Chemistry . 
187 
XI. CHEMISTRY. 
13. Dr Wollaston's Test for Magnesia . — If a solution con- 
taining magnesia, decomposed by a mixture of phosphate and 
carbonate of ammonia, is spread upon a plate of glass, and if 
we trace any word, Magnesia for example, upon the glass thus 
covered, with the extremity of a glass rod, the word will appear 
in white characters. The magnesia re-dissolved by the excess of 
the carbonate, is precipitated upon the traces of the glass rod, in 
consequence of the expulsion of the carbonic acid by the heat 
disengaged by friction. When there is no precipitation on the 
traced characters, then no magnesia has been present in the so- 
lution. 
14. Method of making Green Fire . — When the following 
composition, which has been a desideratum in pyrotechny, is 
burned in a reflector, it sheds a beautiful green light over sur- 
rounding objects. It may likewise be employed in hre-works. 
Flowers of Sulphur, . . 13 parts. 
Nitrate of Barytes, . . 77 
Oxy muriate of potash, . , 5 
Metallic Arsenic, . . 2 
Charcoal, ... . 3 
The nitrate of barytes should be well dried and powdered, 
and then mixed with the other ingredients, all finely pulverised 
and triturated till they are perfectly mixed together. In order 
to make the combustion slower, a little calamine may be added. 
— Journal of Science , vol. xi v. p. 232. 
15. Fusion of Charcoal by Hare's Deflagrator. — - M r Hare 
had some time ago observed, that the charcoal points, when ig- 
nited by the instrument, “ assumed a pasty consistence, and ap- 
peared as if in a state of fusion.” This most important fact 
seems to have been placed beyond a doubt by Professor Silli- 
man, who has obtained some very curious and valuable results 
with the Deflagrator. 
When the charcoal points were brought into contact, and 
then withdrawn a little, the most intense ignition took place. 
The charcoal part of the positive pole shot out and increased 
