BAIRD &TATLOCK (LONDON) LTD. 



788 



789 



88 T Barcroft's Apparatus for the differential Pressure of Blood Gases, No. 1, devised l>v 

 Joseph Barcroft, F.R.S., and H. Roberts. Price complete, as figured . . each 



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DESCRIPTION. 



The Apparatus consists of two bottles of identical size (about 30 cc.) attached to a manometer, the tubing 

 which is i mm. bore. The manometer is filled with clove oil of known specific gravity. To fill it take out 

 e centre tube, put in clove oil at (A), put in the centre tube with the glass tube (u) open and apply some pressure 

 i the rubber tube (c). The oil should stand about half way up each tube ; seal (B) in a llanie. 



The following constants must be determined : (i) the sectional area of the tubing. A ; (2) the size of the 

 tiles, V. 



To determine A : The centre tube (x) is marked in i/iooths of a cc. Expel o. i cc. from it into the mano- 

 cter tubes, which are of the same size. 0.05 cc. will have gone into each ; read the difference in level. From 

 e mean of a number of such readings (D) is directly deducible. 



To determine V : With a knowledge of (D), V may be obtained by an application of Boyle's Law. Fill 



bottles almost full of water, putting say 25 cc. of water in each, shut one of the taps, keeping the other 

 H'ii. lighten the screw so as to produce a known compression on the closed side ; observe the difference of 

 essure produced. The tubes should be moistened with oil before the experiment commences. 



To determine the oxygen capacity of a sample of blood .'Place 2 cc. of Ammonia solution (made by adding 

 cc. of strong NH 3 t6'a'litre of water) ; add i cc. of blood on each side. Thoroughly lake the blood. Put vaseline 

 i the large and small stoppers, place the bottles on the stoppers. Put . 2 cc. of a saturated solution of Potassium 

 rricyanidc in the small tubes contained in the stoppers (this is best done with a fine pipette which goes down 

 noes). Put in the small stoppers. Place the apparatus on the side of a large water bath (such as a 

 lil). In about five minutes, with both taps shut, rotate one bottle till the Ferricyanide trickles into the laked 

 ood. Shake thoroughly, replace in the bath, repeat this several times till a constant difference of level i-; 

 >tained. Let this difference of level by y mm. ; let p be the height of the barometer in mm. of clove oil. an I 

 the volume of oxygen given off in c.mm. x = y ( - + A I. Except in the most exact work p may be taken 



10,000 mm., in which case the expression (- + 0.785 d* j may be determined once for all and called C ; the 

 nstant of the apparatus then x y + C. See Journal of Physiology, XLIL, p. 512. 



Barcroft's Differential Apparatus, No. 2, for the Analysis of o.i cc. of blood. 



Price complete with clip, as figured 



each 



For the systematic determination of the haemoglobin worth or dissociation curves of human beings. For 

 iolute values it is best to determine the constant of the apparatus by comparison with the larger apparatus ; 

 same blood being used for both. 



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