S24 NEW ZEALAND NATURE-STUDY BOOK 
Norte :—Some little time should here be devoted to revising the 
lessons already given on the Earthworm in order to bring home 
the important part which this animal plays in the production of 
humus and the formation of soil. 
The general characters of the soils in the neighbourhood might 
be determined e.g. whether light or heavy—whether sandy soils 
or clay soils, or loams. 
The examination of gravel pits, shingle beds, and quarries, will 
often determine whether the soil be local or transported. 
The formation of a salt by the union of an acid and a base is: 
capable of simple demonstration. Take a bottle of soda-water 
and, after uncorking, allowing the effervescence to subside, and 
diluting the liquid, pour some of it into a vessel containing lime 
water. The whole at once becomes milky owing to the presence 
of the insoluble carbonate—that is, the acid carbonic acid has 
united with the base lime to form the salt carbonate of lime. 
The soda-water must not contain too much carbon-dioxide as 
carbonate of lime is soluble in water holding an excess of this gas 
in solution. 
In each case the solutions are colourless—so that the sudden 
appearance of the precipitate will illustrate the change which has 
taken place. 
Salts may also be formed by the action of an acid on a metal. 
Place a few pieces of granulated zine in a beaker and add a small 
quantity of dilute hydrochloric acid. Bubbles of hydrogen gas 
will be given off and the zine will gradually disappear. Filter the 
solution and observe the clear colourless filtrate. Pour this into 
a porcelain crucible and evaporate over a bunsen or spirit-lamp 
flame. Notice the deposit left at the bottom and on the sides of 
the crucible—a substance differing entirely from the original zine. 
The hydrochloric acid has combined with the metal to form the 
salt, zinc chloride. If sulphuric acid be used, the salt formed 
will be zine sulphate. 
The reactions between certain acids and salts may be used for 
purposes of further illustration. Dissolve a few crystals of barium 
chloride in some water, and into a very weak solution of this pour 
a few drops of dilute sulphuric acid—a dense white precipitate will 
at once appear. The sulphuric acid has united with the barium 
to form the insoluble salt, barium sulphate. 
The reactions which result in the formation of an insoluble salt, 
and which therefore can be seen taking place by a class, are 
perhaps the best for purposes of illustration. 
