The specific oxygen capacity of blood ."> 



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 : 



TiCl, + FeCl 3 = TiCl 4 + FeCl 2 . 



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 



