CAPTAIN NOBLE AND MR. F. A. ABEL ON FIRED GUNPOWDER. 
69 
datioii of any of the constituents. After drying and washing the residue, it was intro- 
duced, with its filter, into a small flask ; a little potassium bichromate was added before 
addition of nitric acid, to guard against violent reaction and the possibility of minute 
quantities of sulphur escaping as sulphuretted hydrogen. The oxidation was completed 
by the addition of potassium chlorate ; the liquid, after sufficient dilution, was filtered 
and evaporated, the residue redissolved in water, with addition of chlorhydric acid, and 
the sulphuric acid determined in the solution by the usual method. 
The proportion of charcoal contained in the insoluble residue was, in most instances, 
so small that no importance could be attached to any attempt to determine the quantity. 
In a few cases its amount was determined by combustion. 
e. Potassium monosulphide.-— The method pursued differed but very slightly from 
that adopted by Bunsen and Sciiischkoff. The aqueous solution, separated from the 
insoluble portion, was digested with pure ignited cupric oxide in a well-closed flask, 
with occasional agitation, until it became colourless. The oxide containing sulphide 
was then filtered off, thoroughly washed, and the sulphur was determined in it by oxi- 
dation according to the method just described (d). 
f. Potassium sulphate. — The filtrate obtained after the treatment with cupric oxide 
just described (or a measured quantity of it, if the entire residue was operated upon at 
one time) was mixed with chlorhydric acid and boiled to expel the sulphurous acid 
resulting from the decomposition of hyposulphite ; the liquid was then separated by 
filtration from liberated sulphur, and the sulphuric acid determined as barium sulphate. 
g. Potassium hyposulphite. — The solution obtained by treatment, as above described, 
of about 4 grammes of the residue (or a sufficient volume prepared from the entire 
residue) was acidulated with acetic acid; 8 or 4 cub. centims. of starch solution were 
added, and the hyposulphurous acid determined by means of a standard iodine solution. 
h. Potassium sulphocyanate. — A solution of the residue, after separation of the 
insoluble portion and the soluble sulphide, was carefully acidified with a measured 
quantity of dilute chlorhydric acid, so as to avoid separation of sulphur. The oxida- 
tion of the hyposulphite was then effected by the gradual addition of a very dilute 
solution of ferric chloride until the liquid exhibited a permanent pink tint. A mea- 
sured quantity of the ferric solution was afterwards gradually added until the greatest 
attainable depth of colour was produced. To determine what was the amount of 
sulphocyanate thus arrived at, a volume of water corresponding to that of the original 
solution tested was mixed with equal volumes of the dilute chlorhydric acid and ferric 
chloride to those used in the previous experiments. A solution of potassium sulpho- 
cyanate of known strength was then gradually added until a depth of colour cor- 
responding to that of the actual assay was produced. 
i. Potassium carbonate. — After the usual treatment of a solution of the residue with 
cupric oxide, pure manganous sulphate or chloride was added to the liquid in excess; 
the resulting precipitate might generally be washed by decantation in the first instance ; 
after complete washing it was transferred to a small flask suitably fitted for the libera- 
