■ r Till: AMERICAS ACADEMY. 



11 these results it will be .seen that if we have a color band from 

 pure material, within or above the range of the l mm. arsenic stand- 

 ards, the differentiation of i from antimony, phosphorus, and 

 r [a pei imple. With Bmallei amounts, or especially with 

 lm ., •here can be no confusion with antimony, Bince siiljine 

 m color on the paper. With sulphur, while the small 

 initial band might be mistaken for arsenic, the treatment with hot 

 ammonia, and auric chloride will easily identify it. But with 

 phosphorus there is likely to be a doubt it' the 2 mm. hand 20 is very 

 ,!, since the amount and Length of the color do not permit the 

 . - in the larger bands. A i we have shown, however, 

 that even as much as o. 1 mg. of phosphorus gives very little color in 

 thirty minutes of reduction, and as this is a quantity which can be easily 

 oxidized in the preparation of the solution for analysis, we should have 

 little to fear from smaller amounts than 0.1 mg. Such amounts might 

 considered quite accidental. 



of Hydrogen Sulphide, Phospkine, or Stibine <>>i the Arsenic 



/. Very different is it, however, when the arsenic .solution also 



gives by reduction as much of any one of these gases as would alone 



yidd a band equal to the arsenic band in length. This is shown by the 



following experiments. 



Hydrogen Sulphide. Amounts of the respective solutions, equal to 



30 mmg. of arsenious oxide and ."><> mmg. of sulphur, were added to- 



toa bottle and reduced for thirty minutes. Instead of the short, 



well-defined band of the arsenic, a band Dearly three quarters of the 



length of the strip was formed, of a reddish yellow color. Hydrochlo- 



I turned it slightly redder, but the appearance was not definitely 



characteristic of arsenic. On another similar band ammonia brought 



splotches of black on a red ground. The arsenic had evidently 



ielerator in the reduction of the sulphurous acid, and the 



1 was due to a mixture of the arsenic and sulphur coui- 



I ■•< : a greater surface. 



Phosphine. Solutions containing 30 mmg. arsenious oxide and 



phosphorus were added to a bottle and reduced for thirty 



miii. The band was longer than the corresponding band of ar- 



with the characteristic appearance of the latter, — well 



• that it was Bomewhat lighter at the top. Hydrochloric 



1 the color to the well-marked red of arsenic and the 



with the hydrochloric acid standard for 30 mmg. Auric 



29 For tin.' u*c of tlic - mm. banc], see below. 



