IOWA ACADEMY OP SCIENCE 
143 
THE ANALYSIS OP SMALTITE WITH SPECIAL REPERENCE TO THE 
ESTIMATION OP ARSENIC AND COBALT. 
BY NICHOLAS KNIGHT. 
A gram of the substance is weighed into a porcelain crucible of 150 c. c. 
capacity, 50 c. c. of dilute nitric acid are added, and evaporated to dryness on 
the water hath. The nitric acid is removed with sulphuric acid. This treat- 
ment changes the lead sulphide that may be present to lead sulphate, which 
with the silica is removed by filtration. 
The filtrate is diluted to a volume of 200 c. c. and heated to 60°-70°, while a 
stream of hydrogen sulphide is run into the liquid for three to six hours. This 
precipitates arsenic, bismuth and copper, all the other substances remaining 
in solution. After filtering and washing the precipitate in cold water, it is 
treated with warm potassium sulphide. This dissolves arsenic sulphides, while 
bismuth and copper sulphides remain unchanged. 
The solution of arsenic is evaporated to dryness on the water hath, and if 
sulphides of arsenic and copper separate from the solution as may happen, 
these are filtered, and added to the other portion. 
The arsenical residue is transferred to a 150 c. c. crucible and five to seven 
grams of solid caustic potash are added. Then a stream of chlorine is run 
into the crucible for twenty or thirty minutes, or until the contents of the 
crucible bleach litmus paper. 
With the crucible covered by a watch glass about 50 c. c. of dilute hydro- 
chloric acid are added, and then evaporated until crystals appear. The opera- 
tion is then repeated, using 50 c. c. of concentrated hydrochloric acid. 
By the use of hot water, the contents of the crucible are transferred to a 
beaker glass and filtered to- remove the sulphur and silica. The filtrate con- 
taining the arsenic is diluted quite largely with water and kept at a tempera- 
ture of 60°-70°, while a stream of hydrogen sulphide is introduced for three 
to six hours. The arsenic sulphide may he collected in a Gooch crucible or on 
a tared filter. 
The reactions: 
CoAs, -t- 6HNO3 = Co(N03)2 2H3ASO, -1- 4NO. 
2H3ASO4 5HoS = AS0S5 8H0O. 
AS2S5 -1- 3KoS = 2K3ASS4. 
K 3 ASS 4 + 40KOH 32C1 = 4 K 2 SO, -f 32KC1 -f 2 OH 2 O -F K 3 ASO 4 . 
Pot arsenate. 
The excess of KOH and Cl becomes 2KOH - 1 - 2C1 = KCIO 4- KCl -f H 2 O and 
3KC10 = KCIO 3 -f 2KC1. 
Adding dilute HCl, 
2HC1 -t- KCIO = KCl -f 2C1 -f HoO, the hypochlorite and also the K 2 CO 3 are 
decomposed. The K 2 CO 3 is formed by the action of the CO 2 of the atmosphere 
upon the caustic potash. 
It is also necessary to add Cone., HCl to decompose the KCIO3 as follows: 
