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The Fundamental Processes Of Dye Chemistry | by Dr. Hans Eduard Fierz-David



Although well aware of the existence of a large literature dealing with laboratory practice, I have written this book because there does not appear to exist a suitable introduction to the fundamental operations of dye chemistry. Ignorance of elementary facts leads in practice to waste of time, which may be redeemed in part by suitable instruction; nor should it be forgotten that many of the essential features of chemical craft may be learnt from books. The manufacture of synthetic colours has attained to such importance that it seems desirable to familiarize the rising generation of chemical technologists with the methods of production of the more important intermediates. With this end in view, I have attempted a description of these methods in a manner which may be helpful even to those unfamiliar with technical operations.

TitleThe Fundamental Processes Of Dye Chemistry
AuthorDr. Hans Eduard Fierz-David
PublisherD. Van Nostrand Company
Year1921
Copyright1921, D. Van Nostrand Company
AmazonThe Fundamental Processes of Dye Chemistry

By Dr. Hans Eduard Fierz-David Professor Of Chemistry At The Federal Technical High School, Zurich

Translated By Frederick A. Mason, M.A. (Oxon.), Ph.D. (Munich) Research Chemist With The British Dyestuffs Corporation, Limited.

With 45 Illustrations, Including 19 Plates

-Preface To The English Edition
In preparing an English edition of Prof. Fierz-David's well-known work on the practical side of dye chemistry, advantage has been taken of the opportunity to correct one or two slight errors that had ...
-List Of Figures And Plates
Fig. Plate Page 1. I. Laboratory autoclave with stirrer . . Frontispiece 2. Sulphonating pot for naphthalene sulphonic acid . . 5 3. Fusion pot for -naphthol ...... 8 4. Autogeneously welded...
-Introduction
Although well aware of the existence of a large literature dealing with laboratory practice, I have written this book because there does not appear to exist a suitable introduction to the fundamental ...
-I. Intermediate Products. General Considerations
The term Intermediate Products is applied, in the dye industry, to those substances obtained from organic products, whether aromatic or aliphatic, which are devoid of dye character. The most important...
-1. Sulphonations
-Naphthalene-monosulphonic Acid and -Naphthol. Reaction: This product may be prepared by several different methods. If the -monosulphonic acid is to serve for the preparation of...
-1. Sulphonations. Part 2
The yield of -salt is about 165 %, calculated on the weight of naphthalene taken, which corresponds in this case to a yield of 400-420 gms. The mother-liquors can be worked up for Glauber's s...
-1. Sulphonations. Part 3
The crude product is quite adequate for most purposes, but for sale it must be carefully purified owing to the very high standard required. At the present day vacuum distillation only is made use of (...
-1. Sulphonations. Part 4
280 gms. H2So4 (100 %). Fig. 6. - Sulphonating and nitrating pot in wooden tub for heating or cooling. Fig. 7. - Sulphonating and nitrating pot with steam-jacket. Plate II. works has a much ...
-1. Sulphonations. Part 5
The removal of the excess of sulphuric acid may be effected by the use either of slaked lime or of pure, finely powdered chalk. It will be found that calcium carbonate is the most convenient, as it gi...
-1. Sulphonations. Part 6
As soon as everything is ready, the iron turnings are boiled up for five minutes, the nitro acid made faintly acid to Congo, and the latter solution is then allowed to drop in slowly through a droppin...
-1. Sulphonations. Part 7
28 Nitrite trisulph. acid. 130 gms. NaOH. 130 gms. Water. Total wt. about 540 gms. It is, however, preferable to allow the precipitate to stand for a few hours, to ensure that the separation is compl...
-1. Sulphonations. Part 8
As a general rule, it may be noted that the melts of all sulphonic acids only go well when the salt content of the starting material is very slight; salt is practically a poison for alkali fusions, as...
-1. Sulphonations. Part 9
103 gms. Hno3 (60 % = 400 Be.) = 1 mol. Plate III. Fig: 8. - Hydraulic press and pump with automatic cut-out (made by Bucher-Mauz, Niederweningen, Canton Zurich). 1. Cast-steel cylinder. 2. Platf...
-1. Sulphonations. Part 10
The temperature rarely rises above 35o, for which reason it is necessary to use pure monohydrate, or else part of the naphthalene will remain unattacked. In any case, however, it will be found that a ...
-1. Sulphonations. Part 11
1:5 acid will be carried down with it). Both methods appear, however, to be of about the same value. The 1:8-naphthylamine sulphonic acid or peri-acid is not used directly as such for the preparation...
