ICS 71.100.70  
 
Reference number  
DRS 89: 202 1 
© RSB 2021 
  
 RWANDA 
STANDARD  DRS 
89 
 
Second edition  
2021-mm-dd 
 
Baby toilet soaps  — Specification   
   
DRS 89: 202 1 
©RSB 2021 - All rights reserved              ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2021 
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reprodu ce this document should be addressed to : 
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E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw   DRS 89: 202 1 
iii                ©RSB 2021 - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ...................  iv 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Normative references  ................................ ................................ ................................ ...................  1 
3 Terms and definitions  ................................ ................................ ................................ ..................  1 
4 Requirements  ................................ ................................ ................................ ................................  1 
4.1 General requirements  ................................ ................................ ................................ ..................  1 
4.2 Specific requirements  ................................ ................................ ................................ ..................  2 
5 Packag ing and labelling ................................ ................................ ................................ ...............  3 
5.1 Packaging  ................................ ................................ ................................ ................................ ...... 3 
5.2 Labelling  ................................ ................................ ................................ ................................ ........  3 
6 Sampling  ................................ ................................ ................................ ................................ ....... 4 
Annex  A (normative)  Test for freedom from grit  ................................ ................................ ...................  5 
A.1 Outline of the method  ................................ ................................ ................................ ..................  5 
A.2 Procedure  ................................ ................................ ................................ ................................ ...... 5 
Annex  B (normative)  Determination of Nickel  ................................ ................................ .......................  6 
B.1 Outline of the method  ................................ ................................ ................................ ..................  6 
B.2 Reagents  ................................ ................................ ................................ ................................ ....... 6 
B.3 Procedure  ................................ ................................ ................................ ................................ ...... 6 
Annex  C (normative)  Determination of iron  ................................ ................................ ...........................  8 
C.1 Outline of the method  ................................ ................................ ................................ ..................  8 
C.2 Apparatus  ................................ ................................ ................................ ................................ ...... 8 
C.3 Reagents  ................................ ................................ ................................ ................................ ....... 8 
C.4 Procedure  ................................ ................................ ................................ ................................ ...... 8 
Annex  D (normative)  Determination of copper  ................................ ................................ ...................  10 
D.1 Outline of the method  ................................ ................................ ................................ ................  10 
D.2 Apparatus  ................................ ................................ ................................ ................................ .... 10 
D.3 Reagents  ................................ ................................ ................................ ................................ ..... 10 
D.4 Procedure  ................................ ................................ ................................ ................................ .... 10 
Annex  E (normative)  Identification of rosin content of fatty mater in soaps  ................................ ... 11 
E.1 Scope  ................................ ................................ ................................ ................................ ...........  11 
E.2 Reagents  ................................ ................................ ................................ ................................ ..... 11 
E.3 Procedure  ................................ ................................ ................................ ................................ .... 11 
Annex  F (normative)  Determination of rosin content of fatty mater in soaps  ................................ . 13 
F.1 Scope  ................................ ................................ ................................ ................................ ...........  13 
F.2 Reagents  ................................ ................................ ................................ ................................ ..... 13 
F.3 Procedure  ................................ ................................ ................................ ................................ .... 15 
F.4 Calculation  ................................ ................................ ................................ ................................ .. 16 
 DRS 89: 202 1 
©RSB 2021 - All rights reserved              iv 
 Foreword   
Rwanda Standard s are prepared  by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards adop ted 
by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
DRS 89 was prepared by Technical Committee RSB/TC 42, Surface Active Agents . 
In the preparation of this standard, reference was made to the following standard:  
WD-ARS 1460 : Baby toilet soaps — Specification  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This second edition cancels and replaces the first edition (RS  89: 2015 ), of which has been technically revised.  
 
Committee membership  
The following organizations were represented on the Technical Committee on Surface Active Agents  (RSB/TC 
42) in the preparation of this standard.  
Paragraph of p articipants  
 
