xxiv INTRODUCTION. 



It is almost impossible, merely by means of books, to teach the student 

 how to recognise minerals. Still, something may be effected in that way ; 

 and the following brief hints (chiefly compiled from Dana's Mineralogy) 

 may be of use, by enabling him, in the first instance, to ascertain to what 

 particular class a specimen may belong ; when a few essays with the blowpipe 

 will aid him in finding out the particular species. 



Thus — Carbonates may be distinguished as a class by means of Acids. 

 Muriatic acid, generally diluted with an equal quantity of water, is the acid 

 most frequently made use of for this purpose; but sulphuric or nitric acids, 

 diluted in a similar manner, afford the same results. Such a solution, dropped 

 on a carbonate (as, for instance, carbonate of lime) produces an effervescence 

 or disengagement of bubbles of carbonic acid, which gives place to the 

 stronger acid, for which the lime has greater afiinity. 



Sulphates, on the contrary, afford no effervescence with acids. When in 

 solution, they may be tested with a solution of a salt of baryta, when they 

 throw down a white precipitate of sulphate of baryta, which is insoluble 

 in water. None of the sulphates possess a metallic lustre, and they are often 

 colourless. 



Nitrates, when treated with strong sulphuric acid, give off white corrosive 

 vapours of nitric acid. 



Phosphates may generally be dissolved, without change, in muriatic and 

 nitric acids, and are decomposed by sulphuric acid. The phosphates which 

 are soluble produce a characteristic yellow precipitate on the addition of 

 nitrate of silver, as also do the neutral nitric solutions of the insoluble 

 phosphates. 



All the phosphates have an unmetallic lustre. IsTone of them are soluble 

 in water, or have any tnste, except one single phosphate of ammonia. The 

 pure phosphates also give off no odour before the blowpipe. 



Silicates, in many cases, gelatinize with acids, the silica forming a jelly 

 or separating in a gelatinous state. Sometimes this may be effected with 

 cold acid, but, generally, the mineral, previously reduced to a finely- 

 powdered state, is placed in strong acid, and then gently heated. After a 

 short time, as the solution cools, the jelly appears, or, in some cases, partial 

 evaporation is required before the jelly makes its appearance. 



Boi-ates, when reduced to powder, and heated with sulphuric acid, impart 

 a green colour to the flame, on the addition of alcohol. 



Sulphides have a metallic lustre, or an unmetallic lustre with a coloured 

 streak ; the only exceptions being Blende and Yoltzite, which have an 

 unmetallic lustre and an uncoloured streak. 



Chlorides all afford a white curdy precipitate with nitrate of silver, which 

 becomes dark or violet-coloured on exposure to the atmosphere. 



Fluorides, when pulverised and heated with strong sulphuric acid in a 

 platinum crucible, give off fumes of hydro-fluoric acid, which will corrode a 

 plate of glass placed over the crucible. 



Salts of Lime, \n solution (even in a diluted state), on the addition of 

 oxalic acid or oxalate of ammonia, afford a white precipitate of oxalate of 

 lime, which is insoluble in water, but is very soluble in any of the stronger 

 acids. 



