PUBLIC REVIEW DRAFT DRAFT UGANDA STANDARD  
  DUS ARS 1492  
First  Edition  
2021-mm-dd 
 
 Reference number  
DUS ARS 1492 : 2020 
© UNBS 20 21 
   
Agricultural liming materials — Specification  
 PUBLIC REVIEW DRAFTDUS ARS  1492: 2020  
ii                © UNBS  2021 - All rights reserved  
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 PUBLIC REVIEW DRAFTDUS ARS  1492: 2020  
© UNBS  2021 - All rights reserved                 iii National 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  
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The work of preparing Uganda Standards is carried out through Technical Committees. A Technical 
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Draft Uganda Standards adopted by the Technical Committee are widely circulated to stakeholders and the 
general public for comments. The committee reviews the comments befor e recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council.  
This Draft Uganda Standard, DUS ARS  1492: 2020 , Agricultural liming materials — Specification , is identical 
with and has been reproduced from an African  Standard , ARS 1492: 2020 , Agricultural liming materials — 
Specification , and adopted  as a Uganda Standard.  
The committee responsible for this document is Technical Committee UNBS/TC 2, Food and agriculture , 
Subcommittee SC 20, Agrochemicals  and veterinary drugs . 
Wherever the words, “ African Standard " appear, they should be replaced by "Uganda Standard."  PUBLIC REVIEW DRAFTAFRICAN 
STANDARD ARS  
1492  
First Edition 2020 
 
 Reference No. ARS 1492:20 20(E) 
ICS 65.080  
 
 
© ARSO 20 20 
 
 
 
 
  
 
  
 
 
 
Agricultural liming materials — Specification 
 
 
 
  
 
  
 
  
 
  
 
  
 
 
 
 PUBLIC REVIEW DRAFTARS 1492:20 20 
ii © ARSO 20 20 — All rights reserved  
Table of contents  
 
1 Scope  ............................................................................................................................................. 1  
2 Normative references  ..................................................................................................................... 1  
3 Terms and definitions  ..................................................................................................................... 1  
4 Requirements  ................................................................................................................................. 2  
4.1 Chemical composition  ............................................................................................................ 2  
4.2 Requirements for agricultural limestone  ................................................................................ 2  
4.3 Sieve analysis classifications for agricultural slag  ................................................................. 3  
4.4 Requirement for hydrated lime and burnt lime  ...................................................................... 4  
4.5 Heavy metal contaminants  .................................................................................................... 4  
5 Sampling  ......................................................................................................................................... 5  
6 Compliance  ..................................................................................................................................... 5  
7 Packaging and labelling  ................................................................................................................. 5  
7.1 Packaging  .............................................................................................................................. 5  
7.2 Labelling ................................................................................................................................. 5  
8 Material safety  ................................................................................................................................ 6  
Annex A (normative)  Determination of calcium carbonate equivalent (neutralizing value)  ................... 7  
Annex B (normative)  Determination of moisture content  ....................................................................... 8  
Annex C (normative)  Determination of available lime index  .................................................................. 9  
Annex D (normative)  Determination of magnesium oxide content  ...................................................... 11 
Bibliography  .......................................................................................................................................... 13 
 
  PUBLIC REVIEW DRAFTARS 1492:20 20 
© ARSO 20 20 — All rights reserved iii Foreword 
 
The African Organization for Standardization (ARSO ) is an African intergovernmental organization 
established by the United Nations Economic Commission for Africa (UNECA) and the Organization of 
African Unity (AU)  in 1977. One of the fundamental mandates of ARSO is to develop and harmoniz e 
African Standards (ARS) for the purpose of enhancing Africa’s internal trading capacity, increase Africa’s product and service competitiveness globally and uplift the welfare of African communities. The work of preparing African  Standards is normally carried out through ARSO  technical committees. Each 
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work.   ARSO  Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.  
 
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Attention is drawn to the possibility that some of the elements of this document may be the subject of 
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This African Standard was prepared by the ARSO Technical Harmonization Committee Number 5 on Chemistry and Chemical Engineering (ARSO/THC 05).  
  
