70 METHODS OF ANALYSIS [Chap. 



CARBON DIOXID."— OFFICIAL. 



37 APPARATUS. 



This consists of a 200 cc. Erlenmeyer flask closed with a 2-holed stopper; one of 

 these holes is fitted with a dropping funnel the stem of which extends almost to the 

 bottom of the flask; the outlet of a condenser, which is inclined upward at an angle 

 of 30° from the horizontal, passes downward through the other hole. The upper 

 end of the condenser is connected with a calcium chlorid tube which in turn ia 

 connected with a double U-tube filled in the middle with pumice fragments, pre- 

 viously saturated with copper sulphate solution and subsequently dehydrated, 

 and with calcium chlorid at either end. Then follow 2 weighed U-tubes for absorb- 

 ing the carbon dioxid, the first filled with porous soda-lime, and the second, one 

 third with soda-lime and two thirds with calcium chlorid, the latter reagent being 

 placed at the exit end of the train. A Geissler bulb, partly filled with sulphuric 

 acid, is attached to the last U-tube to show the rate of gas flow. An aspirator is 

 connected with the Geissler bulb to draw air through the apparatus. An absorp- 

 tion tower filled with soda-lime is connected with the mouth of the dropping funnel 

 to remove carbon dioxid from the air entering the apparatus. 



38 DETERMINATION. 



Weigh 2 grams of the powder or 10 grams of the paste into the Erlenmeyer flask, 

 add about 20 cc. of water, attach the flask to the apparatus omitting the 2 weighed 

 U-tubes, and draw carbon dioxid-free air through the apparatus until the original 

 air is displaced. Then attach the weighed U-tubes in the position as described in 37, 

 close the stop-cock of the dropping funnel, fill half full with dilute hydrochloric 

 acid (1 to 1), reconnect with the soda-lime tower, and allow the acid to flow into 

 the Erlenmeyer flask, slowly if there is much carbon dioxid, rapidly if there is 

 little. When effervescence diminishes, place a low Bunsen flame under the flask and 

 start a flow of water through the condenser, a slow current of air being allowed to 

 flow through the apparatus at the same time. Maintain a steady but quiet ebulli- 

 tion, and a slow air current through the apparatus. Boil for a few minutes after 

 the water has begun to condense in the condenser, then remove the flame and con- 

 tinue the aspiration of air at the rate of about 2 bubbles per second until the 

 apparatus is cool. Disconnect the tared absorption tubes, cool in the balance case 

 and weigh. The increase in weight is due to carbon dioxid. 



COPPER. 



39 Electrolytic Method.— Official. 



Dissolve 2 grams of the dry powdered sample in 20 cc. of water and 5 cc. of con- 

 centrated nitric acid, dilute to 100 cc, wash into a weighed 150 cc. platinum dish, 

 and electrolyze, using a rotating spiral anode and a current of about 3 amperes. 

 After all the copper is deposited (.requiring about 30 minutes), wash the deposit 

 with water by siphoning, then rinse with alcohol, dry for a few minutes in an oven, 

 and weigh. Calculate the per cent of copper in the sample. 



40 Thiosulphate Method.— Official. 



Dissolve 2 grams of the dry powdered sample in about 50 cc. of 10% nitric acid, 

 add ammonium hydroxid solution in excess and heat; then, without removing the 

 precipitate which is formed, boil off the excess of ammonia, add 5-10 cc. of acetic 

 acid, cool, add 10 cc. of 30% potassium iodid solution, and titrate as directed under 

 VIIL 29. 