-1. Sulphonations. Part 12
If it is desired to obtain more R-acid than Schaffer acid the quantity of sulphuric acid is increased, so that finally 2:3:6-naphthol-disulphonic acid is obtained almost exclusively. Yield: 160 gms....
-1. Sulphonations. Part 13
192 Gms. of the sulphate (=1 gm.-mol.) is ground up very fine, well rubbed up with 1 gm. of calcined soda, and then added to 560 gms. of sulphuric acid monohydrate at a temperature of 30-60o. It is ...
-1. Sulphonations. Part 14
The pure sulphonic acids are distinguished by a very characteristic fluorescence, which can, however, only be seen clearly with very pure products, as otherwise they are hidden by the fluorescence of ...
-1. Sulphonations. Part 15
35 gms. Nitrite. 2:5:7-Naphthyl-amine disul-phonicacid. ca. 180 gms. 220 gms. NaOH. 160 gms. H2O. Nitrobenzene Sulphonic Acid and Metanilic Acid from Nitrobenzene. Reaction: Sulphone. 1 Gm.-m...
-Sulphanilic Acid. Bake Process
So far we have only examined cases of sulphonation where the liquid was kept in motion by means of a stirrer. There is, however, another method of sulphonating, which is based on a quite different ide...
-Other Methods Of Sulphonation
In addition to sulphuric acid certain other sulphonating agents may be made use of, although they play no very important part in dye technology. The use of chlor-sulphonic acid as a sulphonating agent...
-Preparation Of An Amino-Naphthol Sulphonic Acid From The Corre Sponding Hydroxy-Nitroso Compound (Quinone Monoxime)
1:2:4-Amino-naphthol Sulphonic Acid from -Naphthol. 1. Nitroso--naphthol. - 1oo gms. of -naphthol1 are dissolved in 90 gms. of 35 % caustic soda lye and 1 litre of water at 500, con...
-2. Nitrations And Reductions
Nitrobenzene.1 Reaction : The chief condition to be observed in the manufacture of nitrobenzene is the correct and intimate mixture of the components; if this is done it is easy to obtain good yi...
-Aniline From Nitrobenzene
Reaction: For the preparation of aniline from nitrobenzene we use an autogenously welded iron reaction vessel, such as is shown in Fig. 4 (p. 11),1 This apparatus is provided with a condenser and ...
-Benzidine From Nitrobenzene
Reaction: Phenylhydroxyl-amine. Azoxybenzene. Azobenzene. Benzidine {cm. 85 %). Diphenyline. (ca.15 %). Nitrobenzene is reduced to hydrazobenzene by means of cast-iron borings (in strong c...
-Reduction To Hydrazobenzene
Reduction by means of Zinc Dust. - 91 gms. (= 1/2 mol.) azobenzene is heated up with 250 gms. alcohol and 200 gms. soda lye (30 % NaOH) to 450 in an iron or glass vessel provided with a powerful stirr...
-Reduction To Hydrazobenzene. Continued
55 gms. H2So4, 66 B6. 50 gms. Na2Co3. The apparatus used on the works must be built very strongly as the stiff iron mass offers very great resistance to stirring. Plate XL, Fig. 29, illustrates...
-Phenylhydrazine Sulphonic Acid From Sulphanilic Acid
Reaction: 3/10 Gm.-molecule technical sulphanilic acid (100 %) is dissolved in 200 c.cs. water with the aid of 16 gms. of soda, the residual aniline being boiled off with steam. The filtered solut...
-Phenylhydrazine Sulphonic Acid From Sulphanilic Acid. Continued
Other nitro compounds must be reduced in ammoniacal solution with exactly the calculated quantity of hydrogen sulphide. It happens frequently that mere careful weighing of the hydrogen sulphide is ins...
-Acetanilide
186 Gms. of purest aniline are heated with the same volume of 100 % (glacial) acetic acid in a bolthead of 1/2 litre capacity. Highly concentrated acetic acid has a strong action on most metals, for ...
-Amino-Acetanilide From Nitro-Acetanilide
This azo component is prepared by the neutral reduction of nitro-acetanilde in practically the same way as has already been described several times. In an iron beaker provided with a propeller stirrer...
-Amino-Acetanilide From Nitro-Acetanilide. Continued
Fig. 16. - Small gas cylinder made of gas-tube for adding alkyl chloride. water, 1 gm.-molecule caustic soda lye, and 80 gms. soda. To this solution are added 500 c.cs. methyl (or ethyl) alcohol of 9...
