90 Colorado College Studies. 



ate it, and to tint it slightly with iodine before pouring it into 

 the burette. 



The method of procedure is obvious. I will merely add that 

 in altering the position of the CSo index, it is well to let it rise 

 a little higher in the burette than the required graduation, and 

 then lower it by careful manipulation of the stop-cock n. The 

 burette should, of course, be kept stoppered as much as possi- 

 ble during the calibration. 



I would also particularly emphasize the fact that the method 

 works satisfactorily only when the calibration is effected as 

 described — from below, upwards. 



The readings obtained can be used for calibration as 

 described in detail in Bunsen's " Gasometry." 



In order to avoid errors of parallax in reading off the levels 

 of the CS., column, I silver a strip on the back of the burette 

 This mirror strip, which does away with all floats and similar 

 devices for avoiding errors of parallax in the subsequent use of 

 the burette, is easily made as follows. The burette having been 

 ^^ thoroughly cleaned externally, is corked air- 

 .. tight, and then inverted in a tall cylinder con- 



'^ \ s*,.,^ taining an alkaline silvering fluid* After 

 some time it is withdrawn and allowed to 

 become ihoroughhj air-dried. The silver can 

 then be easily removed from the front and 

 ■sides by scraping, followed by a final rubbing with a rag moist- 

 ened with dilute nitric acid. The slip of silver backing the 

 burette is then fixed by one or two coats of varnish. 



In reading such a burette it will be found advantageous to 

 look at the meniscus through a slit cut in a sheet of white 

 glazed paper, held at an angle to the vertical as shown in Fig. 

 ■% The burette graduations are also rendered very much more 

 distinct by rubbing the front of the burette first with a piece of 

 flannel on which a paste of turpentine and mercuric iodide has 

 been placed, and then with a dr y cloth. 



♦Suitable fluids are described in Roscoe & Scliorlemuier's Treatise on Chemistry 

 Vol. II., part I., p. 303. 



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