. If titanium is present in the sample,  equivalent amount of EDTA corresponding to  titanium is deducted 
from the second titration  and the remaining quantity of EDTA will  correspond to alumina.  
E.1.2 Reagents  
E.1.2.1 Xylenol Orange (0. 5 percent)  
Dissolve 0.5 g of xylenol orange in 100 ml  water. Add 2 drops of dilute hydrochloric acid  (1:1). 
E.1.2.2 Methyl Orange  
Dissolve 0.05 g of indicator in 100 ml water.  
E.1.2.3 EDTA (0. 05M)  . 
Dissolve 18.613 g of disodium dihydrogen ethylenediammetetra acetate in one litre of  water.  
E.1.2.4 Zinc Acetate Solution  
Dissolve 27.4  g of zinc acetate in 200 ml of water, add 1. 3 ml of glacial acetic acid and 73  ml of sodium 
acetate buffer and make th e volume to 2.5 litres.  
E.1.2.4.1 Standardization of zinc acetate solution  
Transfer, 20 ml of standard EDTA solution (E.2.3) in 250 ml beaker and add 15 ml buffer.  
Titrate agai nst zinc acetate solution using xylenol as indicator until the color  changes  from yellow to red.  
Calculate t he normality of zinc acetate as follows:  
N=     
  
Where   DUS 289: 2022  
© UNBS 2022  – All rights reserved  11 
 V  is the volume of zinc acetate in ml.  
E.1.2.5  Ammonia Solution. 1 : 1 ( v/v) 
E.1.2.6  Bugler Solution pH ( 5.8 )  
Dissolve 43 g of sodium acetate in 500 ml of  distilled wat er, and 2 ml of glacial acetic acid  and make the 
volume to one litre.  
E.1.2.7 Sodium Fluoride - Solid  
E.2 Procedure  
E.2.1 First Titration  
Take suitable  aliquot say 25 or 50 ml of the main solution in 250 ml beaker and  add 20 ml of EDTA ( 0.05 hf.). 
Stir we ll. Add 1  to 2 drops of methyl orange indicator. Add  ammonia soIution (1:1 ) until just alkaline. Add  15 ml 
of buffer solution and boil for about 5 to  10 minutes. Cool, add about 3 to 4 drops of  xylenol orange indicator 
and titrate with  standard zinc-acetat e solution till colo ur changes from yellow to red.  
E.2.2 Second Titration  
Add about 2 g of sodium fluoride i n the above solution (G.3.1) and boil for 5 to 10 minutes,  cool and add 15 ml 
of buffer solution. Add  about 2 -3 drops of xylenol orange indicator  and titrate against standard iinc acetate  
solution, till colour changes from yellow to red.  
Note the volume ( v) of zinc acetate used.  
E.3 calcula tion 
Aluminium oxide ( Al2O3), percent by mass =  
 
where  
V volume of zinc acetate in ml, required  to titrate  liberated EDTA, calculated  from second titration (G .3.2); 
and 
m mass in g, of the sample taken.  
NOTE - In case tit anium is present, calculate the Al2O3, content as follows:  
Aluminium oxide ( Al2O3), percent by mass  =  
 
where  
v1 volume in ml, of EDTA equiv alent to the  percent by mass of titanium dioxide ( TiO 2) in the sample.   
12 © UNBS 2022  – All rights reserved  
 E.4 Determination of silica by gravimetric method  
E.4.1  Reagents  
E.4.1.1 Dilute Hydrochloric Acid. 40 percent (v/v).  
E.4.1.2 Fusion Mixture  
Mix carbonates of sodium and potassium in eq ual proportion.  
E.4.1.3  Dilute Sulphuric Acid, I: 4 and 1:1 (v/v)  
E.4.1.4 Hydrofluoric Acid, 40 percent (v/v)  
E.4.2 Procedure  
E.4.2.1 Weigh accurately 1.0 g of the test sample into a beaker or a porcelain dish and add to it 40 to 50 
ml of dilute hydrochlo ric acid.  
E.4.2.2 Cover the beaker by means of a suitable cover glass immediately after the addition of the acid. As 
soon as effervescence stops, wash the lower surface of the cover glass into the beaker and set contents for 
drying and baking at 110” to 1 15°C.  
E.4.2.3 After baking for about 20 to 25 minutes, cool to room temperature, add 25 to 30 ml of dilute 
hydrochloric acid, boil and filter.  
E.4.2.4 Thoroughly transfer all the residue as well as that adhering to the sides of the beaker, to the filter 
by hot water. Wash the residue free from chlorides by means of hot water. Collect the filtrate and washings in 
the same beaker and preserve it.  
E.4.2.5 Transfer the filter with its residue into a previously heated platinum crucible and char at low 
tempera ture. Finally ignite at 900” to 950°C and cool  
E.4.2.6 Fuse the residue in the platinum crucible with about 3 g of fusion mixture. Cool and extract the 
melt in about 50 ml of dilute hydrochloric acid.  
E.4.2.7 Mix with the filtrate preserved under B.2.1 an d repeat the process of drying and baking. Extract 
the baked mass with about 30 to 40 ml of dilute hydrochloric acid and filter.  
E.4.2.8 Transfer all the silica in the beaker to the filter thoroughly by means of hot water. Wash silica on 
the filter free f rom chloride by means of hot water. Collect the filtrate and washings in the same beaker and 
preserve the filtrate.  
E.4.2.9 Transfer the filter with its residue into a platinum crucible and smoke off the filter paper at a low 
heat without burning the paper . Finally ignite at 900oC to 950°C to a constant mass. Moisten the residue with 
few millilitres of dilute sulphuric acid (1:1) and add to it about 10 ml of hydrofluoric acid. Evaporate to dryness, 
ignite, cool and weigh.  
E.4.2.10  Carry out a blank determin ation following the procedure specified in A.2.1 to A.2.9 using the same 
amount of reagents but without the sample.  
E.4.2.11  Calculation  
Silica, expressed in percent by mass, shall calculated using the formula below  
 DUS 289: 2022  
© UNBS 2022  – All rights reserved  13 
 where  
A  is the mass in grams of plati num crucible with residue of silica before hydrofluorization;  
B is the mass in grams of platinum crucible with residue obtained after repeated hydrofluorization;  
C is the mass in grams of silica obtained in blank determination, and  
D is the mass in grams o f the sample taken.  
  
