Manual of qualitative analysis / by Robert Galloway.

  • Galloway, Robert.
Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: Manual of qualitative analysis / by Robert Galloway. Source: Wellcome Collection.

    43/272 (page 25)
    dilute the solution obtained with just sufficient water to make the fluid appear of a light-blue colour. _ 43. Distilled water ought always to be employed in all the above solutions and in all analytical operations. It should leave no residue on evaporation, and should give no precipitate or even turbidity with chloride of barium, nitrate of silver, oxalate of ammonia, or lime water. 44. Reagent papers.—Blue litmus paper serves to detect the presence of free acids or of acid salts in fluids, since they change the blue colourto red. Reddened litmus paper serves to detect the presence of free alkalies,* and of earths and salts possessing an alkaline reaction, by changing the red colour to blue. Turmeric paper aids, like reddened litmus paper, in the detection of free alkalies, &c., by changing its yellow colour to brown. Preparation of blue litmus paper.— Digest one part of litmus of commerce with six parts of water, and filter the solution ; divide the intensely blue filtrate into two equal parts ; saturate the free alkali in the one part, by repeatedly stirring with a glass rod dipped in very dilute sulphuric acid, until the colour of the fluid just appears red ; add now the other part of the blue filtrate, pour the whole fluid into a dish, and draw strips of fine, unsized paper through it; suspend these strips over threads, and leave them to dry. The colour of litmus paper must be perfectly uniform, and neither too light nor too dark.” Preparation of reddened litmus paper.—“ Stir blue solu- tion of litmus with a glass rod dipped in dilute sulphuric acid, and repeat this process until the fluid has just turned distinctly red. Steep slips of paper in the solution, and * Dr. Taylor states that a very delicate test-paper for detecting alkalies may be prepared by steeping slips of paper in an acid infusion of rose petals. 2