Langenhan—The Arsenical Solutions. 
181 
The third paragraph is a test for the absence or presence of 
arsenate. In the presence of hydrochloric acid the precipitate of 
silver arsenate does not form due to its solubility in the acid solu¬ 
tion. If to the acidulated solution then, some Silver nitrate T. S. 
is added and a layer of ammonia water superimposed upon it a 
reddish brown color at the line of contact indicates the presence of 
silver arsenate. The reaction has been expressed in the following 
manner : 105 
/OK /-OAg- 
0= As —OK + 3 AgN0 3 =B 3KN0 3 + 0= As —OAg 
\OK \OAg 
Supplement to Tests. According to the U. S. P. “An aqueous 
solution of Arsenic Trioxide is faintly acid to litmus. ’ ’ Whether 
this same acidity is shown towards other indicators is not stated. 
Hence a number of indicators were tested according to the following 
procedure :■— 
Aqueous solutions of arsenic trioxide and potassium hydroxide 
were prepared, their strength being represented by the following 
formulas: 
No. 1 , As(0H)3; No. 2, KOH; No. 3, 2K0H; No. 4, 3K0H; 
5 5 5 5 
respectively. Six test tubes of the same size were used for each 
series. Into these test tubes were placed the following solutions:— 
Tube No. 1 
5 mils of As(OH)3 
5 
+ 
5 mils of H 2 0 
Tube No. 2 
5 mils of As(OH)3 
+ 
5 mils of KOH 
5 
5 
Tube No. 3 
5 mils of As(OH)3 
+ 
5 mils of 2KOH 
5 
5 
Tube No. 4 
5 mils of As(OH)3 
+ 
5 mils of 3KOH 
5 
5 
Tube No. 5 
5 mils of KOH 
5 
+ 
5 mils of H s O 
Tube No. 6 
10 mils of H 2 0 
It will be noted that each solution as contained in the tubes was 
N/10 in strength, comparable in strength to the arsenical solutions. 