  
  
14 © UNBS 2022  – All rights reserved  
 Annex F  
(normative)  
  
Sampling  
Limestone shall be first crushed in a jaw crusher, roll crusher or manually using a hammer or pounder and a 
suitable steel plate, until the material in gross sample is of 10 mm size.  
The material sh all be mixed well and reduced to 20 kg, which shall then be further processed in stages as 
detailed in Fig, 2.  
For reduction at various stages, one of the methods detailed in H.1 to H.3 shall be followed . The mass of the 
each laboratory sample shall be at  least 200 g.  
 
  
 DUS 289: 2022  
© UNBS 2022  – All rights reserved  15 
  F.1 Reduction by  Riffle Divider  
After each crushing, the material shall  be well mixed and poured into the riffle. This process shall be repeated  
using rifles of different sizes according to the size of the crushed material.  
F.2 Coning and Quartering Method  
In this method, the crushed sample shall be well mixed and then scooped into a cone -shaped pile. Care  shall 
be taken to drop each scoopful over the same spot to ensure even  distribution of lumps and fines on all sides 
of the cone.  
After the cone is formed,  it shall be flattened by pressing the top of  the cone with the smooth surface of the 
scoop. Then, it is cut into quarters  by two lines which intersect at right angle at the Centre of the base of the  
cone. The bulk of the sample is re duced to half by rejecting any two  diagonally opposite quarters.  
F.3 Increment Reduction Method  
 The division of the gross sample  (after being crushed to ) 10 mm) by the manual increment division method 
(see Fig. 3 ) shall be carried out a ccording to the fo llowing procedure. It is advisable to have at least 20 
increments under this method.   The size of the increment shall be as specified in Table 2 . 
a) Spread the crushed sample on a smooth, flat and non -moisture absorbing plate, into a uniform flat 
rectangle  of dimensions a x b mm.  
b) Divide the rectangle into five equal parts lengthwise and four  equal parts breadthwise (for 20 increments ) 
as given in Fig. 3.  
 
 
c) From each of the 20 parts so obtained, equal quantities, not less  than that specified in Table 3, shall be 
collected with the help of  a suitable scoop and combined together to form the reduced  sample.  In the 
above procedure, the scoop shall be inserted to the bottom of  the sample layer and if necessary, a 
bumper plate may be inserted in front  of the  scoop to facilitate the operation.   
16 © UNBS 2022  – All rights reserved  
 Table 2 — Size of increments in manual increment division method  
Size of limestone, mm  Thickness of layer, mm  Quantity to be obtained at one 
time from each part, g  
10 30 – 40 250 
4.75 25 – 35 150 
1.70 15 – 25 40 
0.85 10 – 20 25 
0.15 5 – 10 5 
 
 
  DUS 289: 2022  
© UNBS 2022  – All rights reserved  17 
 Bibliography  
 
[1] IS 574:1970, glassy sodium metaphosphate — specification  
[2] US 289: 2001, Specification for Limestone for chemical industries  
[3] IS 3204:1974, Specification for limestone for chemical industry — specific ation  
[3] IS 1760:1962, Methods of chemical analysis of limestone, dolomite and allied materials.  
[4] IS 2109:1962, Methods of sampling dolomite, limestone and other allied materials  
 
 DUS 289: 2022  
© UNBS 2022  – All rights reserved  19 
 Certification marking  
Products that conform to Uganda standards may be  marked with Uganda National Bureau of Standards 
(UNBS) Certification Mark shown in the figure below.  
The use of the UNBS Certification Mark is governed by the Standards Act, and the Regulations made 
thereunder. This mark can be used only by those license d under the certification mark scheme operated by 
the Uganda National Bureau of Standards and in conjunction with the relevant Uganda Standard. The 
presence of this mark on a product or in relation to a product is an assurance that the goods comply with th e 
requirements of that standard under a system of supervision, control and testing in accordance with the 
certification mark scheme of the Uganda National Bureau of Standards. UNBS marked products are 
continually checked by UNBS for conformity to that stan dard.  
Further particulars of the terms and conditions of licensing may be obtained from the Director, Uganda 
National Bureau of Standards.  
 
 DUS 289: 2022    
 
ICS 91.100.10  
Price based on nn pages  
© UNBS 2022 – All rights reserved