RICHARDS. — MODIFICATIONS OF HEMPEL's GAS-APPARATUS. 275 



vided with a levelling bulb or funnel, answers very well as a measuring 

 instrument. The burette may even be used in its usual position, if it is 

 provided above with a smooth rubber stopper with a single hole for the 

 capillary connecting-tube. Of course the stopper is always pushed pre- 

 cisely into a definite position, indicated by a carefully made mark on the 

 burette. There is little risk of displacing this stopper if it is firmly wired 

 into place. In any case of course the ungraduated space at the upper 

 extremity must be carefully calibrated. Au especially made 50 c. c. in- 

 strument, graduated all the way to the capillary tube at the top, is more 

 convenient, although no more accurate than the inverted burette. For 

 convenience in cleaning, it is well not to have both ends of the burette 

 drawn down to small diameter. The small size of the burette makes it 

 easily possible to provide the water jacket which is so essential for accu- 

 rate work, and both burette and pipette may be supported upon the ordi- 

 nary iron ring stand. 



III. Practical Operation. 



Of course the precautions usually necessary in gas analysis must be 

 used in all the operations with this apparatus. For example, due time 

 must be allowed for the running dowu 

 of the liquid from the moistened walls. 

 Again, care must be taken that the same Hvf 



amount of gas, at definite pressure (as 

 small an amount as possible) is always 

 left in the connecting capillary tubes. 

 In order to make sure that no air- 

 bubbles are caught, it is well to draw 

 out the ends of the tubes in the manner 

 illustrated in the diagram, which indi- 

 cates two successive stages of the glass 

 blowing, as well as the finished and con- 

 nected nipple. The object of blowing 

 the small bulbs is to render the bore of 

 the portions drawn out as large as that 

 of the rest of the tube. 



While the apparatus thus constituted 

 was devised primarily for use in an emer- 

 gency, it has several advantages over Figure 2. 

 the Hempel apparatus. It dispenses 

 with the necessity of calibrating the whole length of a new burette, it 



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