68 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



salt had been fused, a current of dry nitrogen was passed into the com- 

 bustion tube and the hydrochloric acid generator was disconnected. The 

 nitrogen was prepared by passing mixed air and ammonia over rolls of 



copper gauze heated to redness, the excess of 

 ammonia being removed by passing the gases 

 through wash bottles containing dilute sulphuric 

 acid ; and the nitrogen was dried in a set of 

 towers similar to those used for drying the cur- 

 rent of air. AVlien the tube was cool, the cur- 

 rent of dry air was turned on, and the tube and 

 its contents washed out as in previous experi- 

 ments. 



As there were no especial objections against 

 the use of rubber connections and stoppers in 

 the part of the apparatus used for drying the 

 air, several large towers were employed, each 

 filled with crushed pumice stone and saturated 

 with sulphuric acid previous to using. Both air 

 and nitrogen were finally dried by resublimed 

 4/ ^Ipw I phosphoric pentoxide. The bottling and com- 



'"' vv*<y// lIU bustion tubes were of the same construction as 



in the former apparatus, except that they were 

 larger. 



In the second series, the method of icrnitinof 

 the double salt to obtain the magiiesic chloride 

 was the same as in the first ; but the method 

 of estimating the amount of chlorine present was 

 different. From the approximate atomic weight 

 of magnesium already found, a calculation was 

 made as to the amount of silver necessary ex- 

 actly to precipitate the chlorine present in the 

 sample of magnesic chloride taken. This amount 

 of silver was weighed out as nearly as possible, dissolved in nitric acid in 

 an Erlenmeyer flask, provided with a set of bulbs to catch the spray from 

 the evolution of gas, and added to the solution of magnesic chloride con- 

 tained in a large flask. The flask was thoroughly agitated in the dark, 

 and allowed to stand over night. Fifty cubic centimeters were then 

 withdrawn by means of a pipette, and tested by means of a nephelometer, 

 or apparatus for determining the amount of precipitate from the intensity 

 of the opalescence produced by it. This piece of apparatus was cod- 



FiG. 3. — One of the Towers 



USED FOR BRYING IlTDnO- 



CHLORic Acid. 

 Seventy centimeters high. 



