4 Mr Barcroft, Apparatus for the 



In order to reduce the strain on the pump, due to the weight 

 or disposition of the rest of the apparatus, two permanent rubber 

 joints have been introduced. These are marked (a) and (b) on 

 Fig. 1 ; (a) is shewn in detail. The glass ends are joined with 

 stout pressure tubing, smeared inside and out with Canada 

 balsam. The tubing is bound on with ' grips '. These ' grips ' I 

 had made to obviate the risk of breaking the pump, which occurs 

 in the binding on of wire. One of them is shewn incidentally in 

 Fig. 2. 



. For drying the gases I have used a tower about eighteen inches 

 in height, containing pumice wet with sulphuric acid. The sul- 

 phuric acid can readily be renewed when spent, being poured in 

 at k. In the lower part of the tower some sulphuric acid is 

 allowed to lie, at once helping the drying process and rendering 

 obvious any leak in the tap (h). 



If, as is necessary, more than four or five samples of blood 

 are to be analysed successively, the entire acid in the drying 

 chamber must be replaced without introducing air; the apparatus 

 may be set up as figured in Fig. 1. The vessel r contains 

 mercury, and is so placed that with a vacuum in the pump the 

 mercury rises to about the level x. The sulphuric acid is put 

 in at the top of the tower and flows over the pumice. Sufficient 

 is put in to fill the bulb g to the level of the tube q. Much of 

 the aqueous vapour from the gases coming along m condenses on 

 the surface of the sulphuric acid, forming a film of dilute acid. 

 By raising the vessel r and opening the tap connecting g with 

 the vacuous chamber, p, this dilute acid can be disposed of. 

 Similarly, if fresh acid be put in at the top of the tower, the 

 excess can be put into p, otherwise m would become closed up. 



The Receiver. 



This part of the apparatus divides itself into that for measuring 

 the blood, and that for exposing it to a vacuum ; both of which 

 appear illustrated in the Figs. 2 — 8. Fig. 2 refers to the measur- 

 ing burette. This burette consists simply of a vertical graduated 

 tube B of about 11 c.c. capacity connected at its lower end by 

 means of pressure tubing with a small mercury reservoir, J. At 

 its upper end the graduated tube, B, terminates in a glass tap, A, 

 of peculiar construction. The stopper is shewn in detail in Fig. 3. 

 Leading to the tap are two horizontal tubes, G and D. Of these C 

 is connected with the cannula from which the blood is to be drawn, 

 whilst D is joined at the point / to the froth bulbs shewn in 

 Fig. 4. From Fig. 3 it will be obvious that the passage F may 

 be continuous with either G or D, or with neither of these, 



