Coloured analytical tables : showing the behaviour of the more common metals and acids to the ordinary reagents, with special reference to the colour of the various oxides, salts, precipitates, flames, borax-beads, and blowpipe reactions a class-book for students in hospitals, colleges and schools / by H. Wilson Hake.

  • Hake, H. Wilson (Henry Wilson), 1857-1930
Date:
1889
Catalogue details

Licence: Public Domain Mark

Credit: Coloured analytical tables : showing the behaviour of the more common metals and acids to the ordinary reagents, with special reference to the colour of the various oxides, salts, precipitates, flames, borax-beads, and blowpipe reactions a class-book for students in hospitals, colleges and schools / by H. Wilson Hake. Source: Wellcome Collection.

    35/40 (page 5)
    D. Test specially for the following organic acids :— 1. Acetates.—C,H302. In solution or solid, acetates yield on heating with dilute sulphuric acid, free acetic acid, recognized by its vincgar-likc smell; or, on heating with alcohol and strong sul- phuric acid, yield acetic ether, recognized by its fragrant odour. 2. Tartrates.—C4H4Og. Solid tartrates or strong solutions of tartrates or free tartaric acid blacken almost immediately when heated with strong sulphuric acid, giving off a smell of burnt sugar and of sulphurous anhydride (S02). Neutral tartrates yield a white precipitate with AgNOa, which, if nearly dissolved in ammonia, yields a brilliant silver mirror on the sides of the test-tube when gradually and gently heated. Calcium chloride gives a white pre- cipitate (CaC4H40G), soluble, after washing, in KIIO. 3. Citrates.—C(.II507. Solid citrates or strong solutions of citrates or free citric acid darken slowly, and yield pungent irritating fumes, with strong sulphuric acid. Calcium chloride in neutral solutions yields a white precipitate [Ca3(CGH.07)2] only on heating. E. Test specially for the following organic substances :— 1. Cane Sugar (C12H22On). Tastes sweet, and blackens on addition of strong sulphuric acid. Its solution does not reduce copper sul- phate (CuS04), except after boiling for some time with two or three drops of dilute hydrochloric acid (sec Grape Sugar). 2. Grape Sugar (C6H12O0). Tastes sweet, and, when pure, does not blacken, but becomes of a pale straw-colour on addition of strong sulphuric acid. Its solution reduces copper sulphate. (To make this test, add to a very dilute solution of cupric sulphate an excess of potash, and pour a little of the slightly turbid solution, so obtained, into a boiling solution of the grape sugar : a yellow-red precipitate of suboxide of copper (Cu.,0) indicates the reduction.) 3. Starch (CGIT10O5). With a little water it forms a gela- tinous mass on boiling; with much water a turbid solution, which, on addition of a solution of iodine, yields a fine blue colour. 4. Urea.—CO(NH2)2. White and crystalline, readily soluble in water and in alcohol. The aqueous solution, which is neutral to litmus, yields ammonia when boiled with potash, and, when concentrated, gives, with nitric acid, a highly crystalline precipitate of urea nitrate, C0(NH2)2, IINOa. Addition of sodium hypobromitc, NallrO (made by dissolving a few drops of bromine in concen- trated solution of caustic soda), causes a brisk evolution of nitrogen gas. Solid urea, heated on platinum foil, first melts and finally volatilizes, giving off ammonia at the same time. Urea nitrate and oxalate behave somewhat similarly, and the acids may be discovered in the ordinary way.