200 MERCURIAL PUMPS. [BOOK I. 



Alexander Schmidt 1 . It consists in reality of a combination of 

 two mercurial pumps. The vessel containing the blood of which 

 the gases are to be determined, G, is connected with the bulb B. 

 When a complete vacuum has been made in B arid in C, the stop- 

 cock E is closed, is opened and G is plunged into hot water. 

 The blood enters into ebullition and its gases pass into B, some 

 of the blood also passing into that vessel. By opening E and K, 

 the gases are collected in (7, and K being then turned so as to shut 

 C off from B but to place it in communication with D, the latter is 

 raised so as to compress the gas in C\ on now opening the stop- 

 cock F, the gas maybe made to pass through H into a gas jar standing 

 over mercury. This very brief description will be understood by 

 carefully examining the drawing, especially if the reader make him- 

 self acquainted with the construction of Pfliiger's or Alvergniat's 

 pumps as described in the succeeding paragraphs. 



In using Ludwig's pump, the blood is always defibrinated before 

 analysis. The blood to be analysed is introduced, without coming in 

 contact with air, into the receptacle G, which has previously been 

 filled with mercury and detached from the pump. The bulb having 

 a known capacity the volume of the blood analysed is known. 



Pfluger's The pump, of which one form is represented by 



pump. y-g 4^ possesses arrangements whereby watery vapour 



which is disengaged in vacuo is at once absorbed. 



G, C, E, F, D, represent parts of the pump proper ; C is the barometric 

 chamber of about two litres capacity, provided at G with a three-way 

 cock, which enables the chamber to be shut off or placed in communication 

 either with the chambers to be exhausted, B, A, or with the open 

 air, or by means of the glass gas delivery tube H with a mercurial 

 pneumatic trough. D is a bulb larger than C, and communicating with it 

 by means of a stout caoutchouc tube covered externally with a stout woven 

 fabric, so as to enable it to resist considerable internal pressure without 

 dilating. D is contained in a box which may easily be wound up and 

 down by means of the ratchet-wheel L, and the band and pulley connected 

 with it. 



Mercury is poured into the filling globe />, when the latter is in its 

 lowest position. By winding D up until its level is above that of C, 

 and placing the stop-cock G in such a position that C communicates with 

 the external air, the bulb C is filled with mercury. The stop-cock G is 

 then turned so as to shut off C completely from communication above. 

 On now bringing D down to its initial position, viz., about a metre 

 below (7, the mercury in the latter sinks until it stands at the height 

 of the barometer above the mercury in the reservoir D. There is then 

 a Torricellian vacuum in C. By a suitable turn of the three-way cock G, 

 the chamber C is now brought into communication with the apparatus 

 to be exhausted. After the gas contained in the latter has diffused 



1 Alex. Schmidt, " Ueber die Kohlensaure in den Blutkorperchen." Erste Abhand- 

 lung. Ber. d. Tconigl. sachs. Gesellsch. d. Wissenschaft. zu Leipzig. Math.-phys. Classe. 

 Vol. xix. (1867) S. 33. 



