CDC 7  (13) DTZS  
 
 
 
 
 
© TBS 2020                  First Edition 2020  
  DRAFT TANZANIA STANDARD  
 
 
 
 
 
 
 
 
Sodium Sul fate, Anhydrous  – Specification  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
TANZANIA BUREAU OF STANDARDS  
 
 
 
 
  CDC 7  (13) DTZS  
2 
 Introduction  
 
Sodium sulfate  (Na2SO 4) is the sodium salt of  sulfuric acid . It is a white crystalline solid also 
known as the  mineral thenardite , while the decahydrate Na 2SO 4.10H 2O has been known 
as Glauber’s salt or mirabilis.  Na2SO 4.7H 2O is transformed to mirabilite when it is cooled. 
Mirabilite is the natural mineral form of the decahydrate.  It is also produced from by -products 
of chemical processes such as hydrochloric acid production.  
 
There are two types of sodium sulfate natural and by product, also known as synthetic.  
i. Natural sodium sulfate is produced from naturally occurring brines and  crystalline 
deposits . It is also found as a constituent of saline lakes   
ii. . Synthetic sodium sulfate is recovered as a by-product  of various manufacturing 
processes.  
Both types of sodium sulfate  have several important and useful applications in various 
consumer products.  
 
Some of the industrial application of Sodium sulfate  are: 
• Used to dry organic liquids.  
• As a filler in powdered home laundry detergents.  
• As a fining agent which removes small air bubbles from molten glass.  
• For defrosting windows, in carpet fresheners, starch manufacture, as an additive to 
animal  feed.  
• In the manufacture of detergents and in the Kraft process of paper pulping.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 CDC 7 (13)  CD 2  
 
©TBS 2020 – All rights reserved                                                                                              3  
Foreword  
 
This Draft Tanzania Standard is being developed by the Industrial and Laboratory Chemicals 
Technical Committee under supervision of the Chemical Division Standards Committee and it 
is in accordance with the procedures of the Bureau.  
 
In the preparation of this Tanzania Standard assistance has been drawn from:  
 
IS 255:1982  (Reaffirmed 2006) Specification for Sodium sulphate, anhydrous,  
published  by Bureau of Indian  Standards . 
 
Acknowledgement is hereby made for the assistance derived from th is source.  
 
In reporting the result of a test or analysis made in accordance with this Tanzania Standard, if 
the final value, observed or calculated is to be rounded off, it shall be done in accordance with 
TZS 4 rounding  off numerical values.    CDC 7  (13) DTZS  
 
 
©TBS 2020 – All rights reserved                                                                                                   
                                                                                                                                           
 DRAFT TANZANIA STANDARD                                                                          CDC 7  (13) DTZS  
 
 
Sodium Sulphate, anhydrous  – Specification  
 
 
1 Scope  
 
This Draft Tanzania standard prescribes the requirements , sampling and test methods for sodium 
sulfate, anhydrous.  
 
2 Normative references  
The following referenced documents are indispensable for the application of this document. The 
latest edition of the refer enced document (including any amendments) applies;  
TZS 59 Water for analytical laboratory use – Specification and test method  
 
3 Terms and definitions  
<<<<<Not applicable>>>>>  
 
4 Requirements  
 
4.1 General requirements  
 
The material shall consist essentially of sodium sul fate, anhydrous. It shall be in the form of white, free -
flowing powder,  free from v isible impurities and shall be completely soluble in water.  
4.2 Specific requirements  
The material, dried in accordance w ith the method given in A -2.1, shall comply with the  requirements given 
in Table 1. when tested  according to the methods prescribed in Annex  A.  
 
 
Table 1 Specific requirements for Sodium Sul fate, Anhydrous . 
 
S/N Characteristic  Requirement (on dry basis)  Method of test  as 
referred to clause 
No. in annex A  
i.  Sodiu m sulphate (as Na 2SO 4), 
percent by mass, min  98.0  A-3 
ii.  Matter insoluble in water,  
percent by mass, max  0.5 A-4 
iii.  Chlorides (as NaCI), percent by mass, max  2.0 A-5 
iv.  Iron, Aluminium and Chromium  
(as R 2O3), percent by mass, max  0.02 A-6 
v.  lron (as Fe), percent by mass, max  0.002  A-7 
vi.  Loss on ignition, percent by mass, max  1.0 A-8 
vii.  pH (of 10 percent solution)  7.0 – 8.0  A-9 
    
 NOTE: from (i) to (v)  carried out on dry basis.  
 
5 Packing and Marking  
 
5.1 Packaging  
The material  shall be supplied in clean, dry and air tight containers, without faults , made of material s 
which do not  affect the contents. The method of closing the containers shall prevent the contents from 
contamination and evaporation.  
 