Rwanda  Standards Board  (RSB) – Secretariat  DRS 89: 202 1 
v                ©RSB 2021 - All rights reserved  
 Introduction   
A paragraph.  Normally the general requirements for a baby toilet soap are  similar to those prescribed for toilet 
soap meant for adults. However,  on account of natural difference between a baby's skin and an adult's  skin due 
regard to toxicity and dermatological consideration is given during the manufacture of baby  toilet soap. This is 
because the skin of  babies, being much thinner and less cornified than that of an adult, is  highly susceptible to 
irritation and resistance to bact erial attack is not fully developed in the very young ones. If superficial layers of 
the epidermis are damaged by any means, for example, by the use of harsh  toiletries, various skin disorders 
may develop. It is however not  practicable to prescribe all suc h factors. It is, therefore, emphasized  that 
manufacturers of baby toilet soap shall take the responsibility to  establish and ensure de rmatological safety of 
the soap.  
In order to achieve dermatological safety of baby toilet soap the  choice and selection of appropriate quality and 
quantity of different  raw materials is very important.  
In this specification, unlike normal toilet soap, the use of rosin has  not been allowed because on account of its 
unsaturated nature, its soap  may lead to irritation of the s kin. On similar consideration a higher  limit for total 
fatty matter  (78%), low limits for free caustic alkali and free  carbonated alkali and low limits for heavy metals, 
namely, nickel, copper and iron have been prescribed.  
 
 DRS 89: 202 1 
1                ©RSB 2021 - All rights reserved  
 Baby toilet soap  — Specification  
1 Scope   
This Draft Rwanda Standard  specifies requirements, sampling and test methods for baby toilet soap . 
2 Normative references   
The following documents are 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 t he referenced document (including any amendments) applies.  
DARS 489 -2017, Toilet soap — Specification  
ISO 456, Surface active agents — Analysis of soaps — Determination of free caustic alkali  
 
ISO 457, Soaps — Determination of chloride content — Titrimetric method  
 
ISO 672 , Soaps — Determination of moisture and volatile matter content — Oven method  
 
ISO 673, Soaps — Determination of content of ethanol -insoluble matter  
 
ISO 684, Analysis of soaps — Determination of total free alkali  
 
ISO 685, Analy sis of soaps — Determination of total alkali content and total fatty matter content  
ISO 862, Surface active agents — Vocabulary  
ISO 8212, Soaps and detergents — Techniques of sampling during manufacture  
 
ISO 6839 , Anionic surface active agents — Determinat ion of solubility in water  
3 Terms and definitions   
For the purposes of this standard, the terms and definitions given in RS ISO 862  apply.  
4 Requirements  
4.1 General requirements  
4.1.1  Baby toilet soaps shall contain only the following:  Colouring matter, perfume,  preservatives and super 
fatting agents.  All other in gredients  exce pt moisture shall he declared on the label.  All these materials shall be 
non-injurious to skin in use with soap.  (In accordance with RS EAS 377, all parts )  
©RSB 2021 - All rights reserved              2 
 4.1.2  Baby toilet soap shall be a  high grade, thoroughly saponified, milled soap or homogenized soap or 
both, white or coloured, mildly perfumed or unperfumed, and compressed in firm smooth cakes. It shall possess 
good cleaning and lathering properties. It shall  be free from rancidity.  
