METHODS OF ANALYSIS FOR CERTIFIED COLORS. 



213 



dye with ammonium hydroxid containing one-tenth its volume of 

 ammonia (specific gravity 0.90). Dissolve the precipitate from the 

 paper with 1 : 1 nitric acid, the washings being collected in a large 

 porcelain crucible; add 5 cc of sulphuric acid to the contents of the 

 crucible, and evaporate the whole, almost to dryness. It is not nec- 

 essary that the solution should be colorless at this point, a brown 

 colored solution giving equally accurate results. Add 20 cc of water 

 to the residue in the crucible and then 10 cc of 

 a saturated solution of sulphur dioxid; evapo- 

 rate the solution to a sirupy consistency to 

 remove the sulphur dioxid, and then take up 

 in 20 cc of water and place in a 30-cc evolution 

 bottle, add 5 cc of concentrated sulphuric acid, 

 and determine the arsenic in the form of appa- 

 ratus (fig. 1) used by Bishop in his modification 

 of the Gutzeit test, the stains obtained being 

 compared with those given by known amounts 

 of arsenic. 



The apparatus used by Bishop consists of 

 the following parts: A 30-cc salt mouth evo-. 

 lution bottle into which is fitted a one-hole 

 rubber stopper carrying a glass tube 6.5 cm 

 long with an internal diameter of 1 cm, this 

 tube in turn being provided with a one-hole 

 rubber stopper fitted with another tube of the 

 same diameter and 5.5 cm long, the diameters 

 of both tubes being constricted at the points at 

 which they are inserted in the rubber stoppers. 

 A third glass tube 15 cm long, having an in- - 

 ternal diameter of 2.5 mm, is fitted into the 

 second at its upper end by means of a rubber 

 stopper. The first tube contains a strip of filter 

 paper which has been saturated with a 5 per 

 cent solution of lead acetate and dried. The 

 second tube contains a loosely packed plug of 

 cotton-wool freshly moistened with a 1 per cent FIG. i. Apparatus for the 



S01U tion Of lead acetate. Into the topmost tube determination of arsenic. 



is inserted the strip of sensitized paper to receive the arsenic stain. The 

 arsin is generated by introducing into the evolution bottle six pieces of 

 Kahlbaum's stick zinc (arsenic-free for forensic purposes) weighing 

 in all about 8 grams, and to assist in an active and constant evolution 

 of gas a disk of platinum is also placed in each bottle to form an elec- 

 trolytic couple. The evolution of gas is allowed to proceed for one 

 hour. The stains are produced on strips of hard pressed white paper 

 (2 mm wide and 120 mm long) that has been sensitized by being 



