The use of litmus paper as a quantitative indicator of reaction / by G.S. Walpole.

  • Walpole, George Stanley.
Date:
1913
Catalogue details

Licence: In copyright

Credit: The use of litmus paper as a quantitative indicator of reaction / by G.S. Walpole. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    Preliminary observations in 'protein solutions. In solutions of protein, peptone and the like the use of litmus paper has, as far as my experience goes, always indicated the solution to be more alkaline than it really is. For instance an acid 4 per cent, solution ol Witte peptone containing 1 per cent, ol sodium chloride, and 1 c.c. per cent, of normal hydrochloric acid was found by electric measurement to have Pj= 6'5. In a tintometer arranged to compensate for the colour of the Witte peptone [Walpole, 1910] and using neutral red as indicator, the P,1, value was made out to be the same as that of a phosphate mixture P=6,81. A neutral N/15 phosphate solution was prepared (Pu = 7'07) and a comparison instituted between this solution and the acid Witte peptone solution above. It will have been noticed that neither contains a volatile constituent. Three papers were taken (No. 4 red, No. 2 blue and No. 3 red) and one slip of each paper dropped into a large volume of each fluid. They were removed at intervals, laid on white paper and examined in diffused daylight. The unglazed, quickly-reacting paper (No. 4 red) gave with the acid peptone solution a bluer tinge almost at once than the corresponding paper in the phosphate solution and this relation continued indefinitely. The blue paper No. 2 was always bluer in the acid peptone solution: the red paper No. 3 lost most of its colour in the phosphate solution before the progressively bluer paper in the acid Witte peptone solution could match it. In another case a faintly alkaline 4 per cent, solution of Witte peptone of reaction P£ = 7'3 gave with papers No. 2 (red and blue), No. 3 (red and blue), No. 4 (red and blue) the same equilibrium tint, as nearly as could be judged, as any of the ammonia-ammonium chloride dilutions examined, which had Ph = 8T in each case. Examples. By neglecting to consider these secondary influences it is possible to obtain some bewildering results. For instance we may take two alkaline solutions having the same reaction, P/, = 8T; A is a solution of ammonium chloride and ammonia, 3N with respect to the former and 3/32 N with respect to the latter; B is this solution diluted 32 times and the “reaction inertia” of A is about 30 times that of B ; C is a neutral phosphate solution; 1 In the same apparatus using litmus tincture as indicator no real match could be obtained but the indications were that the peptone solution was more alkaline than a phosphate mixture K=9-