254 J. M. Lewis : 



gations in the changes of hydrogen ion concentration in the 

 blood, was content to disregard it. He remarks that the error 

 must be small, since the measured e.m.f. varies only as the 

 logarithm of the partial pressure, and in his opinion its 

 recognition did not warrant the needless bleeding of the animal 

 involved in the method of Hasselbalch (5). 



Where it is thought absolutely necessary to eliminate this 

 source of error, recourse may be had to the Konikoff or Hassel- 

 balch electrode vessel. 



These vessels provide means whereby the specimen being 

 examined may be brought into contact with the hydrogen at- 

 mosphere above the electrode and shaken, thus allowing the 

 tension of the C0 2 in the hydrogen to become equal to that in the 

 fluid. After this has been done, the fluid is removed, and re- 

 placed by a fresh sample without changing the hydrogen 

 atmosphere. There will then be no further diffusion Of CO a 

 into the gas space, since conditions of equal tension will have 

 been established as regards any CO : 2 present. Incidentally, the 

 shaking of the electrode tube will have the effect of removing 

 . any oxygen present in the liquid, by combining it with the hy- 

 drogen of the electrode. This in itself will assist in obtaining 

 a constant e.m.f. in a comparatively short time. 



Preparation of the Hydrogen. 



The hydrogen used in these tests must be of extreme purity. 

 If it be prepared from dilute sulphuric acid and zinc in Kipp's 

 apparatus, there may be some danger of contamination with 

 hydrogen sulphide. M'ichaelis suggests that the gas be washed 

 with potassium permanganate solution, to remove any oxidis- 

 able substance, and then bubbled through a solution of mercuric 

 ■ chloride. (7) 



Sharp and Hoagland prepare the hydrogen by electrolysing 

 a 25 per cent by weight solution of caustic potash in a special 

 cell, using nickel electrodes. The hydrogen is led away, and 

 passed through a tube containing platinum black deposited upon 

 asbestos, which is kept hot by means of a glowing spiral of high 

 resistance wire electrically heated, the purpose of which is to 

 remove, as water, any oxygen which might be present. (6) 



In this laboratory, hydrogen, electrolytically prepared, and 

 stored in steel cylinders, is exclusively employed for saturating 

 the electrodes. 



