Determination of Arsenic and Antimony Together: Instead of separating arsenic from antimony in the hydrochloric-tartaric acid solution which was finally obtained, dilute the solution to four times its volume; pass sulphuretted hydrogen to saturation; filter the combined sulphides on a 4 cm. filter (weighed and dried in weigh-bottle at 110° C.); wash with water, absolute alcohol, carbon bisulphide, and finally absolute alcohol again, very carefully; then dry at 110° C., cool and weigh. More about Electrolytic Assay.
By allowing to dried filters in weigh-bottles the same time for cooling in the desiccator when getting weight of bottle and filter-paper only, as afterwards when filtered sulphides are dry and ready for weighing, very uniform results are obtained.
Arsenic being precipitated as As2S3 and antimony as Sb2S5, their respective factors being 0.609 and 0.600, the factor 0.6 is used in calculating, from the weight of the combined sulphides, the percentage of arsenic plus antimony.
Determination of Arsenic as Trisulphide
Re-dissolve the sulphides in a solution containing hydrochloric acid, water and chlorate of potash. Dilute to at least twice the volume. Pass through the warm solution sulphuretted hydrogen to saturation, to insure the thorough reduction of the solution. Arsenic will be precipitated as trisulphide. After 5 ….Read more