- OP THE AMERICAS A< ADEHT. 



On ' ' ■ - b change to a faint gray, becoming darker 



Further standi] 



r with amnionic hydroxide suggi ■ -once of 



but it ifl Dot clear whether a decomposition into 



mei chloride takes place before the Mack color is formed. If 



red band is treated with hydrochloric acid, washed, and then 



]. lared in ammonic hydroxide, the color is not an intense black, but 



rather graj ish in tune. 



imi of interest is that with auric chloride. If the 



1. after treatment with hydrochloric acid, is placed in a small test 



tube with a few drops of hundredth normal auric chloride and allowed 



'and for live or ten minutes, a beautiful purple color results. The 



ction is characteristic for larger amounts of arsenic. 



The reacti : the formation, development, and decomposition of 



the col are susceptible of various interpretations, but, as we 



id bef re, a quantitative stud)- is necessary before exp] 

 an opinion, not only as to the formula of the red body and the mech- 

 lii of its formation and decomposition, but also on the existence 

 of intermediate yellow compounds or their formulae. 



Bird M has applied Bettendorffs reaction to the stains, substantially 

 as follows: Tin 1 disk of paper containing the color is extracted with 



• . r two cubic centimeters of warm, concentrated hydrochloric acid. 

 The extract is oxidized hy a few drops of bromine in hydrochloric acid 



1 in a small test tube with an equal volume of ."<> per cent 

 inous chloride. On warming, the pinkish brown color appears. 



Interference of the Hydrides of Sulphur, Phosphorus, 



and Antimony. 



There is considerable confusion in the statements of various authors 



• i the color -tains from these gases on mercuric chloride paper, and 



! ird's mi re careful study is open to the common criticism that 

 the descriptions are not given with reference to known amounts of the 

 hydrides. In determining to what extent these substances interfere 

 in our method, we have at first ascertained by trial how much of the 



ticular hydride will give a comparable band on the mercuric chlo- 

 ride paperunder the same conditions, — particularly in the same time. 

 \\ .• then studied (he effect of a given treatment upon each color band, 



i afterward compared the effect of each reagent upon the four ap- 

 proximately equivalent bands. 



26 Loc. cit 



