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210. How much silicon should be obtained from 119 grammes of potassium silico-fluoride, and how much potassium would be needed for the decomposition ?

211. One hundred and twenty-three grammes of aluminium were heated in a current of silicon tetrachloride vapour. Give the weights of the products.

PENTADS.

NITROGEN.

212. How does nitrogen occur in nature ? Mention some gaseous and solid bodies which contain it.

213. When, by whom, and how was nitrogen discovered ?

214. Give a full account of any experiment which proves the existence of nitrogen in air.

215. Give two methods for the preparation of nitrogen from air.

216. Give four distinct methods for obtaining nitrogen gas from compounds of nitrogen. Give equations

217. What are the properties of nitrogen?

218. What volume of chlorine must be passed through ammonia so as to yield 10 litres of nitrogen gas at N.T.P.? 219. What volume of air contains

gramme of nitrogen?

I

220. How may nitrogen be directly combined with oxygen, tungsten, carbon, boron, and magnesium ?

221. How may the nitrogen contained in potassium nitrate be obtained in the free state?

222. What is the difference in weight between 10 litres nitrogen and 10 litres air, each gas being measured at N.T.P. ?

PHOSPHORUS.

223. What is the chief source of phosphorus and its compounds? What is the most abundant phosphate found in nature ? Name other naturally-occurring phosphates.

224. From what source do animals derive the phosphorus which is contained in their bones and blood ?

225. By whom and when was each modification of phosphorus discovered ?

226. Give the details of the process employed for the preparation of phosphorus from bone-ash. Represent all the reactions by equations.

227. In preparing phosphorus, sand is sometimes used along with charcoal for the final distillation. What is the advantage of this ? Calculate the quantity of phosphorus which should be obtained from a ton of calcium phosphate (a) using charcoal only, (6) using charcoal and sand.

228. The skeleton of a full-grown man weighs 24 pounds, and the bones contain 58 per cent of calcium phosphate. Calculate the weight of phosphorus in the skeleton.

229. Why are preparations of bone-ash frequently employed as manures ?

230. A piece of bone is heated (a) in a covered crucible, (6) in an open fire. Describe the substances obtained in each case, and state which would contain the larger proportion of phosphorus.

231. How is crude phosphorus purified ? How is it cast into sticks?

232. How is amorphous phosphorus obtained on the large scale ? How is it purified from traces of common phosphorus ?

233. How may amorphous phosphorus be converted into common phosphorus, and vice versâ ? How may these changes be shown on the small scale ?

234. Compare the properties of the two varieties of phosphorus, and point out the differences between them.

235. How could you prove, in spite of the great differences in properties, that common and red phosphorus are modifications of the same element ?

236. Two hundred and seven grammes of phosphorus pentoxide were obtained in each case by burning (a) phosphorus, () phosphine, in air. What weight of substance was used in each case ?

237. What is the weight at N.T.P. of 1,234 litres of phosphorus vapour ?

238. To what property of the element does phosphorus owe its name? Under what conditions does it lose this property ?

239. Describe a process for the detection of phosphorus in cases of poisoning.

240. A manufacturer prepares phosphorus from 169 tons of bones containing 537 per cent. of calcium phosphate. How much phosphorus should he obtain, and how much sulphuric acid and carbon should be required for the process ?

241. How has amorphous phosphorus been obtained in crystals, and what are the properties of this modification ?

242. How may phosphorus be directly combined with oxygen, chlorine, hydrogen, and sulphur ?

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