30 Improvements in Physical Science [Jans 
numbers two, three, four. (See Annals of Philosophy; vol. v. p. 
237.) 
Gaultier de Claubry and Stromeyer have ascertained that starch 
is the most delicate re-agent for detecting the presence of iodine. 
The iodine must be uncombined. Starch does not detect iodine in 
a solution containing hydriodic acid or iodic acid. But if an acid 
be poured in so as to disengage the iodine, the starch shows the 
presence of that substance by the indigo-blue colour which it 
assumes. (Gilbert’s Annalen, vol. xlix. p. 146; and Ann. de 
Chim. vol. xciii. p. 85.) 
M. Gaultier de Claubry has analyzed sea water and several fuci 
from the English channe]. He could detect no iodine in sea water ; 
but he feund it in the following sea plants : fucus saccharinus, fucus 
digitatus, fucus vesiculosus, fucus siliquosus, fucus filam. (See 
Ann. de Chim. vol. xe. p. 75, 113.) 
I have been informed that Mr. Smithson Tennant before his death 
succeeded in detecting iodine in sea water; but I know nothing 
respecting the method which he followed in his investigation. 
Sir Humphry Davy has discovered a solid combination of iodine 
and oxygen. I place it here because the discoverer does not con- 
sider it as acid unless it be combined with water, though I entertain 
a different opinion from this ingenious chemist. It is obtained by 
exposing iodine to the action of euchlorine gas. The gas is ab- 
sorbed, and a solid substance formed consisting of two compounds ; 
the first, a combination of chlorine and iodine; the second, of 
oxygen and iodine. By the application of a gentle heat, the first 
compound is driven off, and the second remains. Sir H. Davy 
gives it the name of oxiodine ; but perhaps the term oxiodic acid 
would be more proper. It is white, and semi-transparent ; has no 
smell; but a strong astringent sour taste. It sinks rapidly in sul- 
phuric acid. A heat rather below 600° decomposes it. According 
to Davy’s experiments, it is composed of 
MOE S B85, 5 ereco! it siieys tq BAe ire aa shanteles 
OSV SERS, 4:52 G6 we cgy LBS), Sseroanny oll 
100°00 
This compound is deliquescent. It is very soluble in water. The 
solution reddens vegetable blues, and then destroys them. It acts 
upon all the metals, and combines with alkalies, earths, and metallic 
oxides. It unites likewise with the acids, and forms with them solid 
compounds, which possess remarkable properties. 
IV. SIMPLE COMBUSTIBLES. 
1. Hydrogen.—One of the most important experiments which 
can well be made in the present state of the science of chemistry is 
related in the Annals of Philosophy, (vol. vi, p. 234) on the autho- 
rity of Van Mons. Dobereiner introduced a globule of mercury 
into a vessel of water, and placed it near the negative wire of a 
galvanic battery. Oxygen gas was given out irom the positive wire; 
but no gas whatever was extricated from the negative wire, The 
