66 HEMOGLOBIN 



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 the iron 

 becomes insoluble. In both cases there will be a loss of iron." After 

 the "ashing" is complete the iron is dissolved in strong hydrochloric 

 acid, and a trace of hydrogen peroxide is added to ensure the complete 

 oxidation of the iron. The excess of hydrogen peroxide is subsequently 

 boiled off, and the titration with titanous chloride is made, potassium 

 sulphocyanide 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 analyses of iron such as have just been 

 described, he made from the same solution, run from the same 

 burette, sixteen oxygen estimations. These were divided into four 

 groups: the average of each group was taken and also the mean 

 of these four averages. The greatest error which entered into 

 Peters' blood-gas analysis was doubtless in the measurement of 3 c.c. 

 of fluid from an ordinary 50 c.c. burette, the meniscus in the case of 

 haemoglobin solution being none too well defined. This error, serious 

 though it appears, is discounted by the fact that the sixteen samples 

 for analysis were run consecutively out of the burette. There may be 

 a certain ruggedness in the individual figures, but the averages of 

 the groups of four are very close to one another, since a positive 

 error in one sample entails an equal negative error in the next: in 

 the aggregate 48 c.c. used there is no appreciable error as compared 

 with the 50 c.c. used by the iron analysis. 



Peters' figures for the oxygen are as follows : 



Oxygen in 3 c.c. of solution A in c.c. 