4.1.3  Baby soap shall have no objectionable odour, shall have good fathering and cleansing properties  and 
shall be free from grit when tested in accordance to Annex A.  
4.1.4  Baby soap may contain chelating agents, colouring matter, medicaments, mild perfum e and  
antioxidants which shall be non -injurious in use with soap . 
4.1.5  Baby soap shall not contain any r esins. 
4.2 Specific requirements  
Baby toilet soap shall comply with the  specific requirements given in  Table 1, when tested according to the 
corresponding test methods.   
Table 1 — Specific  requirements for baby toilet soap  
S. No.  Characteristic  Requirements  Method of test  
i)  Total fatty matter, percent by mass, Min  78.0 ISO 685  
ii)  Moisture and volatile matter (at 105  °C), percent 
by mass , Max  15.0 ISO 672 
iii)  Matter insoluble in alcohol , percent by mass, 
Max  2.0 ISO 673  
iv)  Matter insoluble in water, percent by mass , Max  0.5 ISO 6839  
v)  Free caustic alkali, as sodium hydroxide 
(NaOH), percent by mass, Ma x 0.03 ISO 456  
vi)  Chlorides, as  sodium chloride (NaCI), percent 
by mass, Ma x 1.0 ISO 457  
vii)  Free carbonated alkali, percent by mass, Max  0.5 ISO 684  
viii)  Freedom f rom grit  To pass the test  Annex A 
ix)  Nickel content  Nil Annex B 
x)  Iron content, parts per million, Ma x 10 Annex C 
xi)  Copper (as Cu) contents, parts  3 Annex D 
xii)  Freedom f rom resin  To pass the test  Annexes E and F  
Baby toilet soap is liable to lose moisture on keeping. The results of analysis in respect of other characteristics 
shall be recalculated in relation to the minimum specified total fatty matter by means of the equations:  
matterfatty  total Actualmatterfatty  total specified Minimum result  Actual result ed Recalculat  
 DRS 89: 202 1 
3                ©RSB 2021 - All rights reserved  
 Where the minimum specified total fatty matter = 78.0%  
The weight of the baby toilet soap is also liable to diminish owing the loss of moisture in the  soap. The weight 
of the baby toilet soap cakes or tablets shall be recalculated by means of the equation:  
 X = Recalculated weight of soap before drying = actual weight x 𝐴𝑐𝑡𝑢𝑎𝑙  𝑇𝐹𝑀
𝑚𝑖𝑛𝑖𝑚𝑢𝑚  𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑒𝑑  𝑇𝐹𝑀 
5 Packaging and labelling  
5.1 Packaging  
Each cake or a number of cakes of Baby toilet soap shall be wrapped in a suitable protective wrapper. The 
wrapped cakes shall then be packed in suitable containers to form a tight package which protects the cakes 
from contamination.  
5.2 Labelling  
5.2.1  The packages shall be securely closed and labelled in  conformity with the statutory requirements as 
applicable from time to time and the following:  
a) Name of the material;  
b) Manufacturer's name and address and/or his recognized trade -mark, if any;  
c) Net ma ss when packed;  
d) Total fatty matter content;  
e) Batch No. or Lot No. in code or otherwise; and Month and year of manufacture.  
f) The following identified critical ingredients in descending order of quantity, percent by mass:  
1) Total fatty matter (TFM), and  
2) Water in soluble matter.  
g) The words ‘baby soap’  
h) Country of origin  
i) list of ingredients; and 
j) manufacture and expiry dates   
©RSB 2021 - All rights reserved              4 
 5.2.2 The packages may also be marked with a Certification  Mark.  
6 Sampling  
For this purpose, scale of sampling and preparation of test samples  shall be as prescribed in ISO 8212 . DRS 89: 202 1 
5                ©RSB 2021 - All rights reserved  
 Annex  A 
(normative)  
 
