cipitate of a brilliant red colour (the iodide of mercury) is instantly produced: this can be collected by pouring the mixture on filtering paper, the iodide of mercury remaining behind: the pupil is recommended to acquire the habit of thus separating precipitates.

50.-In concluding the article on iodine, it is advisable to state, that when it combines with a substance below it, the gas chlorine, for example, the compound is termed the chloride of iodine; but when with bodies above it, such as potassium, or mercury, we style the compound the iodide of potassium, or mercury.

QUESTIONS.

179. When was iodine discovered?

180. What is the difference in colour between iodine when solid and in the state of vapour?

181. What is the derivation of the term?

182. Does it affect the skin?

183. In what proportion is it soluble in water?

184. What is tincture of iodine?

185. Describe the experiment by which the vapour of

iodine was exhibited..

186. Explain how starch is detected by iodine.

187. What do we understand by the term iodide ?

188. When iodine is mixed with chlorine, why do we say chloride of iodine, and not iodide of chlorine ?

SULPHUR.

52. This useful and extraordinary agent seems to be universally scattered over the globe-sometimes in its simple or elementary state, as in volcanic countries, but generally in combination with other bodies. It is a solid of a pale, yellow colour, nearly insoluble in water, exceedingly brittle, and possessing but little taste or smell. It melts at the temperature of 226 Fahrenheit's thermometer. By increasing the heat it passes off in the state of vapour, which, meeting with a cold surface, is condensed into a fine yellow powder, termed sublimed sulphur, or flowers of sulphur.

Experiment 47.-Heat a spoonful of sulphur in a crucible; arrest the vapour by holding over it an inverted cup, kept cool. This illustrates, in a pleasing way, the process by which sulphur is obtained from the sulphurous grounds in Italy, and from the ores of the metals, copper, lead, and iron, in Great Britain and other countries. This process is termed by miners roasting; when thus united, either naturally or arti ficially, with the metals, the compounds are termed sulphurets. It may not be uninteresting to state here, that the county of Wicklow, in Ireland, is vieing with Sicily in the manufacture of sulphur.

Experiment 48.-To prove that such is the composition of a sulphuret, we have but to apply a piece of roll sulphur, termed popularly cane brimstone, to the

on a fire to extinguish it when danger is apprehended by soot being ignited in the chimney. Sulphur possesses the singular property of checking fermentation in wine vats, without injuring the wine. It is an excellent medium for taking impressions from seals. (Vide exper. 48.) Its principal uses are, for the manufacture of vermillion or cinnabar, gunpowder, sulphuric acid, or vitriol, and some important medicines.

Experiment 48.-Melt some sulphur in a clean ladle; keep it for some minutes in that state, and pour it on medals surrounded with circles of card; the impressions generally are beautiful.

Experiment 49.-To illustrate its bleaching property, suspend a red rose over the fumes of burning sulphur (sulphurous acid); in a few minutes it will be white.

QUESTIONS.

194. Is sulphur an abundant element?

195. Is it ever found pure?

196. Is it soluble in water?

197. What is understood by the term sublimed sulphur, or flowers of sulphur?

198. What is a sulphuret?

199. If you apply a piece of solid sulphur to red-hot iron, what is formed?

200. Describe the process by which they obtain sulphur in Sicily?

201. Do you remember how many tons of sulphur Great Britain consumed in 1839 ?