312 PROCEEDINGS OF THE AMERICAN ACADEMY. 



On the next day there was a change to a faint gray, becoming darker 

 on further standing. 



The black color with amnionic hydroxide suggests the presence of 

 mercurous chloride, but it is not clear whether a decomposition into 

 mercurous chloride takes place before the black color is formed. If 

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

 placed in ammonic hydroxide, the color is not an intense black, but 

 rather grayish in tone. 



Another reaction of interest is that with auric chloride. If the 

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

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

 to stand for five or ten minutes, a beautiful purple color results. The 

 reaction is characteristic for larger amounts of arsenic. 



The reaction of the formation, development, and decomposition of 

 the color bands are susceptible of various interpretations, but, as we 

 have said before, a quantitative study is necessary before expressing 

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

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

 of intermediate yellow compounds or their formulae. 



Bird 26 tas applied Bettendorff's reaction to the stains, substantially 

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

 one or two cubic centimeters of warm, concentrated hydrochloric acid. 

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

 and treated in a small test tube with an equal volume of 30 per cent 

 stannous 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 

 as to the color stains from these gases on mercuric chloride paper, and 

 even Bird's more 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 

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

 ride paper under the same conditions, — particularly in the same time. 

 We then studied the effect of a given treatment upon each color band, 

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

 proximately equivalent bands. 



25 Loc. cit. 