Test for freedom from grit  
A.1 Outline of the method  
Soap is rubbed with water between the hands for a specified  time and examined for its gritty or rough feel, if 
any. 
A.2 Procedure  
A.2.1  Hold a bar of soap in run ning tap water and rub between both  hands for about 3 minutes. No gritty or 
rough feel should be perceived  while rubbing the soap surface. Examine the surface of the bar which  shall not 
be rough and shall feel smooth when the fingers are moved  across the s urface. Set the bar on and let it dry for 
24 hours at room  temperature and examine its surface.  
A.2.2  The soap shall he taken to have passed the test if there is no  gritty or rough feel on the surface.  
 
   
©RSB 2021 - All rights reserved              6 
 Annex  B 
(normative)  
 
Determination of Nickel  
B.1 Outline of the method  
The method is based on the isolation of metal from the soap and  reaction between nickel in the oxidized form 
with dimethyl glyoxime  forming a red colour.  
B.2 Reagents  
B.2.1  Sodium hydroxide  — AR grade.  
B.2.2 Concentrated hydrochloric acid — Conformi ng to  relevant standard . 
B.2.3 Dimethyl glyoxime solution — 0.1 percent ( v/v) in 95 percent ethyl alcohol.  
B.2.4 Saturated bromine water 
B.2.5 Liquor ammonia — Relative density 0.9.  
B.3 Procedure  
B.3.1  Isolation of metal from soap  
B.3.1.1  Weigh 50 g of soap in  a beaker and dissolve in hot water. Add to this soap solution 40 ml of  
concentrated hydrochloric acid, stir and keep on steam bath until fatty  acid layer separates. Add 20 g of paraffin 
wax, stir at intervals and  allow it to settle until phases are clear.  Cool to room temperature.  
B.3.1.2 Remove wax cake with rod, rinse with water and add rinsings  to aqueous phase. Evaporate, aqueous 
phase to about 60 ml by gentle  boiling. Add 100 ml of water and filter through paper washed  previously with 
hydrochloric aci d. Evaporate filtrate and washings to  about 60 ml. Cool and transfer to volumetric flask. Make 
up the  volume to 100 ml. Take aliquot portions for metal estimation.  
B.3.2  Determination of Nickel content  
B.3.2.1  Take 50 ml aliquot of the  aqueous solution fro m the test solution in a 250 -ml beaker.  
B.3.2.2  Evaporate  the solution to about 15 ml by heating.  
B.3.2.3  Transfer the solution to a 50 -ml glass stoppered volumetric flask using a small quantity of water for  
rinsing the solution from the beaker into the volumetric flask.  DRS 89: 202 1 
7                ©RSB 2021 - All rights reserved  
 B.3.2.4  Add to the  flask 3 ml of saturated bromine water and allow to stand for one minute.   
B.3.2.5  Add liquor ammonia dropwise until excess bromine is destroyed as  indicated by the disappearance of 
brown colour.  
B.3.2.6  Then add 5 ml of liquor  ammonia in excess. If a precipitation occurs, filter the solution and wash  the 
precipitate with distilled water; combine the filtrate and the  washings and concentrate to a volume of a few 
millilitres and transfer  to a 50 -ml volumetric flask.  
B.3.2.7 Add 10 ml of dimetyl glyoxime solution,  followed by 15 -20 ml of 95 percent ethyl alcohol. Mix thoroughly 
and make up the volume and again mix thoroughly.  
B.3.2.8  Allow the solution to  stand for 5 minutes to permit full development of colour. The samp le shall be 
considered to have passed the test if no pink colour develops.   
©RSB 2021 - All rights reserved              8 
 Annex  C 
(normative)  
 
Determination of iron  
C.1 Outline of the method  
The method is based on the isolation of metal from the soap by  dissolving in hot water. The aqueous extract is 
treated with  citric acid  to sequester aluminium and then thioglycolic acid in ammoniacal  solution is added and 
colour measured spectrophotometrically.  
C.2 Apparatus  
Spectrophotometer  
C.3 Reagents  
C.3.1  Liquor ammonia  — Relative density 0.9.  
C.3.2 Sulfuric acid — 50 percent (v/v). 
C.3.3 Citric acid (aqueous solution)  — 50 percent ( v/v). 
C.3.4 Thioglycolic acid (aqueous solution)  
C.3.5 Standard iron solution  — Containing 10 µg of iron per ml prepared from ferric ammonium sulphate 
[Fe 2(SO 4)3.(NH 4)2SO 4.12H 2O] in acid solution.  
C.3.6 Methyl red indicator  — 0.1 percent aqueous solution.  
C.4 Procedure  
C.4.1  Isolation of metals from soap 
Weigh 50 g of the soap  sample in a beaker and dissolve it with hot water. To this soap solution  add 40 ml of 
concentrated hydrochloric acid with constant  stirring and  keep the beaker on steam bath until fatty acid layer 
separates. Add  20 g of paraffin wax to this solution while hot. Stir the solution at  intervals and allow it to settle 
until phases are clear. Cool the mass to  room temperature. Remove the w ax cake with rod, rinse with water  and 
add the rinsings to aqueous phase. Evaporate the aqueous phase  to above 60 ml by gentle boiling. Add 100 ml 
of water and filter  through paper washed previously with hydrochloric acid. Evaporate  the filtrate and washin gs 
to about 60 ml. Cool and transfer the  solution to a volumetric flask and make up the volume to 100 ml. Take  
aliquot portion of the solution for metal estimation.  
C.4.2  Determination of iron DRS 89: 202 1 
9                ©RSB 2021 - All rights reserved  
 Take 5 ml aliquot of the aqueous  solution from the test solutio n in a 25 -ml volumetric flask. To this add  4 ml 
citric acid solution and 0.02 ml methyl red indicator and liquor  ammonia till the colour of the solution turns yellow. 
Then add 3 ml  liquor ammonia in excess. Cool the solution and add 3 ml thioglycolic  acid.  Make up the volume 
to 25 ml and mix the solution thoroughly.  Filter the solution through acid washed and dried filter paper. Measure  
absorbance of the clear solution at 540 nm in the spectrophotometer  using water as reference. Prepare a 
calibration curve with standard  iron solution and determine the iron content of the soap sample from it.   
©RSB 2021 - All rights reserved              10 
 Annex  D 
(normative)  
 
