MoLLETX. — On a new Form of Burette. 693 



cork, through which plays a glass rod, reaching down to the bottom and 

 ground conically, so as to fit watertight into the tapering delivery-end of the 

 burette. A lateral aperture at the top serves to charge the instrument. 

 This form is useful in working with solutions of permanganate of potash or 

 other reagents which attack the indiarubber which in Mohr's pattern con- 

 nects the delivery-tube to the body of the burette." (PL XXXVII., left- 

 hand figure). 



This pattern, owmg to the central rod, does not admit of the insertion 

 of an Erdmaun's float. If the glass rod is broken it is next to impossible 

 to obtain one exactly similar in gauge, and unless such an one is obtained 

 the burette is useless, the graduations having been made when the original 

 rod was in the tube. This is a serious objection which cannot be overlooked. 



The burette which I now purpose to describe is readily cleansed, may 

 be used with potassium permanganate, and allows of Erdmann's float being 

 employed. This burette consists of a graduated tube, drawn out at the 

 lower extremity to a moderately small aperture. The top of the tube is 

 closed by a cork fitting airtight, through which passes a small glass tube. 

 This tube, an inch or two above the cork, is bent at right angles into a 

 horizontal direction and then again vertically but downwards. A short 

 piece of caoutchouc tubing is slipped over the end of the small tube, which 

 terminates a few inches above the delivery aperture of the larger one. A 

 screw clamp fastened on to the burette-stand serves to pinch the caoutchouc 

 tubing, and by varying, as required, the pressure on the latter the flow of 

 liquid is regulated, or arrested entirely. By inserting a short length of glass 

 tube into the free end of the caoutchouc (the pressure on which has been 

 released for the time being) and applying suction the burette may be filled 

 with ease, in a very short time, and without the production of a single 

 bubble (pi. XXXVII., right hand fig.). 



This form cannot be used in cases where the solution is required to 

 stand for two or three days in the burette, to be used for a fresh analysis, 

 as the air confined above the liquid is subject to the variations of tempera- 

 ture, which when rising would cause the solution to be slowly forced out of 

 the delivery aperture. 



It may not be out of place to remark that Mohr's burettes, the stopcocks 

 of which have been broken off, may easily be converted into the new form 

 and thus be rendered serviceable again. 



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