URINE 



449 



which is drawn to a fine bore and bent up almost at a right angle. All joints must 

 be air-tight. 



Introduce 30 to 40 grams of arsenic-free granulated zinc into the flask, insert 

 the stopper and through the funnel introduce 50 c.c. dilute sulphuric acid (i part 

 to 4 parts water). After a few minutes collect a test-tube of gas by inverting a 

 test-tube over the end of the quartz tube, and test it by igniting. When the gas in 

 the test-tube ignites quietly, light the gas issuing from the quartz tube. 



Hold a clean porcelain crucible lid in the flame and note whether any deposit 

 occurs. This precaution must be taken to insure that the chemicals and apparatus 

 are not contaminated with arsenic. 



Now introduce the prepared urine solution into the funnel and adjust the flow 

 so that 6 to 8 drops are introduced into the flask per minute. Immediately hold a 

 clean porcelain crucible lid in the flame and at the first evidence of a dark deposit 

 apply heat, using a wing-top burner, to the quartz tube. The arsenic if present 

 will deposit in the quartz tube beyond the flame. Now test the spot on the lid 

 to see if it is arsenic; it should dissolve readily in sodium hypochlorite solution. 



FIG. 131. MARSH APPARATUS. 



Continue the operation for two hours, remove the Bunsen burner and again hold 

 the lid in the flame. If no more deposits on the lid, the arsenic has all come over 

 and is deposited in the quartz tube; if deposition occurs, apply the Bunsen again 

 and repeat. 



When complete, remove the quartz tube, weigh it after cooling, then dissolve 

 out the arsenic with nitric acid, wash, dry, and weigh again. The difference in 

 weight is the weight of metallic arsenic in the volume of urine taken. 



2. Reinsch's Test. This test is very much simpler, but not so delicate. It 

 has the advantage of application in the presence of organic matter. The test is 

 performed as follows: The urine, acidified with one-fifth its volume of pure hydro- 

 chloric acid, is placed in a beaker. A piece of bright copper foil free from arsenic 

 is then introduced, and the urine heated almost to the boiling-point. It is then 

 set aside for six to eight hours. The arsenic is deposited on the copper foil, bluish- 

 gray color. The foil is then removed, washed successively in pure water, alcohol, 

 ether, and dried without heat. The foil is then, rolled into a scroll and inserted 

 into a 3 mm. bore glass tube 4 inches long, about i inch from the end. The tube is 

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