 
  
2 
 5.2 Marking  
Each container shall bear the following information given in visible , legible and durable marking  in 
English and/or Kiswahili : 
a) Name of the material  
b) Manufacturer’s name  and address  
c) Country of origin  
d) Recognized trade mark, if any  
e) Batch /Lot number  
f) Manufacturing date  
 
6. Sampling  
The procedure for drawing representative samples of  the material and  the criteria for conformity shall 
be as prescribed in  Annex  B. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
©TBS 2020 – All rights reserved                                                                                              3  
 
 
 
Annex A 
(normative)  
 
Analysis of sodium sulphate, anhydrous  
 
A-1. Quality of reagents  
Unless specified otherwise, analytical/reagent grade  chemicals a nd water for analytical laboratory 
use (TZS 59) shall be used  in tests.  
 
A-2. Preparation of sample  
Procedure  - Crush 50 g of sample to pass through a 1.00 mm sieve. Dry to constant mass at               
105 ± 5°C to obtain the prepared sample  and keep in a clean, glass -stoppered bottle in a desiccator 
for test purposes.  
 
A-3. Determination of sodium sul fate (as Na 2SO 4) 
A-3.1 Principle - Sodium sulfate is determined by precipitation with barium chloride solution and 
weigh ed as barium  sulfate. 
 
A-3.2 Reagents  
A-3.2.1 Barium Chloride Solution - approximately 10 percent.  
A-3.2.2 Dilute Hydrochloric Acid - approximately 4 N.  
 
A-3.3 Procedure  
A-3.3.1 Weigh about 0.2 g of the prepared sample and dissolve 100 m L of water. Filter to remove 
undissolved matter s and wash the filter paper thoroughly. To the filtrate and washings , add 10 m L of 
dilute hydrochloric acid and boil. Add slowly to the hot solution a slight excess of hot barium chloride 
solution and continue boiling for 2 min to obtain a granular precipitate of barium sul fate. Allow to  
stand for 4 hours and filter through a tared sintered glass crucible (G No.4). Wash the precipitate 
thoroughly and dry at 105  to 110°C  to constant mass . 
 
A-3.3.2 An excess of barium chloride is necessary to reduce the solubility of barium sulphate. 
Precipitation in hot solution by the addition of barium chloride slow ly with constant stirring minimizes 
mechanical  occlusion of barium chloride and gives a coarse precipitate which is less  soluble in acids.  
 
A-3.3.4 Calculation  
Sodium sulphate (as Na 2SO4), percent by mas s =  100  𝑀
𝑀1 
 
where  
M = mass in g of the dried precipitate, and  
M1 = mass in g of the material taken for the test.  
 
A-4. Determination of matter insoluble in water  
 
A-4.1 Procedure   
Weigh about 10 g of the prepared sample. Dissolve in 100 m L of water by warming, if necessary, and by 
stirring the  solution . Filter through a tared filter paper or sintered crucible ( G No.4). Wash thoroughly the 
residue till it is free  from all soluble compounds and dry at 105 to 110 °C  to constant mass.  
 
A-4.2 Calculation  
Matter insoluble in water, percent by mass =  100  𝑀
𝑀1 
   
4 
 Where,  
M = mass in g of the residue, and  
M1 = mass in g of the prepared sample taken for the test  
 
A-5. Determination of chlorides (as NaCl)  
A-5.1 Principle  - Chlorides are determined by precipitating with silver  nitrate solution and titrating the 
excess of silver nitrate solution with,  standard ammonium  thiocyanate solution using ferric alum as 
indicator  
 
A-5.2 Reagents  
A-5.2.1 Standard silver nitrate – 0.1 N 
A-5.2.2 Concentrated nitric acid  
A-5.2.3 Ferric alum indicator  solution - saturated,  
A-5.2.4 Standard ammonium  thiocyanate solution – 0.1 N 
A-5.2.5 Nitrobenzene  
 
A-5.3 Procedure  
Weigh about 5 g of the prepared sample  and dissolve in  80 m L of water. Filter the residue, if any, 
through a  folded filter paper and wash thoroughly with water, collect the filtrate  and washings in a 250  
mL conical flask. Add with a pipette 25 m L of standard  silver nitrate solution, 2 m L of concentrated 
nitric acid and 10 m L, of nitrobenzene.  Shake vigorously and add 2 m L of ferric alum indicator 
solution.  Titrate the solution with standard ammonium thiocyanate solution to the  first persistent 
colour change.  
 
A-5.4 Calculation  
Chlorides (as NaC l), percent by mass = 0.5846  (25−𝑉)
𝑀 
 
where  
V = volume in m L of standard ammonium thiocyanate solution used in the titration, and  
M = mass in g of the prepared sample taken for the test.  
 
