QUESTIONS AND PROBLEMS 127 



138. With what explosive mixture are lucifer matches tipped? How are 



safety matches prepared ? What is " amorphous phosphorus " ? 



139. Describe the preparation of phosphoric anhydride. Why must the 



materials and apparatus used be perfectly dry ? What happens 

 when it is mixed with water, and what further change takes place 

 on boiling the liquid ? 



140. Give an account of the experiments made which showed that there 



were three phosphates of calcium. Express their composition by 

 formulae, and state which of them is soluble in water. What is 

 meant by an "acid salt." How may the three salts be dis- 

 tinguished by name? 



141. Of what do bone ash, appatite, and coprolite consist? What is the 



action of sulphuric acid upon them, and of what does the 

 ** superphosphate of lime," thus obtained, consist ? Illustrate the 

 reaction by an equation. 



142. What is meant by " reverted phosphate," and under what conditions 



does reversion take place? For what reason is the ammonium 

 phosphate contained in Peruvian guano likely to be more easily 

 absorbed by crops, when applied as a manure, than super- 

 phosphate of lime ? 



143. What is the source of ** basic slag," and of what is it composed ? 



144. Give two methods for identifying phosphoric acid. 



^145. Find whether the phosphatic material contains soluble or insoluble 

 phosphate, or both. (Superphosphate of lime, bone meal, or 

 guano. ) 



Silica: Sand and Clay. 



146. What is silica, and how may silicon be obtained from it ? Express 



the reaction by an equation. 



147. What is soluble glass, and how may it be prepared ? Illustrate by 



an equation. 



148. Wliat is the action of sulphuric acid upon (i) a weak and (2) a 



strong solution of silicate of sodium ? Compare with the action 

 of sulphuric acid upon a weak and a strong solution of sulphite of 

 sodium. 



149. How may silica be obtained from a solution of silicic acid? What 



are the properties of silica in respect to colour and its solubility 

 in water, acids, and alkalies ? 



150. How does uncombined siHca occur in nature? What is the com- 



position of the minerals felspar, mica, china clay, asbestos, 

 meerschaum, and steatite ? 



