Soda, Sulphite

Alternatively cellulose is produced from wood via wood pulp. A number of processes are used in which the overall effect is the removal of the bulk of the non-cellulosic matter. The most widely used are the sulphite process, which uses a solution of calcium bisulphite and sulphur dioxide, the soda process using sodium hydroxide and the sulphate process using a solution of sodium hydroxide and sodium sulphide. (The term sulphate process is used since sodium sulphate is the source of the sulphide.) For chemical purposes the sulphite process is most commonly used. As normally prepared these pulps contain about 88-90% alpha-cellulose but this may be increased by alkaline purification and bleaching. 

The sodium chloride and sulphate regularly found in Leblanc soda ash are not usually injurious the insoluble matter should not exceed 1 to 1J per cent. It consists principally of calcium carbonate, alumina, silica, and ferric oxide. The sulphides should not be detectable by lead paper thiosulphates are destroyed in calcining the ash sulphites are usually present and can be detected by iodine soln. and sodium hydroxide, except in the so-called caustic ash, does not usually exceed 1 per cent. The moisture in fresh ash ranges below one per cent. Owing to the mode of preparation, ash by Solvay s process is more pure than that prepared by Leblanc s process. It does not contain sodium hydroxide, sulphides, sulphites, or thiosulphates it may contain a slight excess of carbon dioxide a little sodium sulphate is always present iron, alumina, and silica are present in minute traces sodium chloride is perhaps the only... 

Whether a sulphite and hyposulphite actually exist is black ash, is a question that hardly admits of proof. They are included is the analyses of several investigators, and the researches of Mr. Kynaston certainly load to the B me conclusion. Still the probability of the formation of these, subsequent to the removal of the black ash from the furnace, ieso obvious, that until the point has been conclusively determined, it it better not to express any positive opinion. Blackest) liquors certainly contain both salts. Sulphate of soda and ferrocyanide of sodium are frequently constituents of block ash, hut these are not always present. The Editor has had numerous samples examined which were free from even a trace of either one or the other. The subjoined analyses of this highly complex mixture ore by Unqeb and EiCHABDSOrr. Both, it will be seen, assume the existence of a compound of sulphide of calcium and lime, and also of caustic sods. 

Properties.—Crystallized hyposulphite of eoda— Na 0, Ss Os, 5 HO—is an Inodorous salt with a taste first cooling, and afterwards bitter. The crystals are oblique prisms, belonging to the right prismatio system. They are deliquescent iu the air, but in vacuo lose their water of crystallization. When heated, the salt at first undergoes the aqueous fusion, and then dries up Into a white moss the heat being continued, it takes fire, bunting vividly and with a clear yellow fame. Hyposulphite of soda is readily soluble in water, but not in alcohol. In close vessels the aqueous solution deposits sulphur till nothing but sulphite of soda remains In the liquid exposed to the air it deposits sulphur, and the sulphite is converted into sulphate of soda. 

Sulphurous acid, in the shape of sulphite of soda, has. been an article of commerce for some time, under... 

The sulphites of potassa and ammonia may be prepared in a similar manner to that of soda, by passing sulphurous acid through a solution of the alkalies or their carbonates. 

Nitrososulphonic Acid or Nitrosohydroxylamine-sulphonic Acid, N(NO)(OH)SOgH or H02N2S03H.—The sodium salt of this acid has been prepared by the action of nitric oxide on a caustic soda solution of sodium sulphite 3... 

The separation of cellulose from the wood is carried out by one of three methods the soda process, the sulphate process, and the sulphite process. Nitration cellulose is prepared chiefly by the sulphite and sulphate methods. 

The first process was that of P. Spence and Sons1 in 1903, in which the sulphite was reduced by mixing it with titanium trichloride. The mixture was subsequently poured into caustic soda solution and stable sodium hydrosulphite formed, whilst the titanium was precipitated as titanic hydroxide Ti(OH)4. This hydroxide was afterwards dissolved in hydrochloric acid and reduced by electrolysis... 

