and Laboratory Methods. 



1919 



the standards at X bearing figures denoting the amount of nitrogen or ammo- 

 nia in the adjacent standard. If these are placed in reverse order they will 

 appear in the mirror m" right side up. Owing to the flood of light through 

 the slot S it is advantageous to place a blinder (consisting of a board 2x6 in., 

 with one hole for the tube) over the end of the tube. The whole cabinet should 

 be painted a dull black. The dimensions to fit our tubes {Y^xly^ in.) are given 

 with the figure. 



DISAGREEABLE PIPETTING MADE EASY. 



The simple device here described has been found of great value where it is 

 necessary to pipette off large quantities of water for chemical examination, 

 especially waters heavily polluted by sewage. The analyst is not only always in 

 danger of sucking up a mouthful of the infectious, malodorous water, but, as is 

 well known, the process becomes a very tiresome one when it is often repeated. 



The apparatus constructed and in use in this laboratory consists of a large 

 heavy glass bottle A, of about four liters capacity, fitted with a two-hole rubber 

 stopper B clamped very firmly 

 to the neck of the bottle by 

 wire or otherwise, through 

 which pass two glass elbows 

 C,C'. To each elbow is at- 

 tached a piece of rubber tubing 

 P, P'. This is best held in 

 place by wiring. Each piece 

 of tubing is provided with a 

 pinchcock D, D'. The piece 

 of apparatus is now complete. 

 The bottle with its fittings is 

 next connected with the tap of 

 the city water supply by means 

 of rubber and glass tubing. 

 The pinchcock D remains 

 closed, while D' is opened at 

 the same moment that the 

 water from the tap is turned on 

 in the bottle 



Apparatus for filling Pipettes in Water Analysis. 



The water rushes in and compresses the air 

 As soon as the bottle is one-third full of water the pinchcock D' is 

 closed and the tap turned off at the same time. You now have a bottle two- 

 thirds full of compressed air, obtained in a very easy way. The bottle is now 

 taken to where the pipetting is to be done. 



In our work the water to be examined is contained in 250 c. c. Erlenmeyer 

 flasks, those with wide necks being preferred. A two-hole rubber stopper I, 

 through which pass the pipette S, of desired capacity, and a small glass elbow R, 

 is next fitted to the flasks. By carefully selecting flasks with uniform sized necks, 

 one stopper will be sufficient. The glass elbow R is now connected with the 

 bottle of compressed air by rubber and glass tubing Z, O. Next the stopper I is 

 inserted into the neck of the Erlenmeyer flask, the jet of the pipette below the 

 surface of the water, and the whole is held in place by the left hand. The 

 pinchcock D is now opened very gently with the right hand and the air rushes 

 into the flask M, forcing the water up into the pipette. 



By a little practice one is able to regulate the amount of air necessary to fill 

 the pipette. With the apparatus here described we have been able with a single 

 charging to pipette off a liter of water. When the air is exhausted from the 

 bottle, more water is run in and a new supply of compressed air obtained. 

 University of Chicago. F. L. STEVENS AND W. G. SaCKETT. 



