8 U. S. COAST AND GEODETIC SURVEY 



into the volumetric flask, rinse out the beaker carefully with the wash 

 bottle, and pour the rinsing water into the volumetric flask. Rinse 

 down the inside of the neck of the flask with the wash bottle. Care- 

 fully fill the flask with distilled water up to the mark in the neck 

 so that the mark is just tangent to the bottom of the meniscus. 



If these instructions have been carried out with reasonable care, 

 the solution will be quite accurately of the required strength. The 

 rubber stopper and bulb may now be removed from the top of the 

 aspirator bottle and the silver-nitrate solution poured in, making 

 sure beforehand that both burette pinch cocks are closed. Replace 

 the rubber stopper and bulb into the aspirator bottle, pump up a lit- 

 tle air pressure, loosen the rubber stopper in the top of the burette, 

 and by means of the upper pinch cock fill the burette partly full of 

 solution. Place the beaker that is reserved for silver-nitrate solution 

 under the burette and allow solution to run into it until all parts of 

 the burette attachment, especially the glass tip, are full of solution, 

 with no air bubbles. 



Again remove the rubber stopper and bulb from the top of the 

 aspirator bottle, pour into the bottle the solution that has run down 

 into the beaker, and replace securely the rubber stopper and bulb in 

 the top of the bottle and the rubber stopper in the top of the burette. 



The purpose of the rubber stopper in the top of the burette is to 

 prevent evaporation. It must be loosened when the apparatus is in 

 use, but must be kept securely in place when the apparatus is not 

 in use. 



Silver-nitrate crystals undergo chemical change when exposed to unfiltered 

 sunlight, and it is for this reason that they are usually stored in amber-colored 

 glass bottles. This colored glass seems to protect them quite effectively from 

 the short, chemically active light waves. Care should be taken that the crystals 

 are not exposed to the light unnecessarily. 



Silver-nitrate solution apparently does not deteriorate seriously under the 

 action of light. J. W. Sale, of the Food, Drugs, and Insecticides Administration, 

 says that they keep their solution in a clear-glass bottle exposed to light and 

 that the solution appears to keep its strength indefinitely. He calls attention, 

 however, to the recommendation in the United States Pharmacopoeia that sil- 

 ver nitrate volumetric solution be kept in an amber-colored, glass-stopijered 

 bottle. An article by A. H. Clark, in the Journal of the American Pharmaceuti- 

 cal Association, volume 1, 1912, page 228, states that a tenth-normal solution 

 of silver nitrate was standardized in December, 1909, and when restandardized 

 two years and eight months later was found to have the same concentration 

 lo the fifth significant figure. The solution apparently had been kept in an 

 amber-colored, glass-stoppered bottle during the interval. It is considered quite 

 safe, however, to keep the solution in a clear-glass aspirator bottle, especially 

 since it will be exposed to light only when the apparatus is in use and the 

 locker is open. 



It must be admitted that the use of rubber connections in the apparatus is 

 not desirable. Several chemists have stated, however, that trouble from this 

 source is not likely if the glass tubes are placed close together at the rubber 



