AUTOMATIC PIPETTES 13 



conveniently sterilized in ordinary metal thermometer 

 cases (Fig. 16). 



Graduated Capillary Pipettes (Fig. 17). These should 

 also be made in the laboratory from manometer 

 tubing- of simple, convenient shape, and graduated 

 by the aid of "standard" pipettes (in hundredths) to 

 contain such quantities as 10, 50, and 

 90 c.mm., and carefully marked with a 

 writing diamond. These, previously 

 sterilised in large test-tubes, will be 

 found extremely useful in preparing 

 accurate percentage solutions, when 

 only minute quantities of fluid are 

 available. 



Automatic ("Throttle") Pipettes. 

 These ingenious pipettes, introduced 

 by Wright, can easily be calibrated 

 in the laboratory and are exceedingly 

 useful for graduating small pipettes, p IG< 17. capii- 

 f or measuring small quantities of fluids, ! a r y graduated 



. & A ,. H , ' pipettes. 



in prepanng dilutions of serum for 

 agglutination reactions, etc. They are usually made 

 from the Capillary Pasteur pipettes (Fig. 13, a). The 

 following description of the manufacture of a 5 c.mm. 

 pipette will serve to show how the small automatic 

 pipettes are calibrated. 



1. Select a pipette the capillary portion of which is 

 fairly roomy in bore and possesses regular even walls, 

 and remove the cotton- wool plug from the open end. 



2. Heat the capillary portion near the free extremity 

 in the by-pass flame of the bunsen burner and draw it 

 out into a very fine hair-like tube and break this 

 across. This hair-like extremity will permit the pas- 

 sage of air but is too fine for metallic mercury to pass. 



3. From a standard graduated pipette deliver 

 5 c.mm. clean mercury into the upper wide portion of 

 the pipette. 