 
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    PUBLIC REVIEW DRAFTARS 1492:20 20 
© ARSO 20 20 — All rights reserved v Introduction 
 
At a global scale, soils are increasingly being degraded and becoming marginal for agricultural 
production driven by e.g. salinization, erosion and acidification (FAO, 2015) . Soil acidi fication  is one of 
the most prevalent problems in production of food and fibre because at least 40%, and by some estimates as much as 70%, of the world’s arable land is affected  (Rengel, 2003) . With increased 
pressure to produce more food for the expanding population of this planet and with urbanization claiming large chunks of arable land, agriculture is pushed more and more into marginal land plagued with edaphic and other stresses, including acidity.  The major processes leading to soil acidification 
include (1) net H
+ excre tion by plant roots due to excess uptake of cations over anions; (2) removal of 
alkalinity in farm biomass  products such as grain, hay, meat, and wool  which increases as yields 
increase; (3) accumulation of organic anions in the form of soil organic matter; (4) mineralization of organic matter, nitrification of ammonium, and subsequent leaching of nitrate, and (5) input of acidifying substances such as NH
4+-based fertilizers  and urea, elemental S fertilizer and the growth of legumes  
(Rengel, 2003; Goulding, 2016; Holland et al ., 2019) . 
 
Crop growth is often limited in tropical acid soils through a number of factors, including low pH per se, toxicities of aluminium (Al) and manganese (Mn), and deficiencies of phosphorus (P), calcium (Ca), magnesium (Mg) or molybdenum (Mo) (Blamey et al., 1989) . At 8.1 %, aluminium is the most abundant 
metal and the third most common element in the earth's crust  after oxygen  (46.6 %)  and silicon (27.7 
%). At mildly acidic or neutral soil pH values, Al is primarily in the form of insoluble aluminosilicates or 
oxides.  The principal adverse effects of acidity on soil fertility occur at soil pH values below 5.5 due to 
acid dissolution of alumin ium (Al) and the onset of Al phytotoxicity that affect root (and plant) growth 
(Wong et al., 2003) . Thus, Al toxicity is the major growth- limiting factor for crop cultivation on acid soils. 
The initial and most dramatic symptom of Al toxicity is inhibition of root elongation, which can occur 
within 1 -2 hrs after exposure to Al.  This results in reduced volume of soil explored by the root system 
and direct interference with uptake of ions such as calcium and phosphate across the cell membrane 
of damaged roots  (Kochian, 1995). These phytotoxic effects are unimportant in moderately acidic soils 
with pH values of 5.5 to 6.5 when the concentration of toxic forms of Al is normally negligible. 
Manganese toxicity and deficiencies of phosphorus, calcium, and magnesium are common in acidic 
soils. Soil nutrient deficiencies exacerbate the problem of inefficient nutrient uptake due to restricted 
root growth and root damage (Sumner et al., 1991). In drier environments, poor water use due to poor 
root development is considered to be another adverse effect of Al phytotoxicity.  
 Liming is a common agricultural practice worldwide, used for  increasing productivity in acid agricultural 
soils (Bolan et al., 2003; Fageria et al., 2011; Paradelo et al., 2015) . Lime requirements of crops grown 
on acid soils are determined by the quality of liming material, status of soil fertility, crop species and cultivar within species, crop management practices, and economic considerations. Soil pH, base saturation, and alumini um saturation are important acidity indices that are used to determine liming. 
Liming  improves soil pH, Ca, and Mg contents and reduces Al concentrations in the soil solution. In 
addition, liming improves beneficial microbe populations in the soil. Furthermore, liming improves P concentration in the soil solution by reducing P immobilizati on by Fe and Al in acid soils  (Fageria et al., 
2008) . All these beneficial effects of liming improve the root growth of crop plants.  Liming has also been 
shown to increase the soil organic carbon (SOC) with resultant increase in crop yields (Paradelo et al., 2015)  while at the same time immobilizing cadmium in the soil, thus reducing its uptake by crops and 
improving the safety and quality of food crops (Shi et al., 2019) . Liming enhances the physical, chemical 
and biological properties of soil through its direct effect on the amelioration of soil acidity and its indirect effect on the mobilization of plant nutrients, immobilization of toxic heavy metals, and improvements in 
soil structure and hydraulic conductivity ( K
s) (Bolan et al ., 2003) . 
 
