TESTING FOR ANTIMONY AND ARSENIC. 459 
spheric air, a similar effect is produced; but the time required 
for the complete change is too long for the operation in the 
cold to be made available in preference to that in which heat 
is applied. In an experiment made in the cold, not more than 
half of the antimony was dissolved in thirty hours. 
My attention was next turned to experimenting upon copper 
coated with arsenic. I exposed some alternately to the action 
of boiling dilute solution of potash and to air in a tube ; and, 
as might be expected, the arsenic became oxidized, and dis- 
solved in the solution. It, however, was not converted merely 
into arsenious acid, but into arsenic acid; for, after filtering 
the alkaline liquor, I slightly acidulated a portion of it with 
diluted nitric acid, and then added caustic ammonia till rather 
in excess; after which I evaporated to dryness, dissolved the 
dry residue in a few drops of water, and tested with nitrate of 
silver, which gave the brick red precipitate, indicative of 
arsenic acid. I acidulated the other portion of the alkaline 
liquor with hydrochloric acid, and then passed sulphuretted 
hydrogen gas, which did not immediately cause any yellow 
precipitate, but in a few hours I observed that a light yellow 
precipitate was slowly forming, and in twenty-four hours a 
considerable quantity of a bright lemon-yellow precipitate 
had fallen and covered the bottom of a half-ounce phial, in 
which I had corked the liquor up to keep in the sulphuretted 
hydrogen and exclude atmospheric air. The slow formation 
of the yellow precipitate confirmed the nitrate of silver test 
in showing the metal to have been converted into arsenic 
acid. 
This fact, of the conversion into arsenic acid, can be taken 
advantage of in separating antimony from arsenic when both 
have been deposited on copper by Reinsch’s process. What 
is required is to oxidize and dissolve the mixed deposit by the 
alternate action of boiling dilute solution of potash and ex- 
posure to the air in the tube, then to filter the solution, 
acidulate it, and pass sulphuretted hydrogen gas through it; 
and as soon as the orange precipitate of antimony has begun 
to collect itself together and settle, to take out this antimonial 
precipitate by filtering, setting aside the clear filtered liquor 
in a corked phial, whereby, in some hours, the bright yellow 
sulphuret of arsenic falls. 
When the deposit of antimony or arsenic is so thick as to 
readily crack off and not adhere to the copper, I think it is 
preferable to pursue the method in which the two heating 
operations are required ; or else to adopt Dr. Odling’s per- 
manganate process ; for if the deposit falls off the copper in 
scales or films when in the alkaline liquor, I do not find it 
