A system of instruction in qualitative chemical analysis / by Dr. C. Remigius Fresenius .. ; edited by J. Lloyd Bullock, F.C.S.
- Carl Remigius Fresenius
- Date:
- 1855
Licence: Public Domain Mark
Credit: A system of instruction in qualitative chemical analysis / by Dr. C. Remigius Fresenius .. ; edited by J. Lloyd Bullock, F.C.S. Source: Wellcome Collection.
254/342 page 228
![y. Sulphuric acid is detected by means of chloride of barium in the hydrochloric acid solution filtered from the silicic acid, provided the tem- perature at which the separation of the silicic acid has been effected was not too high. S. If the silicic acid which has separated looks black, but becomes white upon ignition in the air, this indicates the presence of charcoal or of an organic substance. If organic substances are present, the silicate exhales an empyreumatic odor when heated in a glass tube. e To detect the boracic acid which may be present, fuse a portion of the substance in a platinum spoon with carbonate of soda and potassa, boil the fused mass with water, filter, and,— a. Add to a small portion of the filtrate hydrochloric acid until the reaction is distinctly acid, dip a slip of turmeric paper half into the fluid, and dry at a gentle heat. If boracic acid is present, the part of the slip which has been immersed in the fluid appears brownish-red.* b. Neutralize the remainder of the filtrate nearly with sulphuric acid, evaporate to dryness, and test the residue with alcohol and sulphuric acid, as directed § 136, 5. £. With many silicates boiling with water will suffice to dissolve the metallic chlorides present, which may then be readily detected in the filtrate by means of solution of nitrate of silver; but the safest way is to dissolve the mineral in dilute nitric acid, and test the solution with nitrate of silver. 7]. Metallic fluorides, which often occur in silicates in greater or smaller proportion, are detected by the methods described § 138, 6. b. Silicates which resist the action of hydrochloric acid, but are decom- posed by concentrated sulphuric acid. Heat the finely pulverized mineral with moderately concentrated pure sulphuric acid (best in a platinum dish), finally drive off the sulphuric acid, boil the residue with hydrochloric acid, dilute, filter, and treat the filtrate as directed § 178 ; and the residue, which, besides the separated silicic acid, may contain also sulphates of the alkaline earths, &c., according to the directions of § 191. * This method of detecting boracic acid, which JET. Rose gives in the additions and cor- rections to the first volume of his Manual, page 946, recommends itself equally by its simpli- city and delicacy. A solution of one part of borax in 1000 parts of water, acidified with hydrochloric acid,.imparts to turmeric paper, after drying, a distinctly brown tint. This method may, therefore, be employed advantageously also in the general course of analysis to effect the detection of minute traces of boracic acid, which might escape notice by the common method.](https://iiif.wellcomecollection.org/image/b28080361_0254.jp2/full/800%2C/0/default.jpg)
