292 Appendix I. On methods 



The clove oil is put in the following way. Starting with clean apparatus, the 

 taps of which are free from grease, a fine pipette is 

 drawn out which will go down the broad portion of the 

 tubing in the vicinity of the tap, the stopper of the tap 

 being removed. The stopper on the other side is turned 

 so that no air can get out of the manometer on that 

 side. The pipette is charged with clove oil, of which 

 some slight excess is put into the broad portion of the 

 tubing, the pipette is then removed, the tap on the 

 other side is opened gently and sufficiently to allow of 

 the oil descending the fine tubing and getting just 

 round the bend of the manometer ; the tap is then 

 closed again. 



All excess of oil is now removed from the broad F IG _ 137. 



portion of the tubing with a pipe cleaner. It is necessary 



that this should be done very thoroughly, as any oil which remains here is apt to 

 creep down and enclose a column of air in the manometer at a later stage. When all 

 excess of oil has been removed the tap may be opened and the oil allowed to find its 

 own level. 



Should bubbles form in the apparatus they may be expelled by forcing the fluid 

 up to the top on that side. This may be done by putting the bottle on the opposite 

 side and with the tap suitably turned, warming the bottle. When the fluid has been 

 forced up, or rather as it is being forced up, it may be necessary to break the bubble 

 by making the fluid meet the end of a pipe cleaner which has been pushed down as 

 far as it will go. 



In no case should one blow into the manometer. This will inevitably cause 

 a dampness that will make the oil form beads and prevent it rising and falling 

 accurately 



To calibrate the Differential Blood Gas apparatus*. 



The calibration consists in a determination of the relation between the quantity 

 of gas x evolved in the apparatus and the difference of pressure p, measured in the 

 manometer, x=kp. The method depends upon the liberation of a known quantity 

 of gas inside the apparatus ; x then is known and p is observed, therefore if k is the 

 constant of the apparatus it is directly determined 



*-*. 



P 



The reaction which has proved most serviceable so far has been the liberation of 

 oxygen from hydrogen peroxide in the presence of acid by the addition of potassium 

 permanganate. The equation is as follows : 



Therefore 316 grams of potassium permanganate yield five molecular weights or 

 111,000 c.c. of oxygen, at normal temperature and pressure. A solution of hydrogen 

 peroxide must be made up and freshly titrated with approximately decinormal 

 potassium permanganate, of such a strength that 1 c.c. of the H 2 2 gives off 0'2 c.c. 



* See also Hofmann's method, Journal of Physiol. XLVII. p. 272. 