A range of liming materials are available, which vary in their ability to neutralize the acidity. These include calcit ic limestone (CaCO
3), burnt lime (quicklime) (CaO), slaked/hydrated lime (Ca(OH) 2), 
dolomit ic limestone  (CaMg(CO 3)2), slag (CaSiO 3), marl/ marlstone, shells, magnesian limestone, 
marine limestone, chalk  and other materials (Bolan  et al., 2003). The amount of liming material required 
to rectify soil acidity depends on the neutralizing value of the liming material and pH buffering capacity of the soil.  
 PUBLIC REVIEW DRAFTPUBLIC REVIEW DRAFTARS 1492:20 20 
© ARSO 20 20 — All rights reserved  1  
Agricultural liming materials — Specification 
  
1 Scope  
 
This African Standard specifies the requirements and methods of sampling and tests for agricultural 
liming materials.  
 
2 Normative references  
 The following referenced documents are indispensable for the application 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.  
 
EN 12048, Solid fertilizers and liming materials — Determination of moisture content — Gravimetric 
method by drying at 105
±2 °C 
 ISO 7409, Fertilizers — Marking — Presentation and declarations  
 ISO 8157, Fertilizers and soil conditioners — Vocabulary  
 ISO 8397, Solid fertilizers and soil conditioners — Test sieving  
 ISO 11047,  Soil quality — Determination of cadmium, chromium, cobalt, copper, lead, manganese, 
nickel and zinc — Flame  and electrothermal atomic absorption spectrometric methods  
 ISO 11465, Soil quality — Determination of dry matter and water content on a mass basis — Gravimetric 
method  
 
ISO 14820- 1, Fertilizers and liming materials — Sampling and sample preparation — Part 1: Sampling 
 
ISO 14820- 2, Fertilizers and liming materials — Sampling and sample preparation — Part 2: Sample 
preparation  
 ISO 17318, Fertilizers and soil conditioners — Determination of arsenic, cadmium, chromium, lead and 
mercury contents  
 
3 Terms and d efinitions  
 For the purpose of this standard, the terms and definitions in ISO 8157 and the following apply . 
 3.1 
agricultural liming m aterial  
a product whose calcium and magnesium compounds are capable of neutralizing soil acidity  
 3.2 
blast -furnace slag  
the non- metallic product, consisting essentially of silicates and aluminosilicates of calcium and other 
bases, that is developed in a molten condition simultaneously  with iron in a blast furnace  
 3.3 
blast -furnace slag, air- cooled  
the material resulting from  solidification of molten blast -furnace slag under atmospheric  conditions; 
subsequent cooling may be accelerated by application of water to the solidified surface  
   
AFRICAN STANDARD  PUBLIC REVIEW DRAFTARS 1492:20 20 
2 © ARSO 20 20 — All rights reserved 3.4 
blast -furnace slag, granulated  
the glassy, granular material  formed when molten blast -furnace slag is rapidly chilled,  as by immersion 
in water  
 
3.5 
burnt lime  (quick lime)  
a material, made from limestone which consists essentially of calcium oxide or combination of calcium 
oxide with magnesium oxide  3.6 
calcium carbonate equivalent (C.C.E.)  
the acid  neutralizing capacity (of an agricultural liming material) of the material expressed as weight 
percent of calcium carbonate  
 3.7 
fineness  
the percentage by weight of the material which will pass sieves of specified sizes  
 3.8 
hydrated lime  
a material, made from lime, which consists essentially of calcium hydroxide or a combination of calcium hydroxide with magnesium oxide and/or magnesium hydroxide  
 3.9 
limestone  
a material consisting essentially of calcium carbonate or a combination of calcium carbonate with magnesium carbonate capable of neutralizing soil acidity  
 
4 Requirements  
 
4.1 Chemical composition  
 Agricultural liming materials shall be classified in terms of calcium carbonate equivalent (C.C.E) as shown in Table 1.  
 
Table 1 — Agricultural liming materials requirements  
 
No. Material  minimum Calcium carbonate 
equivalent (CCE), %   Test method  
i) Quicklime  140 Annex A  
ii) Hydrated lime 110  
iii) Limestone 80  
iv) Slag 80  
v) Shells  80  
 
NOTE  Marl and some by -product liming materials are used for neutralizing soil acidity, but due to their varying composition, 
their chemical limits are not included. In some economic circumstances limestone, slag, and shells of less than 80 % C.C.E. m ay 
be used.  
 