-Picramic Acid
Reaction: 10 Gms. picric acid and 10 gms. of 35 % soda lye are dissolved in 600 c.cs. water contained in a glass or iron vessel holding at leas' 1 1/2 litres. After heating up to 550 the liquid is...
-3. Chlorinations. Chlorbenzene And Dinitrochlorbenzene From Benzene
Reaction: On the works scale the introduction of chlorine and bromine into aromatic hydrocarbons is carried out almost exclusively by direct halogenation. Only in very special cases is the Sandmey...
-Dinitrochlorbenzene From Chlorbenzene
The nitration of chlorbenzene takes place very readily; it is nitrated first only to the mono-nitro stage, as given under the preparation of dinitrobenzene. The product is a mixture of ortho- and para...
-Benzalchloride And Benzaldehyde From Toluene
Reaction: 1 For manufacture, cf. Zeitschr. f. das Gesamte Spreng und Schiesswesen (1913), 8, 205 and 251 (Carter). 2 Picric acid may also be prepared via picryl chloride. Benzaldehyde. Be...
-Benzalchloride And Benzaldehyde From Toluene. Continued
(b) 2:6-Chlortoluidine. The reduction of nitrochlortoluene is done by Bechamp's method. 100 Gms. of the nitro compound are added during 2 hours to 100 gms. finely divided iron, 20 gms. crude hydrochl...
-4. Oxidations
Dinitrostilbene-Disulphonic Acid and Diaminostilbene-Disulphonic Acid from p-Nitrotoluene. (Conjoint oxidation of two molecules.) Reaction: 1 Cf. also Malachite Green and Xylene Blue VS. (a) ...
-Anthraquinone From Anthracene
Reaction: Anthracene. Anthraquinone. The anthracene used for the preparation of anthraquinone should not be too impure, or too much chromic acid will be used up. At the present day, the tar dist...
-5. Condensations. Diphenylamine From Aniline And Aniline Salt
Reaction: 93 Gms. aniline and 93 gms. aniline hydrochloride (aniline salt) are heated for 20 hours to 230 in an enamelled autoclave fitted with an enamelled thermometer tube. The pressure rea...
-5. Condensations. Diphenylamine From Aniline And Aniline Salt. Continued
144 gms. -Naphthol. 600 gms. (Nh4)2So3 (22 %). 125 gms. 20 % Nh3. no gms. 30 % Hc1. 1 1/2 litres H2O, 200 gms. Na2So4. 1 Ammonium sulphite is obtained by saturating 250 gms. of 20 % ammonia w...
-Salicylic Acid From Phenol
Reaction: Phenol. Salicylic acid. At the present day salicylic acid is made exclusively by the Kolbe-Schmitt method, which consists in treating sodium phenate with dry carbonic acid at first at ...
-Gallamide And Gallic Acid From Tannin
Reaction: Tannin or other tanning material. Gallic acid. Gallamide. 1 D. R.P. 65131 (1892). 2 It is dissolved in soda, the boiling solution piecipitated with hydrochloric acid, and the liquid ...
-II. Dyes. 6. Azo Dyes
As the azo colours form at the present day by far the largest group of synthetic organic colouring matters, I have prefaced the sections dealing with these products by certain general methods, as in m...
-Aniline
(Toluidine; Xylidine; Meta-nitraniline.) 9.3 Gms. (1/10 mol.) aniline are stirred up by means of a glass rod with 30 c.cs. hot water and 25 c.cs. concentrated hydrochloric acid are then added in a th...
-Sulphanilic Acid. Metanilic Acid, Naphthionic Acid, Nitraniline Sulphonic Acids, Chloraniline Sulphonic Acids, Diamino-Stilbene Disulphonic Acid, Primuline Sulphonic Acid, etc
17.3 Gms. (1/10 mol.) 100 % sulphanilic acid are dissolved in 100 c.cs. of water with the aid of 5.5 gms. soda.1 25 C.cs. hydrochloric acid are added and the whole diazotized with 35 c.cs. 20 % sodium...
-Benzidine, o-Tolidine, o-Dianisidine
18.6 Gms. (1/10 mol.) of technically pure benzidine are dissolved in 23 c.cs. of 30 % hydrochloric acid and 100 c.cs. water at 700.2 The solution is cooled to 30-400 when 50 gms. ice are added, a port...
