172 CHEMISTRY. 



disinfectant? 221. Describe a case of combustion in chlorine. Why does 

 a candle smoke so badly in chlorine ? How does oil of turpentine act in 

 chlorine gas? 222. What is hydrochloric acid, and what are its properties? 

 What is its commercial name ? 223. Show how this acid can be obtained 

 synthetically. 224. Describe the common mode of preparing hydrochloric 

 acid. What will be formed if you add manganese dioxide to the materials 

 employed ? 225. What is aqua regia ? Whence comes its name ? 22G. 

 What is said of the oxygen compounds of chlorine ? What bodies form 

 when chlorine gas is passed into a solution of potassium hydrate ? 228. 

 What is said of iodine ? 229. What of its properties ? 230. How does it 

 support combustion? 231. What is noticeable about bromine ? 232. Of 

 what use is fluorine itself? Explain a method of etching glass. 



CHAPTER XII. 



SULPHUR. 



233. Occurrence of Sulphur. Sulphur is a very abundant 

 substance in nature. In the combinations of sulphur with 

 copper, lead, silver, and many other metals, forming sul- 

 phides, we have their most important ores. Much of the sul- 

 phur which is used is obtained from a sulphide of iron, or 

 iron pyrites. Large beds of native sulphur are often found, 

 especially in volcanic localities. Combined with oxygen as 

 sulphuric acid, it exists in great amount in the sulphates, the 

 most abundant of which is the sulphate of lime, called gyp- 

 sum or plaster of Paris. It enters also in small proportion 

 into the composition of both vegetable and animal substan- 

 ces, being in considerable quantity in some of them, as in 

 beans, pease, horseradish, onions, etc., in the vegetable world, 

 and in eggs, hair, horns, hoofs, etc., in the animal. 



234. Forms of Sulphur. Sulphur is disposed to take a 

 crystalline arrangement, and always does to a greater or 

 less degree. Even when cast in roll there is some crystal- 

 lization, imperfect and irregular, so that when it is held in 