4.2 Requirements for agricultural limestone  
 
4.2.1  Sieve analysis classifications for a gricultural limestone  
 The sieve analysis shall be done in accordance with ISO  8397. Agricultural limestone shall be classified 
according to the  minimum percentage passing the no. 8(2.36- mm) and no. 60( 0.25m m) as shown in 
Table 2. 
 PUBLIC REVIEW DRAFTARS 1492:20 20 
© ARSO 20 20 — All rights reserved  3 Table 2 — Sieve analysis classification for agricultural limestone  
 
Sl/no  Class 
designation  Passing no. 8(2.36 mm) sieve, 
min per cent  Passing no. 60( 0.25mm ) 
sieve, min, per cent  
i S 100 100 
ii T 99 75 
iii O 95 55 
iv N 90 40 
v E 80 25 
 
NOTE  1 These classifications apply where the agricultural limestone is obtained by the normal crushing procedure and the 
product contains the fines of fracture. In some economic circumstances, coarser products are used. The No. 60 ( 0.25mm ) sieve 
was selected because research has shown that this sieve gives a more accurate representation of the particle size distributio n 
of most agricultural limestones presently produced than a finer or coarser sieve. The No. 8 (2.36-mm) sieve is used to cont rol the 
upper limit on the amount of coarse limestone particles that may be in the product.  
 
NOTE  2 The relationship between increasing limestone fineness and reactivity is caused by having a larger surface area 
exposed to chemical reaction. The surface area of liming material increases proportionately with decreasing particle size, for 
example, the exposed area of a cube of 1 cm is 6 cm2: decreasing the particle size to 2 mm (10 mesh), or 0.05 mm (300 mesh) 
increases the exposed area to 30 and 1200 cm2, respectively.  
 
4.2.2  Neutralizing requirements for calcitic limestone  
 Calcite shall comply with the neutralizing requirement in Table 3.  
 
Table 3 — Requirements for calcitic limestone  
 
Characteristics  Grade I  Grade II  Method of test  
i) Calcium Carbonate Equivalent (C CE), %, min  70 50 Annex A  
ii) Active lime (total available as CaCO3 + MgCO
3), %, min  50 40 Annex C 
iii) Magnesium,  (as MgO ) %, max  10 10 Annex D  
iv) Moisture content, %, max  10 12 Annex B  
 
NOTE  Another factor which influences the efficiency of a limestone is its neutralizing capacity. This is determined by reacting 
limestone with strong acids, either hydrochloric or sulphuric acid. The limestone’s neutralizing capacity is expressed as a 
percentage value of pure calcium carbonate, which has a neutralizing value of 100%. Commercial limestones may have 
neutralizing capacities greater or lesser than pure CaCO3. Dolomitic limestone (a mixture of magnesium and calcium carbonates ) 
has a theoretical neutralizing value of 108%. Generally, limestones have neutralizing values below 100%. Impurities such as 
clays in limestone reduce their relative neutralizing capacities.  
 To determine the agricultural value (A.V.) of limestones, the particle size efficiency rating (E.R.) has to be adjusted by the neutralizing value (N.V.) ( synonymous  with neutralizing capacity), plus an adjustment for limestone moisture content (M.C.). For 
example, a limestone having an efficiency rating (E.R.) of 85%, a neutralizing value (N.V.) of 95%, and a moi sture content of 
(M.C.) 13%, has an agricultural value of:  
 
AV  =  85% (E.R.) X 0.95 (N.V.) X [1.00 – 0.13 M.C.]  
AV  =  70.25%  
 
4.3 Sieve analysis classifications for agricultural slag  
 
4.3.1  Air-cooled blast -furnace slag  
 
Air-cooled blast -furnace slag shall be classified the same as agricultural limestone as in Clause 4.2.  
   PUBLIC REVIEW DRAFTARS 1492:20 20 
4 © ARSO 20 20 — All rights reserved 4.3.2  Granulated blast -furnace slag  
 
Granulated blast -furnace slag shall be classified in accordance with the minimum percentages passing 
the No. 8 (2.36- mm) and the No. 60 ( 0.25mm) sieves.  
 