-Benzidine, o-Tolidine, o-Dianisidine. Continued
Notes on Works Technique and Practice. - Owing to its cheapness and brilliant shade, Acid Orange A is one of the most widely used monoazo dyes. In the works the coupling is carried out in very large p...
-Benzidine Colours
Benzidine may be combined with all the phenols and amines which are used for the production of azo colours. It has been found that only one of the two azo groups of tetrazo-benzidine reacts vigorously...
-The Intermediate Compound Of Benzidine With Salicylic Acid
(o-Tolidine o-Cresotinic Acid.)1 18.6 Gms. (1/10 mol.) commercial benzidine are tetrazotized as described on p. no. The clear tetrazo solution is poured rapidly into a solution of 15 gms. pur...
-The Intermediate Compound Of Benzidine With Salicylic Acid. Part 2
The colouring matters from both phenylene and toluylene diamines are used in large quantities for the production of mixed shades. Diamine Green B (Cassella). Formula: 14.5 Gms. pure p-nitranilin...
-The Intermediate Compound Of Benzidine With Salicylic Acid. Part 3
Example of the combination, in presence of Mineral Acid, of an Amine which couples readily, with an Amino-naphthol sulphonic acid which couples with difficulty: Direct Deep Black EW (Bayer). Formula...
-The Intermediate Compound Of Benzidine With Salicylic Acid. Part 4
11 gms. pure m-Phenylene diamine. 10 gms. Na2C03. 120 gms. NaCl. 20 c.cs. conc. Hc1. Congo Red. 18.6 Gms. of commercial benzidine are diazotized as described on p. no, and this solution mixed ...
-The Intermediate Compound Of Benzidine With Salicylic Acid. Part 5
Diphenylamine. Orange IV or Tropaeoline. 52 Gms. (3/10 mol.) 100 % sulphanilic acid are dissolved in 16 gms. soda and 300 c.cs. of water, any excess of aniline being boiled off. The solution is filt...
-Aminoazobenzene From Aniline
Reaction: Diazoaminobenzene. Aminoazobenzene. 250 Gms. aniline are mixed with no c.cs. concentrated hydrochloric acid in a glass or porcelain beaker with good stirring, after which it is cooled ...
-Aminoazobenzene From Aniline. Continued
100 gms. Aminoazobenzene Hc1. 100 gms. Dinitrochlorbenzene. 250 gms. Na Acetate. 600 gms. 90% Alcohol. Fast Light Yellow G (Bayer). Bayer's Fast Light Yellow G is the simplest member of the Pyra...
-Chrysophenine Goo
Reaction: Brilliant Yellow. Chrysophenine Goo. 34 Gms. (1/10 mol.) of 100% diamino-stilbene-disulphonicacid is dissolved in 11 gms. sodium carbonate and 200 c.cs. water, and after cooling the...
-Chrysophenine Goo. Continued
A - N2 - B - N2 - C - N2 - D {e.g. Naphthogene Blue 4R; the combination Naphthylamine-disulphonic acid-2:4:8 - Cleve acid-17 - Cresidine - p-Xylidine) dye cotton more or less well without the aid of ...
-7. Triphenylmethane Dyes
Formula.1 (a) Leuco-Malachite Green. 37.8 Gms. (3/10 mol.) dimethylaniline, 24 gms. (2/10 mol.) 30 % hydrochloric acid, and 10.6 gms. (1/10 mol.) benzaldehyde are placed in a 300 c.c. bolthead an...
-7. Triphenylmethane Dyes. Continued
Sandmeyer was the first to recognize the connection between constitution and stability to alkalis, and his Erioglaucine, the formula of which is given below, was the first colour to be prepared in ...
-8. Sulphur Melts
Primuline (Green), Chloramine Yellow FF (Naphthamine Yellow NN) and Thiazole Yellow, from p-Toluidine. Generally speaking sulphur reacts with aromatic amines to give substitution products, two aroma...
-8. Sulphur Melts. Continued
It may also be noted that by alkylating Primuline handsome yellow basic and acid dyes are formed which have not, however, any great importance. Naphthamine Yellow NN. Formula: Dehydrothiotoluidine-...
-Sulphur Black T From Dinitrochlorbenzene
Reaction: Dye of unknown constitution. 70 Gms. dinitrochlorbenzene are heated to 900 with stirring in a glass or iron vessel with 120 c.cs. of water, and to it is added during 2 hours 108 gms. of...
