The respiratory function of the blood / by Joseph Barcroft.

  • Barcroft, Joseph, 1872-1947.
Date:
1914
Catalogue details

Licence: Public Domain Mark

Credit: The respiratory function of the blood / by Joseph Barcroft. Source: Wellcome Collection.

    23/344 (page 5)
    individual analyses, if theoretically somewhat more accurate, extended over two or three days and entailed the use of large quantities of haemoglobin. It was impossible in their case to obtain large numbers of analyses which could be averaged and from which the errors could be eliminated to some extent by statistical treatment. In estimating the iron by titration with titanium advantage has been taken of new methods of analysis which are much simpler and more accurate than the older permanganate titrations. The theory of the titanium method of estimating iron is repre¬ sented by the following equation : TiClg + FeCl3 = TiCl4 + FeCl2. The method has this great advantage over that of titration with potassium permanganate, that it is not vitiated by the presence of chlorides. In practice defibrinated blood was centrifugalised, the corpuscles washed twice in isotonic salt solution, and as much as possible of the fluid was got rid of. The cream of corpuscles was laked by the addition of twice its volume of dilute ammonia (4 c.c. of strong ammonia per litre). This solution, which we shall call solution A, was centrifugalised again to rid it of any corpuscles which did not lake and of other debris. Portions of it were then measured out from the same burette, both for the iron estimations and the oxygen analyses. For the former 50 c.c. of the solution was evaporated in a platinum crucible and carefully “ashed.” It was at this point that the nicety of the determinations really entered if accurate results were to be obtained. The ashing must take place at a temperature which is neither too hot nor too cold. It is best carried out in a “muffle furnace.” To quote Peters, “ If the carbon is not completely burned away iron will still remain which cannot be removed by boiling with acids ; whereas on the other hand if the ash is heated to a high temperature in removing the carbon the iron becomes insoluble. In both cases the result will be a loss of iron.” After the ashing is complete the iron is dissolved up in strong hydrochloric acid, and a trace of hydrogen peroxide is added to insure the complete oxidation of the iron. The excess of hydrogen peroxide is subsequently boiled off and the titration with titanous chloride is made, potassium sulpho- cyanide being used as an indicator. Some idea of the scale on which Peters’ experiments were con¬ ducted may be gleaned from an account of a single experiment. In addition to making two or three analyses of iron such as have just been