4.4 Requirement for hydrated lime and burnt lime  
 
4.4.1  Fineness  
 Hydrated lime and quicklime for agricultural use shall be classified in accordance with the minimum percentages passing the No. 8 (2.36- mm) and No. 60 ( 0.25mm) sieves, as follows:  
 
Table 4 — Particle size requirements for hydrated lime and quicklime  
 
Passing sieve No.  Min. %   Test method  
Hydrated lime  Quick lime   
8(2.36 mm)  100 95 ISO 8397  
60(0.25mm)  97 35 ISO 8397  
 4.4.2  Neutralizing requirements of hydrated lime and quicklime  
 Hydrated lime and burnt lime shall comply with the requirement in T able 5.  
 
Table 5 — Requirements for hydrated lime and burnt lime as soil conditioners  
 
S/N Characteristics  Grade I  Grade II  Method of test 
i) Calcium Carbonate Equivalent (C CE), %, min  85 70 Annex A  
ii) Active lime (available as , Ca(HO) 2,  %, m/m, 
min  60 50 Annex C  
iii) Moisture content, %, m/m, max  10 12 Annex B  
 4.4.3  Neutralizing requirements for dolomite  
 Dolomite shall comply with the requirements in Table 6.  
 
Table 6 — Requirements for dolomitic limestone  
 
S/N Characteristics  Grade I  Grade II  Method of test 
i) Calcium Carbonate Equivalent (C CE), %, 
min 100 70 Annex A  
ii) Total magnesia lime (MgCO 3), %, min  35 10 To be provided  
iii) Moisture content, %, max  10 12 Annex B  
  
4.5 Heavy metal contaminants 
 The heavy metal contaminants, if present, shall not exceed the limits stipulated in Table 7.  
  PUBLIC REVIEW DRAFTARS 1492:20 20 
© ARSO 20 20 — All rights reserved  5 Table 7— Limits for heavy metals contaminants  for agricultural liming materials  
 
S/N Properties  Maximum limits  (mg/kg, dry 
weight)   Test method  
i) Arsenic (As)  10  ISO 17318  
ii) Zinc (Zn) 5  ISO 11047  
iii) Lead (Pb)  30  ISO 17318/ISO 11047  
iv) Copper (Cu)  300  ISO 11047  
v) Chromium (Cr)  150  ISO 17318/ ISO 11047  
vi) Nickel (Ni)  50  ISO 11047  
vii) Mercury (Hg)  2  ISO 17318  
viii) Cadmium (Cd)  5  ISO 17318/ ISO 11047  
 
5 Sampling  
 
Sampling and sample preparation for inspection and testing shall be carried out in accordance with ISO 14820 parts 1 and 2 . 
 
6 Compliance  
 The lot shall be deemed to comply with the standard if after inspection and testing it complies with the 
requirements of this standard.  
 
7 Packaging and labelling 
 
7.1 Packaging 
 
The agricultural liming material s shall be packed in clean, non- defective and strong packages . The 
material for which the package is made shall be such as to protect the contents from moisture and also 
not lead to easy rupture during handling, transportation and storage.  
 
7.2 Labelling  
 7.2.1 Each package of the agricultural liming material shall be legibly and indelibly marked with the 
following particulars:  
 a) Name of product as agricultural liming materials,  
 b) Types  (such as Calcite, Dolomite, Hydrated lime or Burnt lime. ) 
 
c) Grade : such as Grade I or Grade II  
 
d) Elemental calcium and magnesium  percentage by weig ht 
 e) Calcium Carbonate Equivalent (CCE ) 
 f) net weight  
 g) Effective Neutralizing Value (ENV) 
 h) Lot  number or batch number  
 i) Name and  physical address of the manufacturer  
 j) Instructions for use  and handing  PUBLIC REVIEW DRAFTARS 1492:20 20 
6 © ARSO 20 20 — All rights reserved  
k) Storage  conditions  
 l) date of manufacture and best before or expiry date  
 m) Country of origin  
 7.2.2 Bulk containers  
 Where the a gricultural liming materials  is distributed in bulk, the marking information shall accompany 
the delivery note to the purchaser.
 
 
8 Material safety  
 
Each Consignment  shall be accompanied by a Material Safety Data Sheet (MSDS) and a Certificate of 
Analysis (COA) . 
 