A-6. Determination of Iron, Aluminium and Chromium (as R2O3) 
A-6.1 Principle - Iron, aluminium and chromium compounds are  determined  by precipitation with 
ammonium  hydroxide.  
 
A-6.2 Reagents  
A-6.2.1  Ammonium chloride – Solid  
A-6.2.2  Dilute Ammonium Hydroxide - approximately 4 N.  
A-6.2.3  Ammonium Nitrate Solution - approximately 2 percent.  
A-6.2.4  Dilute Hydrochloric Acid - approximately 4 N.  
A-6.2.5 Conc. N itric acid  
 
A-6.3 Procedure  
Weigh about 10 g of the prepared sample and dissolve in 150 mL of water. Acidify with dilute 
hydrochloric acid,  add 2 to 3 drops of concentrated nitric acid, boil for 1 to 2 min, and then filter to 
remove undissolved matter. Wash the filter paper thoroughly and, to the hot solution add, first 3 to 5  g 
of ammonium chloride and then ammonium hydroxide solution till there is a faint permanent smell of 
ammonia (in order to precipitate completely the iron, aluminium and chromium as hydroxides ). Boil  
the contents  for 2 min and filter through Whatman filter  paper No. 40 or equivalent. Wash with hot 
ammonium nitrate solution till free from chlorides. Dry the precipitate at 100 ±  2°C and ignite at 1 100 
°C in a tared crucible to constant mass.  
 
A-6.3 Calc ulation  
Iron, Aluminium and Chromium  (R2O3), percent by mass  = 100  𝑀1
𝑀2 
  
©TBS 2020 – All rights reserved                                                                                              5 where  
M1 = mass in g of the ignited residue, and  
M2 = mass in g of the prepared sample taken for the test.  
 
A-7. Determination of iron  (as Fe ) by Colorimetric Method  
 
A-7.1 Principle - Iron is determined colorimetrically by visual comparison of the colour in Nessler 
cylinders, using -potassium thiocyanate.  
 
A-7.2 Apparatus  
Nessler cylinders - 50 mL capacity.  
 
A-7.3 Reagents  
A-7.3.1 Concentrated nitric acid  
A-7.3.2 Ammonium persul fate - solid. 
A-7.3.3 Butanolic potassium thiocyanate - Dissolve 10 g of potassium thiocyanate in 10 m L of water. 
Add suffici ent n-butanol to make up to 100 m L and shake vigorously until the solution is clear . 
 
A-7.3.4 Dilute sul furic acid  - approximately 10 percent (v/v).  
Weigh 0.702 g of ferrous ammonium sul fate [ FeSO 4 (NH 4) SO 4.6H 2O] and dissolve in 10 m L of dilute 
sulfuric acid.  Dilute with water to make up the volume to 1000 m L. Transfer 10 mL  of this  solution and 
again dilute with water to make up the volume to 100 mL . 1 mL  of this solution is equivalent to 0.01 
mg of iron (as Fe).  
 
A-7.4 Procedure  
Weigh about 1 g of the prepared  sample, dissolve it in water and make up the volume to 100 m L. 
Pipette out  exactly 10 m L of this solution into a beaker, add 1 mL  of nitric acid and  boil. Cool, transfer 
the solution to a Nessler cylinder and add 30 mg of  ammonium persul fate and 15 m L of butanolic  
potassium thiocyanate  solution. Shake the contents vigorously for 30 s and then allow the liquid to 
separate.  Carry out a control test in the other Nessler cylinder adding slowly from a  burette  a quantity 
of the standard iron solution in plac e of the material  and the same quantities of other reagents in the 
same total volume of the  reaction mixture until the colours of butanol layer in the two cylinders  are 
exactly matched . 
 
A-7.5 Calculation  
Iron (as Fe), percent by mass = 0.01𝑉
𝑀 
 
Where  
V = volume in m L of standard iron solution required in the  control test, and  
M = mass in g of the material taken for the test.  
 
A-8. Determination of loss on drying  
 
A-8.1 Procedure - Weigh about 5 g of the crushed material into a tared dish and dry at      105 ± 5°C. 
Cool and weigh  repeatedly till a constant mass is , obtained.  
 
A-8.2 Calculation  
 
Loss on drying, percent by mass = 100  𝑀1− 𝑀2
𝑀1 
 
where  
M1= mass in g of the material taken for the test, and  
M2 = mass in g of the residue obtained after drying.  
 
