52 THE QUANTITATIVE SYNTHESIS OF ARGENTIC NITRATE, ETC. 



in the nephelometer. Occasionally, some was found, but the corrections 

 required were not large. Nevertheless, the possibility that the fused 

 nitrate had attacked the glass was always disturbing, and the inconven- 

 ience and uncertainty of this correction made its elimination desirable. 

 Accordingly, in the final determinations, a section of quartz tubing, Q, 

 3 mm. in diameter and 15 mm. long, was firmly attached to a platinum 

 wire and lowered till it barely projected into the body of the flask. This 

 supporting wire hooked into the collar, so that the quartz tube could be 

 removed while the silver was dissolving. During the evaporation, how- 

 ever, it was in place, and the end of the glass delivery tube was shortened 

 and drawn down to fit into it. The glass tube was still tested as before, 

 but no silver was ever recovered from it. Hence the flask and the quartz 

 tube must have retained all the silver originally weighed out. 



The evaporation of the liquid was easily and quickly conducted in this 

 apparatus. If the flask was not more than half full and the air passed 

 through the drying train no faster than two bubbles per second, it was 

 possible to maintain the temperature of the oven at 125 without risk of 

 ebullition. The vapors drawn out as before described passed first through 

 a U-tube filled with moist glass beads and just sealed with water, after- 

 wards through a tower of caustic alkali to take out nitric acid which might 

 attack the water-pump. When the liquid became coated with a film of 

 crystals the temperature was lowered to 110; bubbles of vapor now 

 formed gradually under the crystal layer, and the slight spattering caused 

 by their rupture could be seen on the inside walls of the flask. The oven 

 was now suddenly cooled, so that the vapors from the hot liquid, condens- 

 ing on the walls of the flask, washed down the crust which had formed 

 during evaporation. Upon continuing the heating, a porous crust was 

 soon formed, under which the formation of steam caused no spattering. 

 Finally, the temperature was raised gradually while the last trace of 

 liquid was disappearing. The solid was dried for a quarter of an hour 

 at 150 in the dark, and then heated to 230 01 to insure complete fusion, 

 not only of the main portion, but also of any portions projected on the 

 upper walls of the flask. The temperature was soon lowered to 210, 

 which sufficed to keep the mass in fusion, and the air current was con- 

 tinued for an hour. Then, in subdued light, the flask was lifted out 

 by a loop of platinum wire passed through its collar, placed on a net- 

 work of platinum wire, and tilted in all directions to cause the nitrate to 

 solidify in a thin layer on the walls. Once this precaution was neglected 

 and the flask was cracked by the contraction of the nitrate on cooling. 



1 This temperature and the others to be recorded later have not been corrected for 

 the exposed steam. They do not indicate the exact meeting-point of the salt. 