Determination of copper  
D.1 Outline of the method  
The method is based on the isolation of metal from the soap and  to make a copper complex using zinc dibenzyl 
dithiocarbamate in  carbon tetrachloride solution and measure the colour of the solution  spectrophotometrically.  
D.2 Apparatus  
Spectrophotometer  
D.3 Reagents  
D.3.1  Zinc dibenzyl  dithiocarbamate solution  — 0.05 percent in  (v/v) in carbon tetrachloride.  
D.3.2 Standard copper solution  — Containing 1 pg of copper per  ml (prepared from a stock solution of 100 
times the concentration).  
D.4 Procedure  
D.4.1  Isolation of metal from soap 
Weigh 50 g of soap sample in  a beaker and dissolve it with hot water. To this soap solution add  40 ml of 
concentrated hydrochloric acid with constant stirring and  keep the beaker on steam bath until fatty acid layer 
separates. Add  20 g of paraffin wax to this solution while hot. Stir the solution at  intervals and allow it to settle 
until phases are clear. Cool the mass to  room temperature. Remove the wax cake with rod, rinse with water  and 
add the rinsings to aqueous phase. Evaporate the aqueous phase  to about 60 ml by gentle boiling. Add 100 ml 
of water and filter  through filter paper wa shed previously with hydrochloric acid.  Evaporate the filtrate and 
washings to about 60 ml. Cool and transfer  the solution to a volumetric flask and made up the volume to 100 
ml. Take aliquot portion of the solution for metal estimation.  
D.4.2  Determinatio n of copper  
Take 20 ml aliquot of the aqueous solution and to it add 10 ml of zinc debenzyl dithiocarbamate solution followed 
by 25 ml sulphuric acid in a separating funnel. Shake the solution for one minute and allow it to settle. Run the 
lower carbon tet rachloride layer in to a 25 ml volumetric flask. Wash the aqueous layer with carbon tetrachloride 
and transfer through glasswool to volumetric flask. Make up the volume and mix well. Measure absorption of 
the clear solution at 435 nm in the spectrophotomet er. Prepare a calibration curve with standard copper solution 
and determine the copper content of the soap sample from the curve.  
NOTE  The standard solution shall also be extracted with carbon tetrachloride before estimation of colour.  DRS 89: 202 1 
11                ©RSB 2021 - All rights reserved  
 Annex  E 
(normative)  
 
Identi fication of  rosin content of fatty mater in soaps  
E.1 Scope  
This Annex  specifies the Halphen -Grimaldi and Liebermann -Storch method for the identification of rosin in fatty 
matter.  
E.2 Reagents  
NOTE  Use only analytical grade reagents and distilled water.  
E.2.1 Acetic anhydride.  
E.2.2 Sulphuric acid, density 1 .53 g/mL. Cautiously add 97 mL of sulphuric acid (density  1.84 g/mL) to 
100 mL of water.  
E.2.3 Solution A. Dissolve 10 g of phenol in 27 mL of chloroform.  
E.2.4 Solution B. Dissolve 10 mL of bromine in 40 mL  of chloroform.  
E.3 Procedure  
E.3.1 Halphen -Grimaldi method  
E.3.1.1 Place one or two drops of the fatty matter, reserved from the determination of fatty matter  (ISO 685 ), 
in a porcelain basin and add approximately 2 mL of the solution A to dissolve it. Wet  the walls of the basin by 
tilting and turning it and let it stand for a few seconds so that the walls of  the basin are covered with a very thin 
film of the solution.  
E.3.1.2 Hold the neck of the flask containing the solution B in such a position that the bromine  vapour diffuses 
into the porcelain dish and comes into contact with the walls. In the presence of  rosin a blueish -grey to purple 
colour develops immediately.  
E.3.1.3 Carry out a comparison test with a sample of fatty matter to which 2 % ( m/m) of ro sin has  been added.  
NOTE  Should the colour reaction in A.3.1.2 be masked by other colours, conduct a second qualitative test, using the Liebermann -
Storch method.  
E.3.2 Liebermann -Storch method   
©RSB 2021 - All rights reserved              12 
 E.3.2.1 Place 1 g - 2 g of the fatty matter in a test tube, add  5 mL - 10 mL of the acetic anhydride,  and heat 
the mixture in a boiling water bath for approximately 3 min. Cool to room temperature and  pour 1 mL - 2 mL of 
the solution into a white porcelain basin.  
E.3.2.2 Allow one or two drops of the sulphuric acid to  run down the side of the basin. If rosin is  present, a 
violet colour immediately develops where the acid is in contact with the solution. This  colour then turns brown 
on standing.  
E.3.2.3 Carry out a comparison test with a sample of fatty matter to which 2 % ( m/m) of rosin has  been added.  DRS 89: 202 1 
13                ©RSB 2021 - All rights reserved  
 Annex  F 
(normative)  
 