A-9. Determination of pH  
Procedure - Weigh 5 g of the prepared sample and dissolve in 50 m L of water. Determine the pH of 
the solution with the suitable calibrated pH meter, using glass and calomel  electrode.   
6 
  
Annex B  
(normative)  
 
Sampling of sodium sulphate, anhydrous  
 
 
B-1. General requirements of sampling  
B-1.0 In drawing, preparing, storing and handling test samples the following  precautions and 
directions shall be observed.  
B-1.1 Precautions shall be taken to protect the samples, the material being  sampled, the sampling 
instrument and the containers for samples from  adventitious contamination.  
B-1.2 To draw a representative sample, the contents of each container  selected for sampl ing shall be 
mixed as  thoroughly as possible by suitable  means.  
B-1.3 The samples shall be placed in suitable, clean, dry and air -tight glass or other suitable 
containers on which the material has no action.  
B-1.4 Each sample container shall be sealed air -tight after filling  and marked with full details of 
sampling, the date of sampling and the year  of manufacture of the material.  
 
B-2. Scale of sampling  
B-2.1 Lot - All the containers in a single consignment of the materia l of one grade and drawn from a 
single batch of manufacture shall constitute  a lot. If a consignment is declared or known to consist of 
different grades  or batches of manufacture, the containers belonging to the same grade  and batch 
shall be grouped together and each such group shall constitute a separate lot. 
B-2.2 Samples shall be tested from each lot for ascertaining the conformity  of the material to the 
requirements of the specifica tion. 
B-2.3 The number (n) of containers to be chosen from a lot shall depend  on the size of the lot ( N) and 
shall be in accordance with col 1 and 2 of  Table 2.  
 
Table 2 number of containers to be selected  
 
Lot Size  Number of Containers to be selected  
N n 
3 to 50  3 
51 to 200  4 
201 to 400  5 
401 to 650  6 
651 and above  7 
 
B-2.4 The containers to be selected for sampling shall be chosen at random  from the lot and for this 
purpose random number tables shall be used.  In case such tables are not available, the following 
procedure may be  adopted:  Starting from any container, count them as 1, 2, 3 .... up to r and so  on in 
a systematic manner, where r is the integral part of N/n. Every rth container thus counted shall be 
taken out for drawing samples . 
 
B-3. Test samples and referee sample  
 
B-3.1 Preparation of Test Samples  
B-3.1.1  Draw with an appropriate sampling instrument a sm all portion  of the material from different 
parts of each container selected. The total  quantity of the material drawn from each container shall be 
sufficient  to conduct the tests for all the characteristics given in  4 and shall not  exceed 1 kg. 
 
B-3.1.2  Thoroughly mix all portions of the material drawn from the  same container. Out of these 
portions a small but equal quantity shall be  taken from each selected container and shall be well 
mixed up together  so as to form a composite sample weighing not less than 600 g. This composite  
sample shall be divided into three  equal parts, one for the purchaser,  another for the supplier and the 
third to be used as refere nce sample.  
  
©TBS 2020 – All rights reserved                                                                                              7 B-3.1.3  The remaining portion of the material from each container  (after a small quantity needed for 
the formation of composite sample  has been taken) shall be divided into three equal parts, each 
weighing  not less than 100 g. These parts shall be immediately tra nsferred to thoroughly  dried bottles 
which are then sealed air -tight with stoppers and  labelled with all the particulars of sampling given in 
B-1.4. The material  in each such  sealed bottle shall constitute an individual test sample. These  
individual sample s shall be separated into three identical sets of samples  in such a way that each set 
has an individual test sample representing each  container selected. One of these three sets shall be 
sent to the purchaser,  another to the supplier and the third shall be  used as refere nce sample.  
 
B-3.2 Refere nce Sample  
The refere nce sample shall consist of the composite  sample ( see B-3.1.2) and a set of individual 
samples (see B-3.1.3) marked  for this purpose and shall bear the seals of the purchaser and the 
supplier.  These shall be kept at a place' agreed to between the purchaser and the  supplier and shall 
be used in case of dispute between the two.  
 
B-4. Number of tests  
Tests for the determination of sodium sulphate shall be conducted  on each of the individu al samples 
for all the grades.  
 
B-4.2 Tests for the remaining characteristics shall be conducted on the  composite sample.  
 
B-5. Criteria for Conformity  
 
B-5.1 For individual samples  
For sodium sulfate - The test results for sodium sul fate shall be  recorded ; the mean and the range for 
these test results calculated as  follows:  
 
Mean (x) = Sum of the test results divided by the number of test  results, and  Range (R) = Difference 
between the maximum and minimum values  of test results.  The value of expression X - 0.6 R shall be 
calculated. If the value of  this expression is more than or equal to the limit specified for the relevant  
grade in Table 1, the lot shall be declared to have satisfied the requirements  for this characteristic.  
 
B-5.2 For composite sample  
The test results on the composite sample shall meet the corresponding requirements.  
 
B-5.3 A lot shall be declared as conforming to the specification if it satisfies the requirements for each 
of the characteristics.