 PUBLIC REVIEW DRAFTARS 1492:20 20 
© ARSO 20 20 — All rights reserved  7 Annex A  
(normative)  
 
Determination of calcium carbonate equivalent (neutralizing value ) 
 
 
A.1 Coverage  
 
The calcium carbonate equivalence (CCE) test  is used to determine the neutralizing capability of a 
calcareous  material and to report this value in terms of percent calcium carbonate equivalents (% 
CaCO 3). 
 
A.2 Significance and u se 
 
Calcareous materials such as  crushed limestone, hydrated lime and pulverized slags (from the 
production of steel) have been used extensively as soil  modifiers or agricultural liming materials. A 
measure of their  neutralizing capability can be determined through the use of  this method of test.  Not 
all neutralizing components of a  calcareous  material may be beneficial, therefore, the chemical  analysis 
is suggested.  
 A.3 Apparatus  
 A.3.1  pH Metre.  
 A.3.2  Mechanical Stirrer.  
 A.3.3  Sieve, No. 60 (250- μm). 
 A.2 Reagents  
 A.2.1 Standard hydrochloric acid  — 0. 5 N. 
 A.2.2 Standard Sodium Hydroxide Solution — 0. 5 N. 
 A.2.3 Phenolphthalein Indicator Solution — Dissolve 0 .1 g of  phenolphthalein in 60 ml of rectified 
spirit and dilute with water to 100 ml.  A.3 Procedure  
 A.3.1 Weigh accurately about 0. 5 g of the previously ground  sample to pass through 250 µm sieve,  in 
a 250- ml stoppered conical flask. Add 40 ml of standard hydrochloric acid, with swirling.  Heat to gentle 
boiling, agitating continuously. Boil for 5 minutes and then cool to room temperature. Titrate against 
standard sodium hydroxide solution using 2 to 3 drops of phenolphthalein indicator.  
 A.3.1.1 Carry out a blank test us ing the same quantities of all reagents  but without adding the sample.  
 
A.3.2 Calculation  
 
Neutralizing value (as CaC O3), percent by mass  = 5(𝐵𝐵−𝐴𝐴 )×𝑁𝑁
𝑀𝑀 
 where  
 
B = volume in ml of standard sodium hydroxide solution used in the blank determination,  
A = volume in ml of standard sodium hydroxide solution used with the sample,  
N = normality of standard sodium hydroxide solution, and  
M = mass in g of the sample taken for the test.  
 PUBLIC REVIEW DRAFTARS 1492:20 20 
8 © ARSO 20 20 — All rights reserved Annex B  
(normative)  
 
Determination of moisture content  
 
 
B.1 Procedure  
 
Weigh accurately 2 g of the powdered sample in a platinum or  silica dish. Place It in an Oven maintained 
at 105° ± 2°C, until on  cooling in a desiccator and weighing, constant mass (± 2 m g) is obtained. 
Calculate the percent moisture m the sample.  
B.2 Calculation  
 
Moisture, percent by mass = 100(𝑀𝑀2−𝑀𝑀2)
𝑀𝑀2−𝑀𝑀 
 
where  
M1 = mass III g of the moisture dish with the material before drying,  
 
M2 = mass in g of the moisture dish with the material after  drying, and  
 
M = mass in g of the empty moisture dish.  
 
 
  PUBLIC REVIEW DRAFTARS 1492:20 20 
© ARSO 20 20 — All rights reserved  9 Annex C 
(normative)  
 
