CH. x.] BANG'S METHOD. 257 



into cold water. Allow it to cool in a stream of water for at least 

 i minute. 



NOTE. A special pair of forceps has been devised for holding the flask 

 and sealing the rubber tube. 



5. Titration of the fluid. Loosen the clip, remove the rubber, 

 and immediately fit in the tube from the CO 2 apparatus, the gas 

 having previously been turned on. Add 3 or 4 drops of the starch 

 solution and titrate with N/2OO iodine from a microburette. The 

 titration is completed when the " starch-blue " tint persists for 

 about 20 seconds. 



6. Calculation. 



cc. of iodine 0-16 cc. 



= mg. of glucose in the blood taken. 



7. Example. 



Weight of blood = 118 mg. 

 Iodine required = 0-68 cc. 



0-68 0-16 0-52 , , T , 



- = - - = 0-13 mg. glucose in 118 mg. blood. 



4 4 



= o-ii per cent. 



NOTES. i. The results obtained are apt to be slightly higher than those 

 by Benedict's method, but the advantage of a " finger-prick " method of 

 drawing the blood is so great that it overweighs the possible slight error. It 

 is most important to use the purest chemicals obtainable and to pay strict 

 attention to details. 



2. Bang has recently published a new method of analysis (see p. 126, 9), 

 but the author, having failed to get consistent results with it, prefers to use a 

 method with which he is familiar. 



313. The micro-analysis of chlorides in blood by Bang's 

 method. 



Principle. A few drops of blood are taken up from a finger 

 prick on to a piece of absorbing paper. The proteins are coagulated 

 by pouring on a boiling acid solution of magnesium sulphate. After 

 cooling, 2 cc. of standard silver nitrate are added and the silver 

 chloride filtered off, a little kieselgur being added to aid filtration. 

 The silver nitrate in the filtrate is treated with 2 cc. of a standard 

 solution of potassium iodide and potassium iodate and a few drops 



s 



