W. Gibbs—Contributions to Chemistry. 215 
ical purposes, since it fails entirely when salts of ammonium or 
of the alkaline metals are present. The oxalates are also in 
such a state of subdivision that it is almost impossible to ignite 
them without loss. The oxyds of copper, cadmium, zinc, man 
hese and magnesium, are also completely precipitated from their 
sulphates by oxalic acid and alcohol, but not in presence of alka- 
line salts, The same is true of both mercurous and mercuric 
nitrates. In the few cases in which this mode of precipitation will 
find application in practice it will probably be best to determine 
the oxalic acid in the oxalate by hypermanganate of potash. 
In a former paper I have stated that the sulphids of cobalt 
and nickel thrown down from boiling solutions by a boiling so- 
lution of sulphid of sodium may be washed without oxydation 
Upon the filter. The difficulty of preparing pure sulphid of 
sodium has, however, been an objection to this method.* This 
difficult may easily be removed by dissolving the crystallized 
tetrahedral sulphid, Na,S+9aq, in alcohol of 90 per cent, fil- 
ming and allowing the solution to crystallize. After two or 
three crystallizations the pure sulphid may be dried over sulphu- 
Mic acid in vacuo and the white effloresced mass preserved in a 
well stoppered bottle. The sulphid is chemically pure. 
§4. On the employment of sand and glass filters in quantitative 
analysis. 
Sufficient attention has not been paid to the advantages of 
ters of sand. and glass over those of paper, when precipitates 
carried out this suggestion with : hor- 
Sughness, obtained the following results in three analyses of tar- 
tar-emetic, 
[00917 -oniett 0:0463 gr. Sb,S, — 36°09 per cent Sb. 
IL ogasesy es osog. «= 8808 
UL 01766 gr, « 90891 gr “ = 36-07 
The formula requires 35°92 per cent (Sb=120). LT pees 
Th the first a second analyses the rer grea sulphid eon 
dtied at 875°C, In the third the funnel had the shape of a tul 
i, p wis Journal, vol xxxvii, p. 350, also Zeitschrift fir Analytische Chemie, Bd. 
‘“c “ 
