ON TEACHING CHEMISTRY. 305 
and dropped into the bottle a, from which the tube B has been removed ; 
a little water is then added (about 5 cubic centims.) and the chalk is 
shaken out of the paper; about 5 cubic centims. of nitric acid is now 
poured into the tube B, which is then carefully replaced in the bottle a. 
Fi4. 1. 
5 
Cem 
(= g 
/ 
“if 
aad 
— 
The cork having been inserted, connection is established by means of the 
flexible tube c with the bottle p. The side tube having been so adjusted 
that the end ¢ is on a level with the water in the bottle p, the measuring 
cylinder H is so placed that any water which runs from e may be col- 
lected in it, and the bottle a is then carefully tilted so that the acid may 
gradually run out of the tube B into A; gas is at once given off and 
expels water from p. As the water sinks in D the side tube £ is lowered so 
that its orifice remains about on a level with the water inp. The water 
is then measured. Several experiments should be made and the results 
should be compared by calculating the volume of gas which would have 
been obtained, supposing, say, 100 grams of the chalk had been dissolved. 
5. In this way it is ascertained that chalk-stuff is characterised by 
@) yielding between 56 and 57 percent. of lime, which increases by about 
3 per cent. when slaked; and (2) by yielding about 22,000 cubic 
centims. of chalk-gas per 100 grams when dissolved in acid. 
6. Comparing lime with chalk, it is found that if the chalk be 
thoroughly burnt no gas is evolved on dissolving the recently slaked 
lime in acid; this result serves at least to suggest that the gas which 
18 given off when chalk is dissolved in acid is perhaps expelled during 
the conversion of chalk into lime. The loss in weight which occurs is 
therefore determined, and when it is ascertained that it is very nearly 
the sg as when chalk is burnt, no room is left for doubt that the same 
; x 
