726 PROCEEDINGS OF SECTION J. 



Sulphuric acid is next taken, and similar work done under the 

 same five headings, which affords the opportunity for repetition of the 

 same chemical principles. He has studied the insoluble sulphates, 

 and at this stage is able to recognise a chloride and a sulphate, and the 

 metals which form an insoluble chloride or sulphate. 



Nitric acid is dealt with next on the same plan, nitrates being 

 formed by the general methods, and the same general principles ex- 

 plained. The production of nitric acid from nitrates is carried out, and 

 oxidation and reduction studied by experiments with ferrous sulphate, 

 potassium permanganate, and nitric acid. The complementary nature 

 of oxidation and reduction is brought out, and the wider meanings of 

 these, as signifying the increase or decrease in negative radical, whether 

 the simple oxygen radical or the negative radical of an acid. 



Hydrobromic and hydriodic acids are next dealt with. Bromine 

 and iodine are studied, and converted by aqueous sulphuretted hydrogen 

 into the halogen acids, from which, by neutralisation, the salts are 

 obtained. From these salts the elements are reproduced, differences 

 being observed, so that they may be each recognised. 



Carbonates, sulphites, and phosphates are next dealt with, studying 

 in the same way the most important reactions which may be grouped 

 under these headings. All through the work, which is very inade- 

 quately described here, the student is led to find out as much as possible 

 for himself. Chemical equations are eschewed, the chemical changes 

 involved being represented by less abstract methods. A great number 

 of chemical changes are metathetical, and easily represented without 

 the use of symbols. For example, the precipitation of silver chloride 

 is represented thus — 



Silver \/ nitrate ^ Sodium nitrate 

 Sodium /\ chloride ~^ Silver chloride 



X 



Also the production of copper chloride from copper oxide, thus — 



Copper \y oxide j. Copper chloride 



Hydrogen /\ chloride ~^ Hydrogen oxide 



The last exercise is on the sulphides, salts -of hydrosulphuric acid, 

 excluding metals, which he has learnt to form in soluble chlorides. 

 All other metallic salts are first examined, and divided into two classes, 

 according as their sulphides are soluble or insoluble in water. Some 

 he finds to be insoluble in hydrogen chloride, others soluble in hydrogen 

 chloride, but insoluble in ammoniacal solution. These are further 

 tested for solubility in other solvents, and a scheme of classification 

 drawn up. He has already learnt how to recognise chlorides, bromides, 

 phosphates, &c., and he is now conversant with the principles of quali- 

 tative analysis. 



As a rather more complicated instance of the method of representing 

 the trend of chemical reactions, we may consider the oxidation of a 