-9. Miscellaneous Dyes
Indigo (Traugott Sandmeyer's Method).1 Although Sandmeyer's Indigo synthesis is no longer worked, it affords such a classical example of the co-operation between science and technology that an accoun...
-9. Miscellaneous Dyes. Part 2
200 gms. Hydrocyancarbodiphenylimide. 35 gms. H2S. 460 gms. 20% Nh3. 25 gms. S. (d) a-Isatin~anilide. The ring-formation giving isatin derivatives only occurs under certain very definite ...
-9. Miscellaneous Dyes. Part 3
45 gms. NaOH +H2S. 6 litres Ice+water. About 30 gms. Na2Co3. may again become of importance, since the discovery by Frasch of the great sulphur deposits in Louisiana and the electro-thermal prepa...
-Gallamine Blue From Gallamide
By heating nitroso-dialkylamines with gallic acid or its amide, well-defined compounds are obtained which are termed Oxazines. The gallic acid is obtained exclusively from natural tannin. Reaction: 2...
-Methylene Blue From Dimethylaniline
The formation of Methylene Blue is of interest both from the scientific and technical standpoints, and will therefore be discussed before the actual methods of preparation are described. Nitroso-dime...
-Methylene Blue From Dimethylaniline. Continued
Owing to its very pure shade and low price, Methylene Blue is highly valued, and is much used for dyeing tannined cotton. For silk printing the zinc-free Methylene Blue is used for the production of d...
-Mixture Of Aminoazo- Toluene And Aniline
54 Gms. o-toluidine (1/2 mol.) are mixed with 24 gms. aniline and then treated with 35 gms. of 30 % Hc1. The mixture is cooled externally to 15o and diazotized at this temperature during 2 hours, with...
-Mixture Of Aminoazo- Toluene And Aniline. Continued
I will give a few typical examples in order that the would-be colour-chemist may gain some idea of the importance of this aspect of the problem. In the short descriptions which have been given in this...
-10. Summary Of The Most Important Methods Used In The Preparation Of Synthetic Dyes
Sulphonations* 1. An aromatic substance is treated with concentrated sulphuric acid. 2. An aromatic substance is treated with sulphuric acid containing sulphur trioxide (Oleum). 3. By heating the a...
-III. Technical Details. 11. Vacuum Distillations In The Laboratory And In The Works
The process of distilling under reduced pressure, commonly called Vacuum Distillation, is one of the most important operations in colour technology. Certain products are distilled under reduced pressu...
-Vacuum Distillations In The Laboratory And In The Works. Continued
With such large apparatus several thermometers are required; one goes to the bottom of the still, thus permitting the temperature of the crude mixture to be ascertained, so that it is possible to reco...
-12. Notes Upon The Construction And Use Of Autoclaves
Autoclaves or pressure vessels are always used in cases where it is necessary to raise the temperature of a substance above its boiling point, or where gases are evolved on heating, which are necessar...
-12. Notes Upon The Construction And Use Of Autoclaves. Part 2
For the reasons just given, it is always desirable to heat the autoclave, whenever possible, in a suitable bath. Such a bath may contain either oil or solder. Even when no crusts are formed, which wou...
-12. Notes Upon The Construction And Use Of Autoclaves. Part 3
Autoclaves are generally erected in tall, well-lighted sheds provided with a travelling crane. Plate VII shows in section the interior of a colour shed with the adjoining autoclave shed. It may be see...
-13. Structural Materials Used In Dye Chemistry
The destructive action of chemicals makes the nature of the structural material used in the dye industry a matter of prime importance. From time to time it becomes necessary to decide what material is...
-1. Metals Used In Dye Chemistry
Iron is the most important structural material used in dye chemistry, and is utilized in every variety and form. In the form of cast iron it is used for sulphonating- and nitrating-pots, for evaporat...
-2. Non-Metals Used In Dye Chemistry
The most important of the inorganic materials are cement and stoneware. Where complete resistance to acid is required, stoneware is the only material which can be used. Occasionally, indeed, its plac...
-3. Structural Materials of Organic Origin Used In Dye Chemistry
The most important material of natural origin is, of course, wood. It is used for the vats employed in the manufacture of colours, for agitators, scaffolding, and, above all, for the construction of t...
-14. Technical Notes On Works Management
As compared with other industries, the value of the entire world-production of dyes is very slight, its worth in 1913, 20,000,000, not equalling a tenth part of the value of the wool crop, nor a fift...
-14. Technical Notes On Works Management. Part 2
Further, at this stage it is decided whether a reaction or a compound shall be patented. It is the task of the patent department to decide as to the likelihood of obtaining a patent or whether, if the...