Osmyl sulphites readily lend themselves to preparation in this manner. Rosenheim and Sasserath2 first prepared sodium osmyl sulphite by passing sulphur dioxide through a solution of osmium tetroxide in caustic soda. 

Cyanide. This should have been detected and confirmed in the preliminary test with dilute sulphuric acid (Prussian blue test or as Section IV.8, reaction 1). Sulphite. This anion will have been detected in the preliminary test with dilute sulphuric acid (potassium dichromate paper or fuchsin solution test). Hexacyanoferrate(II) (and Thiocyanate). Acidify 1 ml of the soda extract with dilute hydrochloric acid and add a few drops of iron(III) chloride solution. A deep-blue precipitate indicates hexacyanoferrate(II) present. Now add 0-5-1 ml iron(III) chloride solution, 0-2 g sodium chloride and half a Whatman filtration accelerator, shake the mixture vigorously and filter. A deep-red filtrate indicates thiocyanate present. 

Sulphide, cyanide, and sulphite. Acidify 10 ml of the soda extract with dilute acetic acid and boil gently for 3-4 minutes make certain that the solution remains acid (e.g. to litmus) throughout. If sulphite is present, it is advisable to heat the solution for 10-15 minutes (maintaining the volume, if necessary) whilst a stream of air is drawn through it (cf. Fig. IV.2) test for complete removal of sulphur dioxide with fuchsin solution. 

Hexacyanoferrate(II) and (III). Employ the original solution from 1 or, if sulphide, cyanide, and sulphite are absent, use 10 ml of the soda extract made acid (to Congo red) with dilute acetic acid. Add 0 5m zinc nitrate solution until precipitation ceases, introduce a Whatman filtration accelerator, stir, and filter the zinc and hexacyanoferrate(II) and (III) in the cold wash with a little O 1m zinc nitrate solution. 

The test may also be conducted with 2 ml of the soda extract. Carbonate, sulphite, and thiosulphate have no influence upon the reaction. Nitrite interferes, presumably owing to the oxidation of the hydrogen cyanide. In the presence of sulphide, the test is complicated by the precipitation of black iron(II) sulphide when sulphate is added to the alkaline solution. It is best to boil the solution containing the suspended iron(II) sulphide, acidify with hydrochloric acid, and boil again to expel most of the dissolved hydrogen sulphide upon adding a drop of iron(III) chloride solution, a blue precipitate is produced if cyanide is present. 

The presence of iodate in the soda extract can be readily detected as follows. Treat 2 ml of the solution with silver nitrate solution until precipitation ceases, heat to boiling for 2-3 minutes and filter. Render the filtrate strongly acid with hydrochloric acid, add 2 ml of 0-5m iron(II) sulphate solution (or 0 5m sodium sulphite solution) and shake it with 2 ml carbon tetrachloride. A purple colouration of the organic layer indicates iodate. 

Tests with silver nitrate solution -Sulphide, cyanide, and sulphite interfere in tests with silver nitrate solution, hence if any of these anions was detected in the preliminary test with dilute sulphuric acid, it must be removed first as follows. Acidify 1 ml of the soda extract with dilute acetic acid (use litmus paper) and boil gently in a small conical flask or crucible in the fume cupboard to expel H2S, HCN or S02 (1-2 minutes). It is important that the solution be acid throughout. Centrifuge, if necessary, and allow to cool. If the volume has been reduced appreciably, add water to restore the original volume. 

Solution. Dissolve 100 gm. of the commercial lump caustic soda in 1000 cc. of water. Use an iron dish, and add the solid slowly to the liquid with constant stirring. Filter through glass wool or shredded asbestos. Keep tightly stoppered. Sodium Sulphite, Na SOs. — Dissolve 200 gm. of the crystallized commercial salt in 1000 cc. of water. Stannous Chloride, SnClo. — (i) Use the commeicial solution. 

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