Determination of available lime index  
 
 
C.1 Scope  
 
The available lime index of high- calcium quicklime and hydrated lime designates those constituents that 
enter into the reaction under the conditions of this specified test method, otherwise known as the “rapid sugar test method.” The interpretation of results obtained by this test method shall be restricted by this definition.  
 C.2 Summary of Test Method  
 The sample is slaked and dispersed with water. The lime is solubilized by reaction with sugar to form calcium sucrate which is then determined by titration against standard acid using phenolphthalein as the indicator.  
 C.3 Reagents  
 C.3.1  Hydrochloric Acid, Standard (1.000 N)  — Prepare a solution by diluting 83 mL of HCl to 1 L 
with CO
2-free water.  
 C.3.2  Phenolphthalein Indicator (4 %) — Dissolve 4 g of  dry phenolphthalein in 100 mL of 95 % 
alcohol.  
 C.3.3  Sucrose Solution — (40 g of pure cane sugar in solid  form may be used per sample in place 
of a sugar solution.)  Prepare a 40 % solution (w/v) using pure cane sugar and CO
2-free water in a large 
beaker and stir until dissolved. Add several drops of phenolphthalein indicator solution. Add 0.1 N  NaOH 
solution dropwise with stirring until a faint pink colour persists. Stock solution of sugar may be made for 
convenience;  however, it should not be stored for more than two days. As an alternative the acidity of 
each lot of sugar can be determined,  and a correction applied to the titration.  
 C.4 Procedure  
 C.4.1  Procedure for q uicklime  
 C.4.1.1  The sample as received at the laboratory shall be thoroughly mixed and a representative 
sample with minimum weight of 100 g shall be taken and pulverized to pass a No. 50 sieve for analysis. 
Weigh rapidly 2.804 g of the finely pulverized sample, brush carefully into a 500- mL Erlenmeyer  flask 
containing about 40 mL of CO
2-free water, and immediately stopper the flask.  
 
NOTE  Water should not be added to the sample because, especially  with quicklime, there is a tendency for the material to 
cake and form  lumps difficult to completely dissolve in the sugar solution later. On the  other hand, if the lime is added to a little 
water, a better dispersion of the fine particles occurs, leading to a more rapid dissolution of the sample. It  is possible that in the 
case of quicklime, some slaking action occurs to  facilitate the dispersion and solution.  
 
C.4.1.2  Remove the stopper. Place the flask on a hot plate and immediately add 50 mL of boiling CO 2-
free water to the flask. Swirl the flask and boil actively 1 min for complete slaking. Remove from the hot 
plate, stopper the flask loosely,  and place in a cold- water bath to cool to room temperature.  
 
C.4.1.3  Add 100 mL of the neutralized sugar solution (or  approximately 40 g of pure cane sugar). 
Stopper the flask,  swirl, and let s tand for 15 min to react. (Reaction time should  not be less than 10 min 
nor more than 20 min.) Swirl at 5- min intervals during reaction. Remove stopper, add 4 to 5 drops of  4 
% phenolphthalein indicator solution and wash down the stopper and sides of the f lask with CO 2-free 
water.  
 PUBLIC REVIEW DRAFTARS 1492:20 20 
10 © ARSO 20 20 — All rights reserved C.4.1.4  When titrating, first add about 90 %  of the acid requirement from a 100- mL buret. Finish the  
titration, more carefully at approximately one drop per second,  to the first disappearance of the pink 
colour, which persists fo r 3 s. Note the endpoint and ignore any further return of colo ur. 
 
NOTE  A mechanical stirrer may be used during the titration if  desired. Put a clean magnetic stirrer bar into the flask and place 
the flask  on the magnetic stirrer. Adjust to stir as rapidly as possible without  incurring any loss by spattering. Unless the operator 
is familiar with  previous analyses of the lime under test, and in cases where the available lime content varies to extremes, it is 
good practice to run a preliminary test  by slow titration to determine the proper amount of acid required to neutralize the sample.  
 
C.4.2 Procedure for h ydrated l ime 
 The procedure for  determining Ca(OH)
2 is the same as for CaO with the exception that cold CO 2-free 
water is used and the boiling and cooling steps are omitted.  
 C.5 Calculation  
 
C.5.1  Calculate for CaO as follows:  
 
Available lime CaO , % = 𝑁𝑁×𝑉𝑉×2.804
𝑊𝑊 
 
where:  
 
N  = normality of acid solution,  
 
V  = standard HCl used (1.000 N), mL,  
 W  = weight of sample, g, and 2.804 = CaO, g, equivalent to 1 mL of standard acid × 100 
or 1 mL of standard HCl = 1 %  CaO if exactly 2.804 g of sample is used.  
  C.5.2  Calculate for Ca(OH)
2 as follows:  
 
Available lime [Ca( OH)2, % = 𝑁𝑁×𝑉𝑉×3.704
𝑊𝑊 
 
where:  
 
N  = normality of acid solution,  
 V  = standard HCl (1.000 N), mL,  
 
W  = weight of sample, g, and  
 
3.704  = Ca(OH)
2, g, equivalent to 1 mL of standard acid × 100 or 1 mL of standard HCl = 1.32 
% Ca(OH)2 when exactly 2.804 g of sample is used.  
 