Determination of rosin content of fatty mater in soaps  
F.1 Scope  
This Annex  specifies a method for the determination of the rosin content of fatty matter in soaps.  
NOTE 1  Before proceeding with the quantitative determination of rosin, first establish its presence by a qualitative test (see Annex  E). 
NOTE 2  The following method is not accurate for rosin concentrations below a mass fraction of 5 %.  
F.2 Reagents  
NOTE  Use only anal ytical grade reagents and distilled water.  
F.2.1 Diethyl ether  
Free from peroxides.  
F.2.2 Sodium chloride  
F.2.3 Sodium sulfate  
Anhydrous.  
F.2.4 Hydrochloric acid solution  
Dilute one volume of concentrated hydrochloric acid (density 1 .16 g/mL) with two volu mes of  distilled water.  
F.2.5 Sodium hydroxide solution  
10 % mass fraction aqueous solution.  
F.2.6 Naphthalene -2-sulfonic acid solution  
Dissolve 40 g of naphthalene -2-sulfonic acid in 1 L of absolute methanol.  
F.2.7 Sodium chloride solution, saturated   
©RSB 2021 - All rights reserved              14 
 Shak e an excess of sodium chloride with water at ambient temperature until no more dissolves.  Keep the 
solution over solid sodium chloride.  
F.2.8 Sodium chloride solution, 10 %  
Dissolve 10 g of sodium chloride in 100 mL of water.  
F.2.9 Standard ethanolic potassium hydroxide solution, 0 .2 N 
F.2.9.1 Preparation  
Purify 95 % (by volume fraction) ethanol by boiling 1 .5 L of it over 20 g of potassium hydroxide for  1 h under 
reflux. Distil, discarding the first 50 mL of the distillate and stopping the distillation when  approximately 1 .3 L 
have been distilled. Dissolve 12 g of potassium hydroxide in 1 L of the purified  ethanol, allow the solution to 
stand for approximately one week, and then decant the clear  supernatant liquid from any potassium carbonat e 
that has precipitated.  
F.2.9.2 Standardization  
Accurately weigh out approximately 1 g of potassium hydrogen phthalate (previously dried at  110 °C ± 5 °C for 
3 h) into a 250 mL Erlenmeyer flask. Add approximately 100 mL of carbon  dioxide -free distilled wa ter and three 
drops to five drops of the phenolphthalein indicator, and swirl  gently until the solid has dissolved. Titrate the 
solution with the standard ethanolic potassium  hydroxide solution, until a permanent pink colour is formed.  
F.2.9.3 Calculation  
Normality of the standard ethanolic potassium hydroxide solution ( N): 
B. AN8974
 
