Chemistry and Chemical Arts. 147 
the chlorine gas to react upon liquid ammonia, and measuring the 
volume of nitrogen which results from the reaction; 6. Calcination 
with sal-ammoniac and measuring the gas evolved; 7. Ebullition 
with oxalic acid and estimating the carbonic acid produced. ‘The 
5th method is pronounced the best. The 4th is also good, but the 
6th and 7th are erroneous.—Idem. 
27. New method of preparing Zaffre in Sweden. (Dict. Techno. 
t. 19, p. 14.)—The oar is roasted until the greater part of its arse- 
nic is expelled, after which a sufficient quantity of concentrated sul- 
phuric acid is mixed with it to form a thick paste, which is exposed 
to a moderate heat, at first, and afterwards pushed to a cherry red, 
for one hour. The sulphate thus obtained, is reduced to a powder 
and dissolved in water; and to it a solution of carbonate of potash is 
gradually added, in order to separate the iron, and when it is perceiv- 
ed by the blue color that the cobalt is thrown down, the supernatant 
liquid is decanted and filtered, and the cobalt is precipitated by means 
of a solution of a silicated potash, which is prepared by heating in 
an earthen crucible a mixture of 10 per cent of potassa, 15 of well 
pulverized quartz, and one of charcoal, and treating the melted mass 
with boiling water. ‘The silicate of cobalt thus prepared, is supe- 
rior to that obtained in any other way for staining porcelain, or for 
the manufacture of blue glass—Idem. 
28. Gas Lights.—We abstract the following from the reports of 
M. Povituer upon the results obtained by M M. Boscavy and 
Dawre in the manufacture of illuminating gas from rosin. The first 
object was to determine by numerous experiments the illuminating 
power of gas from rosin, whether burnt through orifices of a circular 
shape (like the carcel or argand lamp) or from flat openings which 
give a fan-shaped flame of different dimensions. In all the experi- 
ments the flame of a carcel lamp was taken for unity. This lamp 
and the orifice submitted to experiment, was made to shine upon a 
sheet of white paper, drawn upon a frame, while a cylindrical stem 
between it and the lights, projected upon the paper their shadows. 
The orifice being fixed, the lamp was removed or brought nearer, until 
the shadows perfectly corresponded. In the round orifice the illumi- 
nating power of the gas from rosin was more than double that from oil- 
gas; in the flat orifices, it was only one and three quarters greater. 