  PUBLIC REVIEW DRAFTARS 1492:20 20 
© ARSO 20 20 — All rights reserved  11 Annex D 
(normative)  
 
Determination of magnesium oxide  content  
 
 
D.1 Scope  
 
Magnesium oxide in lime and limestone may  vary from a few tenths to 2 % for high- calcium limestone 
to as  much as 22 % for dolomitic limestone. The pyrophosphate  gravimetric method has been used 
successfully throughout the  industry to determine magnesium within this wide range.  
 
D.2 Summary of t est m ethod 
 
In this test method, magnesium is doubly precipitated as magnesium ammonium phosphate  from the 
filtrate after removal of calcium. The precipitate  is ignited and weighed as magnesium pyrophosphate 
(Mg 2P2O7). The MgO equivalent is then calculated.  
 
D.3 Reagents  
 
D.3.1  Ammonium Phosphate, Dibasic Solution (250 g/L)  — Dissolve 250 g of dibasic ammonium 
phosphate ((NH 4)2HPO 4) in 1 L of water.  
 
D.3.2  Ammonium Hydroxide Wash Solution (5 + 95)  — Dilute 50 mL of NH 4OH with 950 mL of water 
and add 1 or 2 mL of HNO 3. 
 
D.4 Procedure  
 D.4.1  Add 2 drops of methyl red indicator to the combined filtrates from the determination of calcium, 
acidify with HCl,  and concentrate to about 250 mL. Add to this solution about 10 mL of the (NH
4)2HPO 4 
solution, 250 g/L, and cool the solution to room temperature. Add NH 4OH slowly while stirring  constantly 
until the solution is alkaline or the crystalline magnesium ammonium phosphate begins to form; then 
add about 15 to 20 mL of NH 4OH in excess and continue stirring for several more minutes. Allow the 
beaker and precipitate to stand in a cool place overnight. Filter and wash with cold dilute ammonium 
hydrox ide wash solution (5 + 95).  
 D.4.2  Dissolve the precipitate with hot diluted HCl (1 + 9)  and wash the filter paper well with hot diluted 
HCl (1 + 99).  Dilute the solution to 100 mL, cool to room temperature, and  add 1 mL of the 20 % solution 
of (NH
4)2HPO 4. Precipitate the magnesium ammonium phosphate as before and allow to stand for 
about 2 h in a cool place.  
 D.4.3  Filter the precipitate on paper or in a tared Gooch crucible, washing with diluted NH
4OH (5 + 
95). If filtered  through a Gooch, place directly in a muffle at 400 °C and raise heat to 1100 °C. If filtration 
was through paper, place paper and precipitate in a weighed platinum or porcelain crucible. Slowly  char 
the paper without inflaming and carefully burn off the resulting carbon ( Warning! Extreme caution 
should be exercised during this ignition. Reduction of the phosphate precipitate can result if carbon is 
in contact with it at high temperatures.  There is also a danger of occluding carbon in the  precipitate if 
ignition is too rapid.). Ignite at 1100 °C for  ½ h, cool in desiccator, and weigh as Mg 2P2O7. 
 
NOTE  For research purposes or in the most exacting types of work,  the manganese content of the pyrophosphate residue 
should be determined and deducted as Mn 2P2O7. 
 
18.5 Calculation  
 Calculate the percentage of MgO to the  nearest 0.01 % as follows:  
 
MgO, %  = 𝐴𝐴×36.2
𝐵𝐵 
 where:  PUBLIC REVIEW DRAFTARS 1492:20 20 
12 © ARSO 20 20 — All rights reserved A  = Mg 2P2O7, g, 
 
B  = sample, g, and  
 
36.2  = molecular ratio of 2MgO to Mg 2P2O7 × 100. 
 
 
 
 PUBLIC REVIEW DRAFTARS 1492:20 20 
© ARSO 20 20 — All rights reserved  13 Bibliography  
 
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Sumner, Malcolm E., Fey, M. V. and Noble, Alan David (1991), Nutrient Status and Toxicity Problems 
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