-14. Technical Notes On Works Management. Part 3
Fig. 44. - Colour mixing machine with automatic device for filling and emptying (Hoechst system). Plate XVIII. The provision of air for a dye works is therefore a considerable item of expenditure...
-15. Example Of The Costing Of A Simple Dye
Orange II = Acid Orange A. (Sulphanilic Acid - -Naphthol; see p. 113.) The costing of the product of the dye factory is always done by the Costing Department. This department obtains daily, we...
-Alkali Melt Of Sodium Salt
In actual practice large amounts (from 400 to 2000 kilos, of the sodium salt) are melted, but to simplify the calculation we will assume that we are dealing with a charge of only 100 kilos. ...
-Sulphanilic Acid
(a) Nitrobenzene: Fr. 100 kgs. Benzene at 32 cts. ...... 32.00 110 kgs. Hno3 (75 %) at 40 cts, ...... 44'00 170 kgs. K2So4 2.70 frs. ...... 4.60 ...
-Preparation Of The Dye From Sulphanilic Acid And Naphthol
We will take the kilogram-molecule for our unit, and for this purpose we multiply up the Acid Orange charge given on p. 113 by 10,000. Fr. 173 kgs. Sulphanilic acid at 70 cts. per ...
-IV. Analytical Section. 16. Analytical Details
The exact determination of the composition and degree of purity of the raw and intermediate materials used for the production of dyes is of the greatest importance. The methods in use are partly physi...
-Preparation Of Standard
Sodium nitrite is generally estimated in commerce by oxidation with permanganate in the usual manner, but this gives values which are slightly too high for the works chemist. Besides the nitrous acid ...
-Preparation Of Pure Sulphanilic Acid
250 Gms. of commercial sulphanilic acid are dissolved in sufficient sodium carbonate to give a strongly alkaline solution, which is boiled until all aniline has disappeared. The volume is about 1 ...
-Preparation Of Normal Nitrite Solution (N.NaNo2)
75 Gms. commercial sodium nitrite are dissolved in a little water, filtered, and made up to 1 litre at 17.5. 50 C.cs. of the normal sulphanilic acid solution are then titrated with it in the foll...
-Preparation Of N/10 Phenyldiazonium Solution
50 C.cs. of aniline solution are measured out, treated with 50 c.cs. concentrated hydrochloric acid, and the mixture cooled by standing the measuring flask in ice water. 50 C.cs. N-nitrite solution ar...
-Estimation Of Amines
(a) Direct Estimation. The method consists in titrating the amine in very dilute solution with hydrochloric acid and sodium nitrite, the resultant diazonium solution being then coupled up with an exa...
-Estimation Of Naphthols
fi-Naphthol 1.42 Gms. (=1/100 mol.) naphthol are dissolved in 2 c.cs. caustic soda-lye of 30 % strength, and 25 c.cs. of 10 % sodium carbonate solution are added. Ice-cold diazobenzene solution is th...
-Aminosulphonic Acids
1/100 Molecule of the acid is dissolved in the requisite amount of sodium carbonate solution, which is then diluted to 250 c.cs., 25 c.cs. concentrated hydrochloric acid are added and the whole titrat...
-Estimation Of Aminonaphthol Sulphonic Acids
Two different determinations are always made. First of all the amount of nitrite required is measured and this figure is termed the Nitrite figure. Then the amount of diazonium solution needed is de...
-Test Papers
(1) Red and blue Litmus paper. - This is used as an indicator for all weak and strong bases and acids. It is turned red by acids and blue by alkalis. Preparation: Best quality litmus should be used. ...
-Solutions Of Reagents Used For "Spotting " On Filter-Paper
(1) H-acid solution. - 1 %, with 5 % sodium carbonate. This solution is used to indicate the presence of easily coupling diazo compounds in the rim of spots on filter-paper. In place of H-acid, R-salt...
-Evaluation Of Zinc Dust
1 Gm. of zinc dust and 4.00 gms. sodium bichromate are dissolved up, and the solution made up to a litre with the addition of 20 c.cs. of 20 % sulphuric acid. 250 C.cs. of this solution are taken and...
-Evaluation Of Lead Peroxide Paste
About 3-5 gms. of a good average sample of the paste is weighed out accurately between two watch glasses. 5 Gms. of Mohr's salt is then added, and the whole rinsed into a 200 c.c. flask. The mixture i...









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