The Estimation of Acidity. 



255 



The Operation of the Electrode. 



As has previously been remarked, in this laboratory, the simple 

 •electrode devised by Barendrecht has been used to the exclusion 

 of all others in routine work. In Barendrecht's original article 

 it will be seen that the fluid is drawn up and down the glass 

 vessel by a close fitting syringe. This is shown in Fig. 10. To 



Fig. 10. 



After Barendrecht 



.do this by hand in the usual way made it difficult at times to 

 .affect the fine adjustment needed to obtain a minimum con- 

 tact. The writer has therefore devised a ratchet and pinion at- 

 tachment, which is connected to the plunger of the syringe, 

 which allows a very exact adjustment to be made with but little 

 trouble. 



A diagramatic view of the device is shown in fig. 11, where 

 a is the " syringe," and b the perforated plunger, which is con- 

 trolled through the rackwork by means of the milled wheel g. 

 The hydrogen is admitted at c, and the glass electrode tube e 

 is attached closely to the apparatus by a rubber tube d. The whole 

 arrangement is made adjustable on the stand /. 



The technique of using this apparatus is as follows: — Having 

 thoroughly ventilated the electrode with hydrogen, and before 

 the fluid to be investigated has been drawn up the tube, the 

 plunger should be moved in and out by means of the milled 

 wheel in order to remove any trace of air which might be oc- 

 cluded between it and the end of the tube; then, with the hy- 

 drogen passing through the electrode slowly, the open end of 

 the glass tube is brought below the surface of the liquid to be 



