ON TEACHING CHEMISTRY. , 301 
outline maps be coloured, so as to indicate the different rainfall of 
different districts. 
2. Call attention to the geographical distribution of water, &. ; also 
to the work which it does in nature (cf. ‘Geikie’s Physical Geography,’ 
‘Huxley’s Physiography,’ c&c.), illustrating this part of the subject, 
especially at an inland school, by lantern photographic slides of ships, 
sea-coasts, Niagara Falls, &c. &e. 
3. Call attention to the disappearance of water, i.e. the drying up of 
rain, the drying of clothes, &c., and lead the pupils to notice that this 
takes place most quickly in hot weather and in warm places; then let 
them pour water into a clock glass placed either over a saucepan in 
which water is boiled by a gas-burner (or petroleum or spirit lamp, if 
gas be not available), or in a small gas cooking-stove ; they will see that 
the water evaporates, leaving a certain amount of residue. [At this stage 
experiment on the extent to which water evaporates out of doors and 
indoors under different conditions and at different times of the year by 
exposing water in weighed glass (crystallising) dishes about 4 inches in 
diameter, and weighing at intervals. Also call attention to the fact 
that in certain states of the weather things become damp, and that 
moisture is sometimes deposited on the windows in cold weather; then 
let the condensation be noted of a liquid indistinguisbable from water, 
which occurs, for instance, when a closed flask filled with water and ice 
is exposed in a room. Let some seaweed enclosed in a muslin bag be 
hung up out of doors where it cannot be wetted by rain, and have it 
weighed daily. At the same time have the temperature, direction of the 
wind, and character of the weather noted. Later on have the dry and 
wet bulb thermometer read daily. Have the changes in weight of the 
seaweed and the dry and wet bulb thermometer readings represented by 
curves. lead the pupils to contrast and discuss the results.] The ex- 
periment should then be repeated with a known quantity of water and a 
weighed glass dish, so as to determine the amount of residue; the 
character of the residue should he noticed. Discuss the origin of the. 
water, and point out whence the residual matter may have come. Next, 
if a well water was taken, let a local river or pond water be examined in 
a similar way, then rain water, and, if possible, sea water. 
4, Let an ordinary 2-oz. narrow-mouth stoppered bottle, having 
a nick filed down the stopper, be filled with each of the waters and 
weighed, and let the operation be repeated several times with each water, 
so that the eaperimental error may be ascertained ; it will be found that 
the different waters, sea-water excepted, have practically the same 
density. At this stage arithmetical exercises relating to the weight of 
known bulks, and vice versd, of water, the quantities of dissolved solids 
present in given bulks of various waters, &ce. &c. may advantageously 
be set; these should be solved practically by actual measurement in as 
many cases as possible. 
5. Next ask, ‘But what becomes of the water when driven off by 
heat ?’ If ithave not been noticed that water collects (condenses) on some 
object near at hand, let a cold object be held over boiling water, then let 
water be boiled in a glass flask connected with a glass condenser. 
Afterwards have water distilled in larger quantity from a tin (2-gallon) 
can. The density of the distilled water should then be determined and 
its behaviour on evaporation. Data would thus be accumulated render- 
ing it possible to explain the drying up of water under ordinary con- 