where  
A is the mass of the potassium hydrogen phthalate, in grams;  
B is the volume of the standard ethanolic potassium hydroxide solution used for the  titration, in 
millilitres.  
F.2.10 Methyl orange indicator  
Dissolve 0 .2 g of methyl orange in 100 mL of carbon dioxide -free water.  
F.2.11 Phenolphthalein indicator  
Dissolve 0 .5 g of phenolphthalein in 100 mL of freshly boiled, 95 % (by volume fraction) ethanol.  DRS 89: 202 1 
15                ©RSB 2021 - All rights reserved  
 F.3 Proced ure 
F.3.1  Preparation of fatty matter  
F.3.1.1  Carbolic  soaps  
F.3.1.1.1  Weigh out accurately into a 600 mL beaker such quantity of the test sample as contains  approximately 
40 g of fatty matter and dissolve it in approximately 400 mL of hot water, to which  40 mL of the sodium hydroxide 
solution has been added.  
F.3.1.1.2  Salt out the soap by adding sufficient sodium chloride to the hot solution to saturate it (at  ambient 
temperature) with sodium chloride. Filter the soap quantitatively, and allow it to drain.  
F.3.1.1.3  Dissolve the drained soap in approximately 400 mL of hot water, and repeat the salting out  and filtering 
procedure.  
F.3.1.1.4  Wash the soap thoroughly with the saturated sodium chloride solution, and proceed in  accordance 
with F.3.1.2.2 to F.3.1.2.7.  
F.3.1.1.5 Reserve the combined filtrates and washings for the determination of carbolic acids.  
F.3.1.2 Other soaps  
F.3.1.2.1  Weigh accurately into a 600 mL beaker such quantity of the test sample as contains  approximately 40 
g of fatty matter.  
F.3.1.2.2  Dissolve the soap in approximately 400 mL of hot distilled water, cool the solution, and  slowly add an 
excess of the hydrochloric acid solution. Cover the beaker with a watch -glass and  heat the contents until the 
fatty matter separates into a clear l ayer, but do not allow the temperature  to exceed 60 °C.  
F.3.1.2.3  In the cases of liquid and gel soaps, acidify the soap as it is.  
F.3.1.2.4  Cool to approximately 25 °C and transfer the contents of the beaker to a separating funnel.  Rinse the 
watch -glass a nd the beaker with portions of the diethyl ether totalling 100 mL and add  them to the separating 
funnel. Shake the mixture in the separating funnel vigorously for 1 min, and  let it stand until the two phases have 
separated.  
F.3.1.2.5  Draw off and discard t he aqueous layer and wash the ether extract with 50 mL portions of  the sodium 
chloride solution until the last washing is neutral to the methyl orange indicator.  
F.3.1.2.6  Filter the washed ether extract into a 250 mL beaker through a filter paper containi ng approximately 5 
g of anhydrous sodium sulfate, and wash the separating funnel and the filter with  small portions of the diethyl 
ether.  
F.3.1.2.7  Evaporate the ether extract plus washings on a warm water bath. When the residue is just  dry, heat it 
rapidl y to 130 °C and immediately place the beaker in a desiccator to cool.   
©RSB 2021 - All rights reserved              16 
 NOTE  F.3.1.2.2 to F.3.1.2.7 should be completed in the shortest possible period of time, so as to prevent oxidation of the fatty acids.  
F.3.2 Determination of rosin content  
F.3.2.1 Weigh  accurately into a 150 mL flask with a ground -glass joint approximately 2 g of the  prepared fatty 
matter ( F.3.1.2.7) and reserve the rest in the case of soap powders for the fatty matter  titre determination.  
F.3.2.2 Add exactly 25 mL of the naphthalene -2-sulfonic acid solution to the flask and two or three  glass beads, 
and boil under reflux for 30 min.  
F.3.2.3 Carry out a blank test at the same time, using exactly 25 mL of the naphthalene -2-sulfonic  acid solution 
only.  
F.3.2.4 Cool the contents of both flas ks (sample and blank) to ambient temperature, add 0 .5 mL of  the 
phenolphthalein indicator to each flask, and immediately titrate to the end point with the  standard ethanolic 
potassium hydroxide solution.  
F.4 Calculation  
Rosin content of fatty matter, as a mass  fraction percentage ( R): 
01634.C. N)BA(R 
 
where  
A is the volume of the standard ethanolic potassium hydroxide solution used for the titration  of 
the sample solution, in millilitres;  
B is the volume of the standard ethanolic potassium hydroxide solution used for the titration  of 
the blank solution, in millilitres;  
N is the normality of the standard ethanolic potassium hydroxide solution;  
C is the mass of the fatty matter taken, in grams.  
 
 DRS 89: 202 1 
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 Bibliography  
[1] ISO/IEC Directives, Part  2, Rules for th e structure and drafting of International Standards , 2016  
[2] ISO/IEC  TR 10000 -1, Information technology  — Framework and taxonomy of International Standardized 
Profiles  — Part 1: General principles and documentation framework  
[3] ISO 10241  (All parts) , Terminological entries in standards  
[4] ISO 128-30, Technical drawings  — General principles of presentation — Part 30: Basic conventions for 
views  
[5] ISO 128-34, Technical drawings  — General principles of presentation  — Part 34: Views on mechanical 
engineering drawings  
[6] ISO 128-40, Technical drawings  — General principles of presentation  — Part 40: Basic conventions for 
cuts and sections  
[7] ISO 128-44, Technical drawings  — General principles of presentation  — Part 44: Sections on 
mechanical engine ering drawings  
[8] ISO 31 (all parts), Quantities and units  
[9] IEC 60027 (all parts), Letter symbols to be used in electrical technology  
[10] ISO 80000 -1, Quantities and units -- Part 1: General  
[11] ISO 690, Documentation  — Bibliographic references  — Content, form and structure  
 DRS 89: 202 1 
 
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